Merge pull request #91 from SELab-2/feat/service-layer

feat: Service & controller layer
2025-03-13 21:58:02 +01:00 · 2025-03-13 21:58:02 +01:00 · 4234a2e6e9
commit 4234a2e6e9
parent edd643710d 942df9634f
79 changed files with 2740 additions and 534 deletions
--- a/backend/config.js
+++ b/backend/config.js
@ -0,0 +1,7 @@
+// Can be placed in dotenv but found it redundant
+// Import dotenv from "dotenv";
+// Load .env file
+// Dotenv.config();
+export const DWENGO_API_BASE = 'https://dwengo.org/backend/api';
+export const FALLBACK_LANG = 'nl';
+export const FALLBACK_SEQ_NUM = 1;
--- a/backend/src/config.ts
+++ b/backend/src/config.ts
@ -1,4 +1,5 @@
 import { EnvVars, getEnvVar } from './util/envvars.js';
+import { Language } from './entities/content/language.js';

 // API
 export const DWENGO_API_BASE = getEnvVar(EnvVars.LearningContentRepoApiBaseUrl);
@ -7,3 +8,5 @@ export const FALLBACK_LANG = getEnvVar(EnvVars.FallbackLanguage);
 // Logging
 export const LOG_LEVEL: string = 'development' === process.env.NODE_ENV ? 'debug' : 'info';
 export const LOKI_HOST: string = process.env.LOKI_HOST || 'http://localhost:3102';
+
+export const FALLBACK_SEQ_NUM = 1;
--- a/backend/src/controllers/assignments.ts
+++ b/backend/src/controllers/assignments.ts
@ -0,0 +1,76 @@
+import { Request, Response } from 'express';
+import { createAssignment, getAllAssignments, getAssignment, getAssignmentsSubmissions } from '../services/assignments.js';
+import { AssignmentDTO } from '../interfaces/assignment.js';
+
+// Typescript is annoy with with parameter forwarding from class.ts
+interface AssignmentParams {
+    classid: string;
+    id: string;
+}
+
+export async function getAllAssignmentsHandler(req: Request<AssignmentParams>, res: Response): Promise<void> {
+    const classid = req.params.classid;
+    const full = req.query.full === 'true';
+
+    const assignments = await getAllAssignments(classid, full);
+
+    res.json({
+        assignments: assignments,
+    });
+}
+
+export async function createAssignmentHandler(req: Request<AssignmentParams>, res: Response): Promise<void> {
+    const classid = req.params.classid;
+    const assignmentData = req.body as AssignmentDTO;
+
+    if (!assignmentData.description || !assignmentData.language || !assignmentData.learningPath || !assignmentData.title) {
+        res.status(400).json({
+            error: 'Missing one or more required fields: title, description, learningPath, language',
+        });
+        return;
+    }
+
+    const assignment = await createAssignment(classid, assignmentData);
+
+    if (!assignment) {
+        res.status(500).json({ error: 'Could not create assignment ' });
+        return;
+    }
+
+    res.status(201).json({ assignment: assignment });
+}
+
+export async function getAssignmentHandler(req: Request<AssignmentParams>, res: Response): Promise<void> {
+    const id = +req.params.id;
+    const classid = req.params.classid;
+
+    if (isNaN(id)) {
+        res.status(400).json({ error: 'Assignment id must be a number' });
+        return;
+    }
+
+    const assignment = await getAssignment(classid, id);
+
+    if (!assignment) {
+        res.status(404).json({ error: 'Assignment not found' });
+        return;
+    }
+
+    res.json(assignment);
+}
+
+export async function getAssignmentsSubmissionsHandler(req: Request<AssignmentParams>, res: Response): Promise<void> {
+    const classid = req.params.classid;
+    const assignmentNumber = +req.params.id;
+
+    if (isNaN(assignmentNumber)) {
+        res.status(400).json({ error: 'Assignment id must be a number' });
+        return;
+    }
+
+    const submissions = await getAssignmentsSubmissions(classid, assignmentNumber);
+
+    res.json({
+        submissions: submissions,
+    });
+}
--- a/backend/src/controllers/classes.ts
+++ b/backend/src/controllers/classes.ts
@ -0,0 +1,77 @@
+import { Request, Response } from 'express';
+import { createClass, getAllClasses, getClass, getClassStudents, getClassStudentsIds, getClassTeacherInvitations } from '../services/class.js';
+import { ClassDTO } from '../interfaces/class.js';
+
+export async function getAllClassesHandler(req: Request, res: Response): Promise<void> {
+    const full = req.query.full === 'true';
+    const classes = await getAllClasses(full);
+
+    res.json({
+        classes: classes,
+    });
+}
+
+export async function createClassHandler(req: Request, res: Response): Promise<void> {
+    const classData = req.body as ClassDTO;
+
+    if (!classData.displayName) {
+        res.status(400).json({
+            error: 'Missing one or more required fields: displayName',
+        });
+        return;
+    }
+
+    const cls = await createClass(classData);
+
+    if (!cls) {
+        res.status(500).json({ error: 'Something went wrong while creating class' });
+        return;
+    }
+
+    res.status(201).json({ class: cls });
+}
+
+export async function getClassHandler(req: Request, res: Response): Promise<void> {
+    try {
+        const classId = req.params.id;
+        const cls = await getClass(classId);
+
+        if (!cls) {
+            res.status(404).json({ error: 'Class not found' });
+            return;
+        }
+        cls.endpoints = {
+            self: `${req.baseUrl}/${req.params.id}`,
+            invitations: `${req.baseUrl}/${req.params.id}/invitations`,
+            assignments: `${req.baseUrl}/${req.params.id}/assignments`,
+            students: `${req.baseUrl}/${req.params.id}/students`,
+        };
+
+        res.json(cls);
+    } catch (error) {
+        console.error('Error fetching learning objects:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+export async function getClassStudentsHandler(req: Request, res: Response): Promise<void> {
+    const classId = req.params.id;
+    const full = req.query.full === 'true';
+
+    const students = full ? await getClassStudents(classId) : await getClassStudentsIds(classId);
+
+    res.json({
+        students: students,
+    });
+}
+
+export async function getTeacherInvitationsHandler(req: Request, res: Response): Promise<void> {
+    const classId = req.params.id;
+    const full = req.query.full === 'true'; // TODO: not implemented yet
+
+    const invitations = await getClassTeacherInvitations(classId, full);
+
+    res.json({
+        invitations: invitations,
+    });
+}
--- a/backend/src/controllers/groups.ts
+++ b/backend/src/controllers/groups.ts
@ -0,0 +1,95 @@
+import { Request, Response } from 'express';
+import { createGroup, getAllGroups, getGroup, getGroupSubmissions } from '../services/groups.js';
+import { GroupDTO } from '../interfaces/group.js';
+
+// Typescript is annoywith with parameter forwarding from class.ts
+interface GroupParams {
+    classid: string;
+    assignmentid: string;
+    groupid?: string;
+}
+
+export async function getGroupHandler(req: Request<GroupParams>, res: Response): Promise<void> {
+    const classId = req.params.classid;
+    const full = req.query.full === 'true';
+    const assignmentId = +req.params.assignmentid;
+
+    if (isNaN(assignmentId)) {
+        res.status(400).json({ error: 'Assignment id must be a number' });
+        return;
+    }
+
+    const groupId = +req.params.groupid!; // Can't be undefined
+
+    if (isNaN(groupId)) {
+        res.status(400).json({ error: 'Group id must be a number' });
+        return;
+    }
+
+    const group = await getGroup(classId, assignmentId, groupId, full);
+
+    res.json(group);
+}
+
+export async function getAllGroupsHandler(req: Request, res: Response): Promise<void> {
+    const classId = req.params.classid;
+    const full = req.query.full === 'true';
+
+    const assignmentId = +req.params.assignmentid;
+
+    if (isNaN(assignmentId)) {
+        res.status(400).json({ error: 'Assignment id must be a number' });
+        return;
+    }
+
+    const groups = await getAllGroups(classId, assignmentId, full);
+
+    res.json({
+        groups: groups,
+    });
+}
+
+export async function createGroupHandler(req: Request, res: Response): Promise<void> {
+    const classid = req.params.classid;
+    const assignmentId = +req.params.assignmentid;
+
+    if (isNaN(assignmentId)) {
+        res.status(400).json({ error: 'Assignment id must be a number' });
+        return;
+    }
+
+    const groupData = req.body as GroupDTO;
+    const group = await createGroup(groupData, classid, assignmentId);
+
+    if (!group) {
+        res.status(500).json({ error: 'Something went wrong while creating group' });
+        return;
+    }
+
+    res.status(201).json({ group: group });
+}
+
+export async function getGroupSubmissionsHandler(req: Request, res: Response): Promise<void> {
+    const classId = req.params.classid;
+    // Const full = req.query.full === 'true';
+
+    const assignmentId = +req.params.assignmentid;
+
+    if (isNaN(assignmentId)) {
+        res.status(400).json({ error: 'Assignment id must be a number' });
+        return;
+    }
+
+    const groupId = +req.params.groupid!; // Can't be undefined
+
+    if (isNaN(groupId)) {
+        res.status(400).json({ error: 'Group id must be a number' });
+        return;
+    }
+
+    const submissions = await getGroupSubmissions(classId, assignmentId, groupId);
+
+    res.json({
+        submissions: submissions,
+    });
+}
--- a/backend/src/controllers/learningObjects.ts
+++ b/backend/src/controllers/learningObjects.ts
--- a/backend/src/controllers/learningPaths.ts
+++ b/backend/src/controllers/learningPaths.ts
@ -1,45 +0,0 @@
-import { Request, Response } from 'express';
-import { themes } from '../data/themes.js';
-import { FALLBACK_LANG } from '../config.js';
-import { getLogger } from '../logging/initalize.js';
-import learningPathService from '../services/learning-paths/learning-path-service.js';
-import { Language } from '../entities/content/language.js';
-/**
- * Fetch learning paths based on query parameters.
- */
-export async function getLearningPaths(req: Request, res: Response): Promise<void> {
-    try {
-        const hruids = req.query.hruid;
-        const themeKey = req.query.theme as string;
-        const searchQuery = req.query.search as string;
-        const language = (req.query.language as Language) || FALLBACK_LANG;
-
-        let hruidList;
-
-        if (hruids) {
-            hruidList = Array.isArray(hruids) ? hruids.map(String) : [String(hruids)];
-        } else if (themeKey) {
-            const theme = themes.find((t) => t.title === themeKey);
-            if (theme) {
-                hruidList = theme.hruids;
-            } else {
-                res.status(404).json({
-                    error: `Theme "${themeKey}" not found.`,
-                });
-                return;
-            }
-        } else if (searchQuery) {
-            const searchResults = await learningPathService.searchLearningPaths(searchQuery, language);
-            res.json(searchResults);
-            return;
-        } else {
-            hruidList = themes.flatMap((theme) => theme.hruids);
-        }
-
-        const learningPaths = await learningPathService.fetchLearningPaths(hruidList, language, `HRUIDs: ${hruidList.join(', ')}`);
-        res.json(learningPaths.data);
-    } catch (error) {
-        getLogger().error('❌ Unexpected error fetching learning paths:', error);
-        res.status(500).json({ error: 'Internal server error' });
-    }
-}
--- a/backend/src/controllers/questions.ts
+++ b/backend/src/controllers/questions.ts
@ -0,0 +1,119 @@
+import { Request, Response } from 'express';
+import { createQuestion, deleteQuestion, getAllQuestions, getAnswersByQuestion, getQuestion } from '../services/questions.js';
+import { QuestionDTO, QuestionId } from '../interfaces/question.js';
+import { FALLBACK_LANG, FALLBACK_SEQ_NUM } from '../config.js';
+import { LearningObjectIdentifier } from '../entities/content/learning-object-identifier.js';
+import { Language } from '../entities/content/language.js';
+
+function getObjectId(req: Request, res: Response): LearningObjectIdentifier | null {
+    const { hruid, version } = req.params;
+    const lang = req.query.lang;
+
+    if (!hruid || !version) {
+        res.status(400).json({ error: 'Missing required parameters.' });
+        return null;
+    }
+
+    return {
+        hruid,
+        language: (lang as Language) || FALLBACK_LANG,
+        version: +version,
+    };
+}
+
+function getQuestionId(req: Request, res: Response): QuestionId | null {
+    const seq = req.params.seq;
+    const learningObjectIdentifier = getObjectId(req, res);
+
+    if (!learningObjectIdentifier) {
+        return null;
+    }
+
+    return {
+        learningObjectIdentifier,
+        sequenceNumber: seq ? Number(seq) : FALLBACK_SEQ_NUM,
+    };
+}
+
+export async function getAllQuestionsHandler(req: Request, res: Response): Promise<void> {
+    const objectId = getObjectId(req, res);
+    const full = req.query.full === 'true';
+
+    if (!objectId) {
+        return;
+    }
+
+    const questions = await getAllQuestions(objectId, full);
+
+    if (!questions) {
+        res.status(404).json({ error: `Questions not found.` });
+    } else {
+        res.json(questions);
+    }
+}
+
+export async function getQuestionHandler(req: Request, res: Response): Promise<void> {
+    const questionId = getQuestionId(req, res);
+
+    if (!questionId) {
+        return;
+    }
+
+    const question = await getQuestion(questionId);
+
+    if (!question) {
+        res.status(404).json({ error: `Question not found.` });
+    } else {
+        res.json(question);
+    }
+}
+
+export async function getQuestionAnswersHandler(req: Request, res: Response): Promise<void> {
+    const questionId = getQuestionId(req, res);
+    const full = req.query.full === 'true';
+
+    if (!questionId) {
+        return;
+    }
+
+    const answers = getAnswersByQuestion(questionId, full);
+
+    if (!answers) {
+        res.status(404).json({ error: `Questions not found.` });
+    } else {
+        res.json(answers);
+    }
+}
+
+export async function createQuestionHandler(req: Request, res: Response): Promise<void> {
+    const questionDTO = req.body as QuestionDTO;
+
+    if (!questionDTO.learningObjectIdentifier || !questionDTO.author || !questionDTO.content) {
+        res.status(400).json({ error: 'Missing required fields: identifier and content' });
+        return;
+    }
+
+    const question = await createQuestion(questionDTO);
+
+    if (!question) {
+        res.status(400).json({ error: 'Could not add question' });
+    } else {
+        res.json(question);
+    }
+}
+
+export async function deleteQuestionHandler(req: Request, res: Response): Promise<void> {
+    const questionId = getQuestionId(req, res);
+
+    if (!questionId) {
+        return;
+    }
+
+    const question = await deleteQuestion(questionId);
+
+    if (!question) {
+        res.status(400).json({ error: 'Could not find nor delete question' });
+    } else {
+        res.json(question);
+    }
+}
--- a/backend/src/controllers/students.ts
+++ b/backend/src/controllers/students.ts
@ -0,0 +1,146 @@
+import { Request, Response } from 'express';
+import {
+    createStudent,
+    deleteStudent,
+    getAllStudents,
+    getStudent,
+    getStudentAssignments,
+    getStudentClasses,
+    getStudentGroups,
+    getStudentSubmissions,
+} from '../services/students.js';
+import { ClassDTO } from '../interfaces/class.js';
+import { getAllAssignments } from '../services/assignments.js';
+import { getUserHandler } from './users.js';
+import { Student } from '../entities/users/student.entity.js';
+import { StudentDTO } from '../interfaces/student.js';
+import { getStudentRepository } from '../data/repositories.js';
+import { UserDTO } from '../interfaces/user.js';
+
+// TODO: accept arguments (full, ...)
+// TODO: endpoints
+export async function getAllStudentsHandler(req: Request, res: Response): Promise<void> {
+    const full = req.query.full === 'true';
+
+    const studentRepository = getStudentRepository();
+
+    const students: StudentDTO[] | string[] = full ? await getAllStudents() : await getAllStudents();
+
+    if (!students) {
+        res.status(404).json({ error: `Student not found.` });
+        return;
+    }
+
+    res.status(201).json(students);
+}
+
+export async function getStudentHandler(req: Request, res: Response): Promise<void> {
+    const username = req.params.username;
+
+    if (!username) {
+        res.status(400).json({ error: 'Missing required field: username' });
+        return;
+    }
+
+    const user = await getStudent(username);
+
+    if (!user) {
+        res.status(404).json({
+            error: `User with username '${username}' not found.`,
+        });
+        return;
+    }
+
+    res.status(201).json(user);
+}
+
+export async function createStudentHandler(req: Request, res: Response) {
+    const userData = req.body as StudentDTO;
+
+    if (!userData.username || !userData.firstName || !userData.lastName) {
+        res.status(400).json({
+            error: 'Missing required fields: username, firstName, lastName',
+        });
+        return;
+    }
+
+    const newUser = await createStudent(userData);
+    res.status(201).json(newUser);
+}
+
+export async function deleteStudentHandler(req: Request, res: Response) {
+    const username = req.params.username;
+
+    if (!username) {
+        res.status(400).json({ error: 'Missing required field: username' });
+        return;
+    }
+
+    const deletedUser = await deleteStudent(username);
+    if (!deletedUser) {
+        res.status(404).json({
+            error: `User with username '${username}' not found.`,
+        });
+        return;
+    }
+
+    res.status(200).json(deletedUser);
+}
+
+export async function getStudentClassesHandler(req: Request, res: Response): Promise<void> {
+    try {
+        const full = req.query.full === 'true';
+        const username = req.params.id;
+
+        const classes = await getStudentClasses(username, full);
+
+        res.json({
+            classes: classes,
+            endpoints: {
+                self: `${req.baseUrl}/${req.params.id}`,
+                classes: `${req.baseUrl}/${req.params.id}/invitations`,
+                questions: `${req.baseUrl}/${req.params.id}/assignments`,
+                students: `${req.baseUrl}/${req.params.id}/students`,
+            },
+        });
+    } catch (error) {
+        console.error('Error fetching learning objects:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+// TODO
+// Might not be fully correct depending on if
+// A class has an assignment, that all students
+// Have this assignment.
+export async function getStudentAssignmentsHandler(req: Request, res: Response): Promise<void> {
+    const full = req.query.full === 'true';
+    const username = req.params.id;
+
+    const assignments = getStudentAssignments(username, full);
+
+    res.json({
+        assignments: assignments,
+    });
+}
+
+export async function getStudentGroupsHandler(req: Request, res: Response): Promise<void> {
+    const full = req.query.full === 'true';
+    const username = req.params.id;
+
+    const groups = await getStudentGroups(username, full);
+
+    res.json({
+        groups: groups,
+    });
+}
+
+export async function getStudentSubmissionsHandler(req: Request, res: Response): Promise<void> {
+    const username = req.params.id;
+
+    const submissions = await getStudentSubmissions(username);
+
+    res.json({
+        submissions: submissions,
+    });
+}
--- a/backend/src/controllers/submissions.ts
+++ b/backend/src/controllers/submissions.ts
@ -0,0 +1,59 @@
+import { Request, Response } from 'express';
+import { createSubmission, deleteSubmission, getSubmission } from '../services/submissions.js';
+import { Language, languageMap } from '../entities/content/language.js';
+import { SubmissionDTO } from '../interfaces/submission';
+
+interface SubmissionParams {
+    hruid: string;
+    id: number;
+}
+
+export async function getSubmissionHandler(req: Request<SubmissionParams>, res: Response): Promise<void> {
+    const lohruid = req.params.hruid;
+    const submissionNumber = +req.params.id;
+
+    if (isNaN(submissionNumber)) {
+        res.status(400).json({ error: 'Submission number is not a number' });
+        return;
+    }
+
+    const lang = languageMap[req.query.language as string] || Language.Dutch;
+    const version = (req.query.version || 1) as number;
+
+    const submission = await getSubmission(lohruid, lang, version, submissionNumber);
+
+    if (!submission) {
+        res.status(404).json({ error: 'Submission not found' });
+        return;
+    }
+
+    res.json(submission);
+}
+
+export async function createSubmissionHandler(req: Request, res: Response) {
+    const submissionDTO = req.body as SubmissionDTO;
+
+    const submission = await createSubmission(submissionDTO);
+
+    if (!submission) {
+        res.status(404).json({ error: 'Submission not added' });
+    } else {
+        res.json(submission);
+    }
+}
+
+export async function deleteSubmissionHandler(req: Request, res: Response) {
+    const hruid = req.params.hruid;
+    const submissionNumber = +req.params.id;
+
+    const lang = languageMap[req.query.language as string] || Language.Dutch;
+    const version = (req.query.version || 1) as number;
+
+    const submission = await deleteSubmission(hruid, lang, version, submissionNumber);
+
+    if (!submission) {
+        res.status(404).json({ error: 'Submission not found' });
+    } else {
+        res.json(submission);
+    }
+}
--- a/backend/src/controllers/teachers.ts
+++ b/backend/src/controllers/teachers.ts
@ -0,0 +1,144 @@
+import { Request, Response } from 'express';
+import {
+    createTeacher,
+    deleteTeacher,
+    getAllTeachers,
+    getClassesByTeacher,
+    getClassIdsByTeacher,
+    getQuestionIdsByTeacher,
+    getQuestionsByTeacher,
+    getStudentIdsByTeacher,
+    getStudentsByTeacher,
+    getTeacher,
+} from '../services/teachers.js';
+import { ClassDTO } from '../interfaces/class.js';
+import { StudentDTO } from '../interfaces/student.js';
+import { QuestionDTO, QuestionId } from '../interfaces/question.js';
+import { Teacher } from '../entities/users/teacher.entity.js';
+import { TeacherDTO } from '../interfaces/teacher.js';
+import { getTeacherRepository } from '../data/repositories.js';
+
+export async function getAllTeachersHandler(req: Request, res: Response): Promise<void> {
+    const full = req.query.full === 'true';
+
+    const teacherRepository = getTeacherRepository();
+
+    const teachers: TeacherDTO[] | string[] = full ? await getAllTeachers() : await getAllTeachers();
+
+    if (!teachers) {
+        res.status(404).json({ error: `Teacher not found.` });
+        return;
+    }
+
+    res.status(201).json(teachers);
+}
+
+export async function getTeacherHandler(req: Request, res: Response): Promise<void> {
+    const username = req.params.username;
+
+    if (!username) {
+        res.status(400).json({ error: 'Missing required field: username' });
+        return;
+    }
+
+    const user = await getTeacher(username);
+
+    if (!user) {
+        res.status(404).json({
+            error: `User with username '${username}' not found.`,
+        });
+        return;
+    }
+
+    res.status(201).json(user);
+}
+
+export async function createTeacherHandler(req: Request, res: Response) {
+    const userData = req.body as TeacherDTO;
+
+    if (!userData.username || !userData.firstName || !userData.lastName) {
+        res.status(400).json({
+            error: 'Missing required fields: username, firstName, lastName',
+        });
+        return;
+    }
+
+    const newUser = await createTeacher(userData);
+    res.status(201).json(newUser);
+}
+
+export async function deleteTeacherHandler(req: Request, res: Response) {
+    const username = req.params.username;
+
+    if (!username) {
+        res.status(400).json({ error: 'Missing required field: username' });
+        return;
+    }
+
+    const deletedUser = await deleteTeacher(username);
+    if (!deletedUser) {
+        res.status(404).json({
+            error: `User with username '${username}' not found.`,
+        });
+        return;
+    }
+
+    res.status(200).json(deletedUser);
+}
+
+export async function getTeacherClassHandler(req: Request, res: Response): Promise<void> {
+    try {
+        const username = req.params.username as string;
+        const full = req.query.full === 'true';
+
+        if (!username) {
+            res.status(400).json({ error: 'Missing required field: username' });
+            return;
+        }
+
+        const classes: ClassDTO[] | string[] = full ? await getClassesByTeacher(username) : await getClassIdsByTeacher(username);
+
+        res.status(201).json(classes);
+    } catch (error) {
+        console.error('Error fetching classes by teacher:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+export async function getTeacherStudentHandler(req: Request, res: Response): Promise<void> {
+    try {
+        const username = req.params.username as string;
+        const full = req.query.full === 'true';
+
+        if (!username) {
+            res.status(400).json({ error: 'Missing required field: username' });
+            return;
+        }
+
+        const students: StudentDTO[] | string[] = full ? await getStudentsByTeacher(username) : await getStudentIdsByTeacher(username);
+
+        res.status(201).json(students);
+    } catch (error) {
+        console.error('Error fetching students by teacher:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+export async function getTeacherQuestionHandler(req: Request, res: Response): Promise<void> {
+    try {
+        const username = req.params.username as string;
+        const full = req.query.full === 'true';
+
+        if (!username) {
+            res.status(400).json({ error: 'Missing required field: username' });
+            return;
+        }
+
+        const questions: QuestionDTO[] | QuestionId[] = full ? await getQuestionsByTeacher(username) : await getQuestionIdsByTeacher(username);
+
+        res.status(201).json(questions);
+    } catch (error) {
+        console.error('Error fetching questions by teacher:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
--- a/backend/src/controllers/themes.ts
+++ b/backend/src/controllers/themes.ts
@ -1,6 +1,6 @@
 import { Request, Response } from 'express';
 import { themes } from '../data/themes.js';
-import { loadTranslations } from '../util/translationHelper.js';
+import { loadTranslations } from '../util/translation-helper.js';

 interface Translations {
    curricula_page: {
--- a/backend/src/controllers/users.ts
+++ b/backend/src/controllers/users.ts
@ -0,0 +1,91 @@
+import { Request, Response } from 'express';
+import { UserService } from '../services/users.js';
+import { UserDTO } from '../interfaces/user.js';
+import { User } from '../entities/users/user.entity.js';
+
+export async function getAllUsersHandler<T extends User>(req: Request, res: Response, service: UserService<T>): Promise<void> {
+    try {
+        const full = req.query.full === 'true';
+
+        const users: UserDTO[] | string[] = full ? await service.getAllUsers() : await service.getAllUserIds();
+
+        if (!users) {
+            res.status(404).json({ error: `Users not found.` });
+            return;
+        }
+
+        res.status(201).json(users);
+    } catch (error) {
+        console.error('❌ Error fetching users:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+export async function getUserHandler<T extends User>(req: Request, res: Response, service: UserService<T>): Promise<void> {
+    try {
+        const username = req.params.username as string;
+
+        if (!username) {
+            res.status(400).json({ error: 'Missing required field: username' });
+            return;
+        }
+
+        const user = await service.getUserByUsername(username);
+
+        if (!user) {
+            res.status(404).json({
+                error: `User with username '${username}' not found.`,
+            });
+            return;
+        }
+
+        res.status(201).json(user);
+    } catch (error) {
+        console.error('❌ Error fetching users:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+export async function createUserHandler<T extends User>(req: Request, res: Response, service: UserService<T>, UserClass: new () => T) {
+    try {
+        console.log('req', req);
+        const userData = req.body as UserDTO;
+
+        if (!userData.username || !userData.firstName || !userData.lastName) {
+            res.status(400).json({
+                error: 'Missing required fields: username, firstName, lastName',
+            });
+            return;
+        }
+
+        const newUser = await service.createUser(userData, UserClass);
+        res.status(201).json(newUser);
+    } catch (error) {
+        console.error('❌ Error creating user:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
+
+export async function deleteUserHandler<T extends User>(req: Request, res: Response, service: UserService<T>) {
+    try {
+        const username = req.params.username;
+
+        if (!username) {
+            res.status(400).json({ error: 'Missing required field: username' });
+            return;
+        }
+
+        const deletedUser = await service.deleteUser(username);
+        if (!deletedUser) {
+            res.status(404).json({
+                error: `User with username '${username}' not found.`,
+            });
+            return;
+        }
+
+        res.status(200).json(deletedUser);
+    } catch (error) {
+        console.error('❌ Error deleting user:', error);
+        res.status(500).json({ error: 'Internal server error' });
+    }
+}
--- a/backend/src/data/assignments/group-repository.ts
+++ b/backend/src/data/assignments/group-repository.ts
@ -1,16 +1,26 @@
 import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { Group } from '../../entities/assignments/group.entity.js';
 import { Assignment } from '../../entities/assignments/assignment.entity.js';
+import { Student } from '../../entities/users/student.entity.js';

 export class GroupRepository extends DwengoEntityRepository<Group> {
    public findByAssignmentAndGroupNumber(assignment: Assignment, groupNumber: number): Promise<Group | null> {
-        return this.findOne({
-            assignment: assignment,
-            groupNumber: groupNumber,
-        });
+        return this.findOne(
+            {
+                assignment: assignment,
+                groupNumber: groupNumber,
+            },
+            { populate: ['members'] }
+        );
    }
    public findAllGroupsForAssignment(assignment: Assignment): Promise<Group[]> {
-        return this.findAll({ where: { assignment: assignment } });
+        return this.findAll({
+            where: { assignment: assignment },
+            populate: ['members'],
+        });
+    }
+    public findAllGroupsWithStudent(student: Student): Promise<Group[]> {
+        return this.find({ members: student }, { populate: ['members'] });
    }
    public deleteByAssignmentAndGroupNumber(assignment: Assignment, groupNumber: number) {
        return this.deleteWhere({
--- a/backend/src/data/assignments/submission-repository.ts
+++ b/backend/src/data/assignments/submission-repository.ts
@ -38,6 +38,14 @@ export class SubmissionRepository extends DwengoEntityRepository<Submission> {
        );
    }

+    public findAllSubmissionsForGroup(group: Group): Promise<Submission[]> {
+        return this.find({ onBehalfOf: group });
+    }
+
+    public findAllSubmissionsForStudent(student: Student): Promise<Submission[]> {
+        return this.find({ submitter: student });
+    }
+
    public deleteSubmissionByLearningObjectAndSubmissionNumber(loId: LearningObjectIdentifier, submissionNumber: number): Promise<void> {
        return this.deleteWhere({
            learningObjectHruid: loId.hruid,
--- a/backend/src/data/classes/class-repository.ts
+++ b/backend/src/data/classes/class-repository.ts
@ -1,11 +1,23 @@
 import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { Class } from '../../entities/classes/class.entity.js';
+import { Student } from '../../entities/users/student.entity.js';
+import { Teacher } from '../../entities/users/teacher.entity';

 export class ClassRepository extends DwengoEntityRepository<Class> {
    public findById(id: string): Promise<Class | null> {
-        return this.findOne({ classId: id });
+        return this.findOne({ classId: id }, { populate: ['students', 'teachers'] });
    }
    public deleteById(id: string): Promise<void> {
        return this.deleteWhere({ classId: id });
    }
+    public findByStudent(student: Student): Promise<Class[]> {
+        return this.find(
+            { students: student },
+            { populate: ['students', 'teachers'] } // Voegt student en teacher objecten toe
+        );
+    }
+
+    public findByTeacher(teacher: Teacher): Promise<Class[]> {
+        return this.find({ teachers: teacher }, { populate: ['students', 'teachers'] });
+    }
 }
--- a/backend/src/data/content/learning-object-repository.ts
+++ b/backend/src/data/content/learning-object-repository.ts
@ -1,7 +1,8 @@
 import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { LearningObject } from '../../entities/content/learning-object.entity.js';
 import { LearningObjectIdentifier } from '../../entities/content/learning-object-identifier.js';
-import { Language } from '../../entities/content/language';
+import { Language } from '../../entities/content/language.js';
+import { Teacher } from '../../entities/users/teacher.entity.js';

 export class LearningObjectRepository extends DwengoEntityRepository<LearningObject> {
    public findByIdentifier(identifier: LearningObjectIdentifier): Promise<LearningObject | null> {
@ -31,4 +32,11 @@ export class LearningObjectRepository extends DwengoEntityRepository<LearningObj
            }
        );
    }
+
+    public findAllByTeacher(teacher: Teacher): Promise<LearningObject[]> {
+        return this.find(
+            { admins: teacher },
+            { populate: ['admins'] } // Make sure to load admin relations
+        );
+    }
 }
--- a/backend/src/data/questions/question-repository.ts
+++ b/backend/src/data/questions/question-repository.ts
@ -2,6 +2,7 @@ import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { Question } from '../../entities/questions/question.entity.js';
 import { LearningObjectIdentifier } from '../../entities/content/learning-object-identifier.js';
 import { Student } from '../../entities/users/student.entity.js';
+import { LearningObject } from '../../entities/content/learning-object.entity.js';

 export class QuestionRepository extends DwengoEntityRepository<Question> {
    public createQuestion(question: { loId: LearningObjectIdentifier; author: Student; content: string }): Promise<Question> {
@ -40,4 +41,17 @@ export class QuestionRepository extends DwengoEntityRepository<Question> {
            sequenceNumber: sequenceNumber,
        });
    }
+
+    public async findAllByLearningObjects(learningObjects: LearningObject[]): Promise<Question[]> {
+        const objectIdentifiers = learningObjects.map((lo) => ({
+            learningObjectHruid: lo.hruid,
+            learningObjectLanguage: lo.language,
+            learningObjectVersion: lo.version,
+        }));
+
+        return this.findAll({
+            where: { $or: objectIdentifiers },
+            orderBy: { timestamp: 'ASC' },
+        });
+    }
 }
--- a/backend/src/data/repositories.ts
+++ b/backend/src/data/repositories.ts
@ -54,7 +54,6 @@ function repositoryGetter<T extends AnyEntity, R extends EntityRepository<T>>(en
 }

 /* Users */
-export const getUserRepository = repositoryGetter<User, UserRepository>(User);
 export const getStudentRepository = repositoryGetter<Student, StudentRepository>(Student);
 export const getTeacherRepository = repositoryGetter<Teacher, TeacherRepository>(Teacher);

--- a/backend/src/data/users/student-repository.ts
+++ b/backend/src/data/users/student-repository.ts
@ -1,5 +1,9 @@
-import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { Student } from '../../entities/users/student.entity.js';
+import { User } from '../../entities/users/user.entity.js';
+import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
+// Import { UserRepository } from './user-repository.js';
+
+// Export class StudentRepository extends UserRepository<Student> {}

 export class StudentRepository extends DwengoEntityRepository<Student> {
    public findByUsername(username: string): Promise<Student | null> {
--- a/backend/src/data/users/teacher-repository.ts
+++ b/backend/src/data/users/teacher-repository.ts
@ -1,5 +1,6 @@
-import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { Teacher } from '../../entities/users/teacher.entity.js';
+import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
+import { UserRepository } from './user-repository.js';

 export class TeacherRepository extends DwengoEntityRepository<Teacher> {
    public findByUsername(username: string): Promise<Teacher | null> {
--- a/backend/src/data/users/user-repository.ts
+++ b/backend/src/data/users/user-repository.ts
@ -1,11 +1,11 @@
 import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
 import { User } from '../../entities/users/user.entity.js';

-export class UserRepository extends DwengoEntityRepository<User> {
-    public findByUsername(username: string): Promise<User | null> {
-        return this.findOne({ username: username });
+export class UserRepository<T extends User> extends DwengoEntityRepository<T> {
+    public findByUsername(username: string): Promise<T | null> {
+        return this.findOne({ username } as Partial<T>);
    }
    public deleteByUsername(username: string): Promise<void> {
-        return this.deleteWhere({ username: username });
+        return this.deleteWhere({ username } as Partial<T>);
    }
 }
--- a/backend/src/entities/assignments/assignment.entity.ts
+++ b/backend/src/entities/assignments/assignment.entity.ts
@ -1,16 +1,21 @@
-import { Entity, Enum, ManyToOne, OneToMany, PrimaryKey, Property } from '@mikro-orm/core';
+import { Collection, Entity, Enum, ManyToOne, OneToMany, PrimaryKey, Property } from '@mikro-orm/core';
 import { Class } from '../classes/class.entity.js';
 import { Group } from './group.entity.js';
 import { Language } from '../content/language.js';
 import { AssignmentRepository } from '../../data/assignments/assignment-repository.js';

-@Entity({ repository: () => AssignmentRepository })
+@Entity({
+    repository: () => AssignmentRepository,
+})
 export class Assignment {
-    @ManyToOne({ entity: () => Class, primary: true })
+    @ManyToOne({
+        entity: () => Class,
+        primary: true,
+    })
    within!: Class;

-    @PrimaryKey({ type: 'number' })
-    id!: number;
+    @PrimaryKey({ type: 'number', autoincrement: true })
+    id?: number;

    @Property({ type: 'string' })
    title!: string;
@ -21,9 +26,14 @@ export class Assignment {
    @Property({ type: 'string' })
    learningPathHruid!: string;

-    @Enum({ items: () => Language })
+    @Enum({
+        items: () => Language,
+    })
    learningPathLanguage!: Language;

-    @OneToMany({ entity: () => Group, mappedBy: 'assignment' })
+    @OneToMany({
+        entity: () => Group,
+        mappedBy: 'assignment',
+    })
    groups!: Group[];
 }
--- a/backend/src/entities/assignments/group.entity.ts
+++ b/backend/src/entities/assignments/group.entity.ts
@ -1,9 +1,11 @@
-import { Entity, ManyToMany, ManyToOne, PrimaryKey } from '@mikro-orm/core';
+import { Collection, Entity, ManyToMany, ManyToOne, PrimaryKey } from '@mikro-orm/core';
 import { Assignment } from './assignment.entity.js';
 import { Student } from '../users/student.entity.js';
 import { GroupRepository } from '../../data/assignments/group-repository.js';

-@Entity({ repository: () => GroupRepository })
+@Entity({
+    repository: () => GroupRepository,
+})
 export class Group {
    @ManyToOne({
        entity: () => Assignment,
@ -11,8 +13,8 @@ export class Group {
    })
    assignment!: Assignment;

-    @PrimaryKey({ type: 'integer' })
-    groupNumber!: number;
+    @PrimaryKey({ type: 'integer', autoincrement: true })
+    groupNumber?: number;

    @ManyToMany({
        entity: () => Student,
--- a/backend/src/entities/assignments/submission.entity.ts
+++ b/backend/src/entities/assignments/submission.entity.ts
@ -18,7 +18,7 @@ export class Submission {
    @PrimaryKey({ type: 'numeric' })
    learningObjectVersion: number = 1;

-    @PrimaryKey({ type: 'integer' })
+    @PrimaryKey({ type: 'integer', autoincrement: true })
    submissionNumber!: number;

    @ManyToOne({
--- a/backend/src/entities/classes/class-join-request.entity.ts
+++ b/backend/src/entities/classes/class-join-request.entity.ts
@ -3,7 +3,9 @@ import { Student } from '../users/student.entity.js';
 import { Class } from './class.entity.js';
 import { ClassJoinRequestRepository } from '../../data/classes/class-join-request-repository.js';

-@Entity({ repository: () => ClassJoinRequestRepository })
+@Entity({
+    repository: () => ClassJoinRequestRepository,
+})
 export class ClassJoinRequest {
    @ManyToOne({
        entity: () => Student,
--- a/backend/src/entities/classes/class.entity.ts
+++ b/backend/src/entities/classes/class.entity.ts
@ -4,10 +4,12 @@ import { Teacher } from '../users/teacher.entity.js';
 import { Student } from '../users/student.entity.js';
 import { ClassRepository } from '../../data/classes/class-repository.js';

-@Entity({ repository: () => ClassRepository })
+@Entity({
+    repository: () => ClassRepository,
+})
 export class Class {
    @PrimaryKey()
-    classId = v4();
+    classId? = v4();

    @Property({ type: 'string' })
    displayName!: string;
--- a/backend/src/entities/classes/teacher-invitation.entity.ts
+++ b/backend/src/entities/classes/teacher-invitation.entity.ts
@ -7,9 +7,6 @@ import { TeacherInvitationRepository } from '../../data/classes/teacher-invitati
 * Invitation of a teacher into a class (in order to teach it).
 */
@Entity({ repository: () => TeacherInvitationRepository })
-@Entity({
-    repository: () => TeacherInvitationRepository,
-})
 export class TeacherInvitation {
    @ManyToOne({
        entity: () => Teacher,
--- a/backend/src/entities/content/attachment.entity.ts
+++ b/backend/src/entities/content/attachment.entity.ts
@ -2,7 +2,9 @@ import { Entity, ManyToOne, PrimaryKey, Property } from '@mikro-orm/core';
 import { LearningObject } from './learning-object.entity.js';
 import { AttachmentRepository } from '../../data/content/attachment-repository.js';

-@Entity({ repository: () => AttachmentRepository })
+@Entity({
+    repository: () => AttachmentRepository,
+})
 export class Attachment {
    @ManyToOne({
        entity: () => LearningObject,
--- a/backend/src/entities/content/language.ts
+++ b/backend/src/entities/content/language.ts
@ -184,3 +184,10 @@ export enum Language {
    Zhuang = 'za',
    Zulu = 'zu',
 }
+
+export const languageMap: Record<string, Language> = {
+    nl: Language.Dutch,
+    fr: Language.French,
+    en: Language.English,
+    de: Language.German,
+};
--- a/backend/src/interfaces/answer.ts
+++ b/backend/src/interfaces/answer.ts
@ -0,0 +1,38 @@
+import { mapToUserDTO, UserDTO } from './user.js';
+import { mapToQuestionDTO, mapToQuestionId, QuestionDTO, QuestionId } from './question.js';
+import { Answer } from '../entities/questions/answer.entity.js';
+
+export interface AnswerDTO {
+    author: UserDTO;
+    toQuestion: QuestionDTO;
+    sequenceNumber: number;
+    timestamp: string;
+    content: string;
+}
+
+/**
+ * Convert a Question entity to a DTO format.
+ */
+export function mapToAnswerDTO(answer: Answer): AnswerDTO {
+    return {
+        author: mapToUserDTO(answer.author),
+        toQuestion: mapToQuestionDTO(answer.toQuestion),
+        sequenceNumber: answer.sequenceNumber!,
+        timestamp: answer.timestamp.toISOString(),
+        content: answer.content,
+    };
+}
+
+export interface AnswerId {
+    author: string;
+    toQuestion: QuestionId;
+    sequenceNumber: number;
+}
+
+export function mapToAnswerId(answer: AnswerDTO): AnswerId {
+    return {
+        author: answer.author.username,
+        toQuestion: mapToQuestionId(answer.toQuestion),
+        sequenceNumber: answer.sequenceNumber,
+    };
+}
--- a/backend/src/interfaces/assignment.ts
+++ b/backend/src/interfaces/assignment.ts
@ -0,0 +1,52 @@
+import { FALLBACK_LANG } from '../config.js';
+import { Assignment } from '../entities/assignments/assignment.entity.js';
+import { Class } from '../entities/classes/class.entity.js';
+import { languageMap } from '../entities/content/language.js';
+import { GroupDTO, mapToGroupDTO } from './group.js';
+
+export interface AssignmentDTO {
+    id: number;
+    class: string; // Id of class 'within'
+    title: string;
+    description: string;
+    learningPath: string;
+    language: string;
+    groups?: GroupDTO[] | string[]; // TODO
+}
+
+export function mapToAssignmentDTOId(assignment: Assignment): AssignmentDTO {
+    return {
+        id: assignment.id!,
+        class: assignment.within.classId!,
+        title: assignment.title,
+        description: assignment.description,
+        learningPath: assignment.learningPathHruid,
+        language: assignment.learningPathLanguage,
+        // Groups: assignment.groups.map(group => group.groupNumber),
+    };
+}
+
+export function mapToAssignmentDTO(assignment: Assignment): AssignmentDTO {
+    return {
+        id: assignment.id!,
+        class: assignment.within.classId!,
+        title: assignment.title,
+        description: assignment.description,
+        learningPath: assignment.learningPathHruid,
+        language: assignment.learningPathLanguage,
+        // Groups: assignment.groups.map(mapToGroupDTO),
+    };
+}
+
+export function mapToAssignment(assignmentData: AssignmentDTO, cls: Class): Assignment {
+    const assignment = new Assignment();
+    assignment.title = assignmentData.title;
+    assignment.description = assignmentData.description;
+    assignment.learningPathHruid = assignmentData.learningPath;
+    assignment.learningPathLanguage = languageMap[assignmentData.language] || FALLBACK_LANG;
+    assignment.within = cls;
+
+    console.log(assignment);
+
+    return assignment;
+}
--- a/backend/src/interfaces/class.ts
+++ b/backend/src/interfaces/class.ts
@ -0,0 +1,37 @@
+import { Collection } from '@mikro-orm/core';
+import { Class } from '../entities/classes/class.entity.js';
+import { Student } from '../entities/users/student.entity.js';
+import { Teacher } from '../entities/users/teacher.entity.js';
+
+export interface ClassDTO {
+    id: string;
+    displayName: string;
+    teachers: string[];
+    students: string[];
+    joinRequests: string[];
+    endpoints?: {
+        self: string;
+        invitations: string;
+        assignments: string;
+        students: string;
+    };
+}
+
+export function mapToClassDTO(cls: Class): ClassDTO {
+    return {
+        id: cls.classId!,
+        displayName: cls.displayName,
+        teachers: cls.teachers.map((teacher) => teacher.username),
+        students: cls.students.map((student) => student.username),
+        joinRequests: [], // TODO
+    };
+}
+
+export function mapToClass(classData: ClassDTO, students: Collection<Student>, teachers: Collection<Teacher>): Class {
+    const cls = new Class();
+    cls.displayName = classData.displayName;
+    cls.students = students;
+    cls.teachers = teachers;
+
+    return cls;
+}
--- a/backend/src/interfaces/group.ts
+++ b/backend/src/interfaces/group.ts
@ -0,0 +1,25 @@
+import { Group } from '../entities/assignments/group.entity.js';
+import { AssignmentDTO, mapToAssignmentDTO } from './assignment.js';
+import { mapToStudentDTO, StudentDTO } from './student.js';
+
+export interface GroupDTO {
+    assignment: number | AssignmentDTO;
+    groupNumber: number;
+    members: string[] | StudentDTO[];
+}
+
+export function mapToGroupDTO(group: Group): GroupDTO {
+    return {
+        assignment: mapToAssignmentDTO(group.assignment), // ERROR: , group.assignment.within),
+        groupNumber: group.groupNumber!,
+        members: group.members.map(mapToStudentDTO),
+    };
+}
+
+export function mapToGroupDTOId(group: Group): GroupDTO {
+    return {
+        assignment: group.assignment.id!,
+        groupNumber: group.groupNumber!,
+        members: group.members.map((member) => member.username),
+    };
+}
--- a/backend/src/interfaces/list.ts
+++ b/backend/src/interfaces/list.ts
@ -0,0 +1,5 @@
+// TODO: implement something like this but with named endpoints
+export interface List<T> {
+    items: T[];
+    endpoints?: string[];
+}
--- a/backend/src/interfaces/question.ts
+++ b/backend/src/interfaces/question.ts
@ -0,0 +1,44 @@
+import { Question } from '../entities/questions/question.entity.js';
+import { UserDTO } from './user.js';
+import { LearningObjectIdentifier } from '../entities/content/learning-object-identifier.js';
+import { mapToStudentDTO, StudentDTO } from './student.js';
+import { TeacherDTO } from './teacher.js';
+
+export interface QuestionDTO {
+    learningObjectIdentifier: LearningObjectIdentifier;
+    sequenceNumber?: number;
+    author: StudentDTO;
+    timestamp?: string;
+    content: string;
+}
+
+/**
+ * Convert a Question entity to a DTO format.
+ */
+export function mapToQuestionDTO(question: Question): QuestionDTO {
+    const learningObjectIdentifier = {
+        hruid: question.learningObjectHruid,
+        language: question.learningObjectLanguage,
+        version: question.learningObjectVersion,
+    };
+
+    return {
+        learningObjectIdentifier,
+        sequenceNumber: question.sequenceNumber!,
+        author: mapToStudentDTO(question.author),
+        timestamp: question.timestamp.toISOString(),
+        content: question.content,
+    };
+}
+
+export interface QuestionId {
+    learningObjectIdentifier: LearningObjectIdentifier;
+    sequenceNumber: number;
+}
+
+export function mapToQuestionId(question: QuestionDTO): QuestionId {
+    return {
+        learningObjectIdentifier: question.learningObjectIdentifier,
+        sequenceNumber: question.sequenceNumber!,
+    };
+}
--- a/backend/src/interfaces/student.ts
+++ b/backend/src/interfaces/student.ts
@ -0,0 +1,29 @@
+import { Student } from '../entities/users/student.entity.js';
+
+export interface StudentDTO {
+    id: string;
+    username: string;
+    firstName: string;
+    lastName: string;
+    endpoints?: {
+        classes: string;
+        questions: string;
+        invitations: string;
+        groups: string;
+    };
+}
+
+export function mapToStudentDTO(student: Student): StudentDTO {
+    return {
+        id: student.username,
+        username: student.username,
+        firstName: student.firstName,
+        lastName: student.lastName,
+    };
+}
+
+export function mapToStudent(studentData: StudentDTO): Student {
+    const student = new Student(studentData.username, studentData.firstName, studentData.lastName);
+
+    return student;
+}
--- a/backend/src/interfaces/submission.ts
+++ b/backend/src/interfaces/submission.ts
@ -0,0 +1,47 @@
+import { Submission } from '../entities/assignments/submission.entity.js';
+import { Language } from '../entities/content/language.js';
+import { GroupDTO, mapToGroupDTO } from './group.js';
+import { mapToStudent, mapToStudentDTO, StudentDTO } from './student.js';
+import { mapToUser } from './user';
+import { Student } from '../entities/users/student.entity';
+
+export interface SubmissionDTO {
+    learningObjectHruid: string;
+    learningObjectLanguage: Language;
+    learningObjectVersion: number;
+
+    submissionNumber?: number;
+    submitter: StudentDTO;
+    time?: Date;
+    group?: GroupDTO;
+    content: string;
+}
+
+export function mapToSubmissionDTO(submission: Submission): SubmissionDTO {
+    return {
+        learningObjectHruid: submission.learningObjectHruid,
+        learningObjectLanguage: submission.learningObjectLanguage,
+        learningObjectVersion: submission.learningObjectVersion,
+
+        submissionNumber: submission.submissionNumber,
+        submitter: mapToStudentDTO(submission.submitter),
+        time: submission.submissionTime,
+        group: submission.onBehalfOf ? mapToGroupDTO(submission.onBehalfOf) : undefined,
+        content: submission.content,
+    };
+}
+
+export function mapToSubmission(submissionDTO: SubmissionDTO): Submission {
+    const submission = new Submission();
+    submission.learningObjectHruid = submissionDTO.learningObjectHruid;
+    submission.learningObjectLanguage = submissionDTO.learningObjectLanguage;
+    submission.learningObjectVersion = submissionDTO.learningObjectVersion;
+    // Submission.submissionNumber = submissionDTO.submissionNumber;
+    submission.submitter = mapToStudent(submissionDTO.submitter);
+    // Submission.submissionTime = submissionDTO.time;
+    // Submission.onBehalfOf =  submissionDTO.group!;
+    // TODO fix group
+    submission.content = submissionDTO.content;
+
+    return submission;
+}
--- a/backend/src/interfaces/teacher-invitation.ts
+++ b/backend/src/interfaces/teacher-invitation.ts
@ -0,0 +1,25 @@
+import { TeacherInvitation } from '../entities/classes/teacher-invitation.entity.js';
+import { ClassDTO, mapToClassDTO } from './class.js';
+import { mapToUserDTO, UserDTO } from './user.js';
+
+export interface TeacherInvitationDTO {
+    sender: string | UserDTO;
+    receiver: string | UserDTO;
+    class: string | ClassDTO;
+}
+
+export function mapToTeacherInvitationDTO(invitation: TeacherInvitation): TeacherInvitationDTO {
+    return {
+        sender: mapToUserDTO(invitation.sender),
+        receiver: mapToUserDTO(invitation.receiver),
+        class: mapToClassDTO(invitation.class),
+    };
+}
+
+export function mapToTeacherInvitationDTOIds(invitation: TeacherInvitation): TeacherInvitationDTO {
+    return {
+        sender: invitation.sender.username,
+        receiver: invitation.receiver.username,
+        class: invitation.class.classId!,
+    };
+}
--- a/backend/src/interfaces/teacher.ts
+++ b/backend/src/interfaces/teacher.ts
@ -0,0 +1,29 @@
+import { Teacher } from '../entities/users/teacher.entity.js';
+
+export interface TeacherDTO {
+    id: string;
+    username: string;
+    firstName: string;
+    lastName: string;
+    endpoints?: {
+        classes: string;
+        questions: string;
+        invitations: string;
+        groups: string;
+    };
+}
+
+export function mapToTeacherDTO(teacher: Teacher): TeacherDTO {
+    return {
+        id: teacher.username,
+        username: teacher.username,
+        firstName: teacher.firstName,
+        lastName: teacher.lastName,
+    };
+}
+
+export function mapToTeacher(TeacherData: TeacherDTO): Teacher {
+    const teacher = new Teacher(TeacherData.username, TeacherData.firstName, TeacherData.lastName);
+
+    return teacher;
+}
--- a/backend/src/interfaces/user.ts
+++ b/backend/src/interfaces/user.ts
@ -0,0 +1,30 @@
+import { User } from '../entities/users/user.entity.js';
+
+export interface UserDTO {
+    id?: string;
+    username: string;
+    firstName: string;
+    lastName: string;
+    endpoints?: {
+        self: string;
+        classes: string;
+        questions: string;
+        invitations: string;
+    };
+}
+
+export function mapToUserDTO(user: User): UserDTO {
+    return {
+        id: user.username,
+        username: user.username,
+        firstName: user.firstName,
+        lastName: user.lastName,
+    };
+}
+
+export function mapToUser<T extends User>(userData: UserDTO, userInstance: T): T {
+    userInstance.username = userData.username;
+    userInstance.firstName = userData.firstName;
+    userInstance.lastName = userData.lastName;
+    return userInstance;
+}
--- a/backend/src/routes/assignment.ts
+++ b/backend/src/routes/assignment.ts
@ -1,45 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        assignments: ['0', '1'],
-    });
-});
-
-// Information about an assignment with id 'id'
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        title: 'Dit is een test assignment',
-        description: 'Een korte beschrijving',
-        groups: ['0'],
-        learningPath: '0',
-        class: '0',
-        links: {
-            self: `${req.baseUrl}/${req.params.id}`,
-            submissions: `${req.baseUrl}/${req.params.id}`,
-        },
-    });
-});
-
-router.get('/:id/submissions', (req, res) => {
-    res.json({
-        submissions: ['0'],
-    });
-});
-
-router.get('/:id/groups', (req, res) => {
-    res.json({
-        groups: ['0'],
-    });
-});
-
-router.get('/:id/questions', (req, res) => {
-    res.json({
-        questions: ['0'],
-    });
-});
-
-export default router;
--- a/backend/src/routes/assignments.ts
+++ b/backend/src/routes/assignments.ts
@ -0,0 +1,30 @@
+import express from 'express';
+import {
+    createAssignmentHandler,
+    getAllAssignmentsHandler,
+    getAssignmentHandler,
+    getAssignmentsSubmissionsHandler,
+} from '../controllers/assignments.js';
+import groupRouter from './groups.js';
+
+const router = express.Router({ mergeParams: true });
+
+// Root endpoint used to search objects
+router.get('/', getAllAssignmentsHandler);
+
+router.post('/', createAssignmentHandler);
+
+// Information about an assignment with id 'id'
+router.get('/:id', getAssignmentHandler);
+
+router.get('/:id/submissions', getAssignmentsSubmissionsHandler);
+
+router.get('/:id/questions', (req, res) => {
+    res.json({
+        questions: ['0'],
+    });
+});
+
+router.use('/:assignmentid/groups', groupRouter);
+
+export default router;
--- a/backend/src/routes/class.ts
+++ b/backend/src/routes/class.ts
@ -1,46 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        classes: ['0', '1'],
-    });
-});
-
-// Information about an class with id 'id'
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        displayName: 'Klas 4B',
-        teachers: ['0'],
-        students: ['0'],
-        joinRequests: ['0'],
-        links: {
-            self: `${req.baseUrl}/${req.params.id}`,
-            classes: `${req.baseUrl}/${req.params.id}/invitations`,
-            questions: `${req.baseUrl}/${req.params.id}/assignments`,
-            students: `${req.baseUrl}/${req.params.id}/students`,
-        },
-    });
-});
-
-router.get('/:id/invitations', (req, res) => {
-    res.json({
-        invitations: ['0'],
-    });
-});
-
-router.get('/:id/assignments', (req, res) => {
-    res.json({
-        assignments: ['0'],
-    });
-});
-
-router.get('/:id/students', (req, res) => {
-    res.json({
-        students: ['0'],
-    });
-});
-
-export default router;
--- a/backend/src/routes/classes.ts
+++ b/backend/src/routes/classes.ts
@ -0,0 +1,27 @@
+import express from 'express';
+import {
+    createClassHandler,
+    getAllClassesHandler,
+    getClassHandler,
+    getClassStudentsHandler,
+    getTeacherInvitationsHandler,
+} from '../controllers/classes.js';
+import assignmentRouter from './assignments.js';
+
+const router = express.Router();
+
+// Root endpoint used to search objects
+router.get('/', getAllClassesHandler);
+
+router.post('/', createClassHandler);
+
+// Information about an class with id 'id'
+router.get('/:id', getClassHandler);
+
+router.get('/:id/teacher-invitations', getTeacherInvitationsHandler);
+
+router.get('/:id/students', getClassStudentsHandler);
+
+router.use('/:classid/assignments', assignmentRouter);
+
+export default router;
--- a/backend/src/routes/group.ts
+++ b/backend/src/routes/group.ts
@ -1,31 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        groups: ['0', '1'],
-    });
-});
-
-// Information about a group (members, ... [TODO DOC])
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        assignment: '0',
-        students: ['0'],
-        submissions: ['0'],
-        // Reference to other endpoint
-        // Should be less hardcoded
-        questions: `/group/${req.params.id}/question`,
-    });
-});
-
-// The list of questions a group has made
-router.get('/:id/question', (req, res) => {
-    res.json({
-        questions: ['0'],
-    });
-});
-
-export default router;
--- a/backend/src/routes/groups.ts
+++ b/backend/src/routes/groups.ts
@ -0,0 +1,23 @@
+import express from 'express';
+import { createGroupHandler, getAllGroupsHandler, getGroupHandler, getGroupSubmissionsHandler } from '../controllers/groups.js';
+
+const router = express.Router({ mergeParams: true });
+
+// Root endpoint used to search objects
+router.get('/', getAllGroupsHandler);
+
+router.post('/', createGroupHandler);
+
+// Information about a group (members, ... [TODO DOC])
+router.get('/:groupid', getGroupHandler);
+
+router.get('/:groupid', getGroupSubmissionsHandler);
+
+// The list of questions a group has made
+router.get('/:id/questions', (req, res) => {
+    res.json({
+        questions: ['0'],
+    });
+});
+
+export default router;
--- a/backend/src/routes/learning-objects.ts
+++ b/backend/src/routes/learning-objects.ts
@ -1,6 +1,9 @@
 import express from 'express';
 import { getAllLearningObjects, getAttachment, getLearningObject, getLearningObjectHTML } from '../controllers/learning-objects.js';

+import submissionRoutes from './submissions.js';
+import questionRoutes from './questions.js';
+
 const router = express.Router();

 // DWENGO learning objects
@ -21,6 +24,10 @@ router.get('/', getAllLearningObjects);
 // Example: http://localhost:3000/learningObject/un_ai7
 router.get('/:hruid', getLearningObject);

+router.use('/:hruid/submissions', submissionRoutes);
+
+router.use('/:hruid/:version/questions', questionRoutes);
+
 // Parameter: hruid of learning object
 // Query: language, version (optional)
 // Route to fetch the HTML rendering of one learning object based on its hruid.
--- a/backend/src/routes/question.ts
+++ b/backend/src/routes/question.ts
@ -1,33 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        questions: ['0', '1'],
-    });
-});
-
-// Information about an question with id 'id'
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        student: '0',
-        group: '0',
-        time: new Date(2025, 1, 1),
-        content: 'Zijn alle gehele getallen groter dan 2 gelijk aan de som van 2 priemgetallen????',
-        learningObject: '0',
-        links: {
-            self: `${req.baseUrl}/${req.params.id}`,
-            answers: `${req.baseUrl}/${req.params.id}/answers`,
-        },
-    });
-});
-
-router.get('/:id/answers', (req, res) => {
-    res.json({
-        answers: ['0'],
-    });
-});
-
-export default router;
--- a/backend/src/routes/questions.ts
+++ b/backend/src/routes/questions.ts
@ -0,0 +1,25 @@
+import express from 'express';
+import {
+    createQuestionHandler,
+    deleteQuestionHandler,
+    getAllQuestionsHandler,
+    getQuestionAnswersHandler,
+    getQuestionHandler,
+} from '../controllers/questions.js';
+const router = express.Router({ mergeParams: true });
+
+// Query language
+
+// Root endpoint used to search objects
+router.get('/', getAllQuestionsHandler);
+
+router.post('/', createQuestionHandler);
+
+router.delete('/:seq', deleteQuestionHandler);
+
+// Information about a question with id
+router.get('/:seq', getQuestionHandler);
+
+router.get('/answers/:seq', getQuestionAnswersHandler);
+
+export default router;
--- a/backend/src/routes/student.ts
+++ b/backend/src/routes/student.ts
@ -1,55 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        students: ['0', '1'],
-    });
-});
-
-// Information about a student's profile
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        firstName: 'Jimmy',
-        lastName: 'Faster',
-        username: 'JimmyFaster2',
-        endpoints: {
-            classes: `/student/${req.params.id}/classes`,
-            questions: `/student/${req.params.id}/submissions`,
-            invitations: `/student/${req.params.id}/assignments`,
-            groups: `/student/${req.params.id}/groups`,
-        },
-    });
-});
-
-// The list of classes a student is in
-router.get('/:id/classes', (req, res) => {
-    res.json({
-        classes: ['0'],
-    });
-});
-
-// The list of submissions a student has made
-router.get('/:id/submissions', (req, res) => {
-    res.json({
-        submissions: ['0'],
-    });
-});
-
-// The list of assignments a student has
-router.get('/:id/assignments', (req, res) => {
-    res.json({
-        assignments: ['0'],
-    });
-});
-
-// The list of groups a student is in
-router.get('/:id/groups', (req, res) => {
-    res.json({
-        groups: ['0'],
-    });
-});
-
-export default router;
--- a/backend/src/routes/students.ts
+++ b/backend/src/routes/students.ts
@ -0,0 +1,46 @@
+import express from 'express';
+import {
+    createStudentHandler,
+    deleteStudentHandler,
+    getAllStudentsHandler,
+    getStudentAssignmentsHandler,
+    getStudentClassesHandler,
+    getStudentGroupsHandler,
+    getStudentHandler,
+    getStudentSubmissionsHandler,
+} from '../controllers/students.js';
+import { getStudentGroups } from '../services/students.js';
+const router = express.Router();
+
+// Root endpoint used to search objects
+router.get('/', getAllStudentsHandler);
+
+router.post('/', createStudentHandler);
+
+router.delete('/', deleteStudentHandler);
+
+router.delete('/:username', deleteStudentHandler);
+
+// Information about a student's profile
+router.get('/:username', getStudentHandler);
+
+// The list of classes a student is in
+router.get('/:id/classes', getStudentClassesHandler);
+
+// The list of submissions a student has made
+router.get('/:id/submissions', getStudentSubmissionsHandler);
+
+// The list of assignments a student has
+router.get('/:id/assignments', getStudentAssignmentsHandler);
+
+// The list of groups a student is in
+router.get('/:id/groups', getStudentGroupsHandler);
+
+// A list of questions a user has created
+router.get('/:id/questions', (req, res) => {
+    res.json({
+        questions: ['0'],
+    });
+});
+
+export default router;
--- a/backend/src/routes/submission.ts
+++ b/backend/src/routes/submission.ts
@ -1,23 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        submissions: ['0', '1'],
-    });
-});
-
-// Information about an submission with id 'id'
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        student: '0',
-        group: '0',
-        time: new Date(2025, 1, 1),
-        content: 'Wortel 2 is rationeel',
-        learningObject: '0',
-    });
-});
-
-export default router;
--- a/backend/src/routes/submissions.ts
+++ b/backend/src/routes/submissions.ts
@ -0,0 +1,19 @@
+import express from 'express';
+import { createSubmissionHandler, deleteSubmissionHandler, getSubmissionHandler } from '../controllers/submissions.js';
+const router = express.Router({ mergeParams: true });
+
+// Root endpoint used to search objects
+router.get('/', (req, res) => {
+    res.json({
+        submissions: ['0', '1'],
+    });
+});
+
+router.post('/:id', createSubmissionHandler);
+
+// Information about an submission with id 'id'
+router.get('/:id', getSubmissionHandler);
+
+router.delete('/:id', deleteSubmissionHandler);
+
+export default router;
--- a/backend/src/routes/teacher.ts
+++ b/backend/src/routes/teacher.ts
@ -1,48 +0,0 @@
-import express from 'express';
-const router = express.Router();
-
-// Root endpoint used to search objects
-router.get('/', (req, res) => {
-    res.json({
-        teachers: ['0', '1'],
-    });
-});
-
-// Information about a teacher
-router.get('/:id', (req, res) => {
-    res.json({
-        id: req.params.id,
-        firstName: 'John',
-        lastName: 'Doe',
-        username: 'JohnDoe1',
-        links: {
-            self: `${req.baseUrl}/${req.params.id}`,
-            classes: `${req.baseUrl}/${req.params.id}/classes`,
-            questions: `${req.baseUrl}/${req.params.id}/questions`,
-            invitations: `${req.baseUrl}/${req.params.id}/invitations`,
-        },
-    });
-});
-
-// The questions students asked a teacher
-router.get('/:id/questions', (req, res) => {
-    res.json({
-        questions: ['0'],
-    });
-});
-
-// Invitations to other classes a teacher received
-router.get('/:id/invitations', (req, res) => {
-    res.json({
-        invitations: ['0'],
-    });
-});
-
-// A list with ids of classes a teacher is in
-router.get('/:id/classes', (req, res) => {
-    res.json({
-        classes: ['0'],
-    });
-});
-
-export default router;
--- a/backend/src/routes/teachers.ts
+++ b/backend/src/routes/teachers.ts
@ -0,0 +1,37 @@
+import express from 'express';
+import {
+    createTeacherHandler,
+    deleteTeacherHandler,
+    getAllTeachersHandler,
+    getTeacherClassHandler,
+    getTeacherHandler,
+    getTeacherQuestionHandler,
+    getTeacherStudentHandler,
+} from '../controllers/teachers.js';
+const router = express.Router();
+
+// Root endpoint used to search objects
+router.get('/', getAllTeachersHandler);
+
+router.post('/', createTeacherHandler);
+
+router.delete('/', deleteTeacherHandler);
+
+router.get('/:username', getTeacherHandler);
+
+router.delete('/:username', deleteTeacherHandler);
+
+router.get('/:username/classes', getTeacherClassHandler);
+
+router.get('/:username/students', getTeacherStudentHandler);
+
+router.get('/:username/questions', getTeacherQuestionHandler);
+
+// Invitations to other classes a teacher received
+router.get('/:id/invitations', (req, res) => {
+    res.json({
+        invitations: ['0'],
+    });
+});
+
+export default router;
--- a/backend/src/services/assignments.ts
+++ b/backend/src/services/assignments.ts
@ -0,0 +1,85 @@
+import { getAssignmentRepository, getClassRepository, getGroupRepository, getSubmissionRepository } from '../data/repositories.js';
+import { Assignment } from '../entities/assignments/assignment.entity.js';
+import { AssignmentDTO, mapToAssignment, mapToAssignmentDTO, mapToAssignmentDTOId } from '../interfaces/assignment.js';
+import { mapToSubmissionDTO, SubmissionDTO } from '../interfaces/submission.js';
+
+export async function getAllAssignments(classid: string, full: boolean): Promise<AssignmentDTO[]> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classid);
+
+    if (!cls) {
+        return [];
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignments = await assignmentRepository.findAllAssignmentsInClass(cls);
+
+    if (full) {
+        return assignments.map(mapToAssignmentDTO);
+    }
+
+    return assignments.map(mapToAssignmentDTOId);
+}
+
+export async function createAssignment(classid: string, assignmentData: AssignmentDTO): Promise<Assignment | null> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classid);
+
+    if (!cls) {
+        return null;
+    }
+
+    const assignment = mapToAssignment(assignmentData, cls);
+    const assignmentRepository = getAssignmentRepository();
+
+    try {
+        const newAssignment = assignmentRepository.create(assignment);
+        await assignmentRepository.save(newAssignment);
+
+        return newAssignment;
+    } catch (e) {
+        return null;
+    }
+}
+
+export async function getAssignment(classid: string, id: number): Promise<AssignmentDTO | null> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classid);
+
+    if (!cls) {
+        return null;
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignment = await assignmentRepository.findByClassAndId(cls, id);
+
+    if (!assignment) {
+        return null;
+    }
+
+    return mapToAssignmentDTO(assignment);
+}
+
+export async function getAssignmentsSubmissions(classid: string, assignmentNumber: number): Promise<SubmissionDTO[]> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classid);
+
+    if (!cls) {
+        return [];
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignment = await assignmentRepository.findByClassAndId(cls, assignmentNumber);
+
+    if (!assignment) {
+        return [];
+    }
+
+    const groupRepository = getGroupRepository();
+    const groups = await groupRepository.findAllGroupsForAssignment(assignment);
+
+    const submissionRepository = getSubmissionRepository();
+    const submissions = (await Promise.all(groups.map((group) => submissionRepository.findAllSubmissionsForGroup(group)))).flat();
+
+    return submissions.map(mapToSubmissionDTO);
+}
--- a/backend/src/services/class.ts
+++ b/backend/src/services/class.ts
@ -0,0 +1,99 @@
+import { getClassRepository, getStudentRepository, getTeacherInvitationRepository, getTeacherRepository } from '../data/repositories.js';
+import { Class } from '../entities/classes/class.entity.js';
+import { ClassDTO, mapToClassDTO } from '../interfaces/class.js';
+import { mapToStudentDTO, StudentDTO } from '../interfaces/student.js';
+import { mapToTeacherInvitationDTO, mapToTeacherInvitationDTOIds, TeacherInvitationDTO } from '../interfaces/teacher-invitation.js';
+import { getLogger } from '../logging/initalize';
+
+const logger = getLogger();
+
+export async function getAllClasses(full: boolean): Promise<ClassDTO[] | string[]> {
+    const classRepository = getClassRepository();
+    const classes = await classRepository.find({}, { populate: ['students', 'teachers'] });
+
+    if (!classes) {
+        return [];
+    }
+
+    if (full) {
+        return classes.map(mapToClassDTO);
+    }
+    return classes.map((cls) => cls.classId!);
+}
+
+export async function createClass(classData: ClassDTO): Promise<Class | null> {
+    const teacherRepository = getTeacherRepository();
+    const teacherUsernames = classData.teachers || [];
+    const teachers = (await Promise.all(teacherUsernames.map((id) => teacherRepository.findByUsername(id)))).filter((teacher) => teacher != null);
+
+    const studentRepository = getStudentRepository();
+    const studentUsernames = classData.students || [];
+    const students = (await Promise.all(studentUsernames.map((id) => studentRepository.findByUsername(id)))).filter((student) => student != null);
+
+    //Const cls = mapToClass(classData, teachers, students);
+
+    const classRepository = getClassRepository();
+
+    try {
+        const newClass = classRepository.create({
+            displayName: classData.displayName,
+            teachers: teachers,
+            students: students,
+        });
+        await classRepository.save(newClass);
+
+        return newClass;
+    } catch (e) {
+        logger.error(e);
+        return null;
+    }
+}
+
+export async function getClass(classId: string): Promise<ClassDTO | null> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classId);
+
+    if (!cls) {
+        return null;
+    }
+
+    return mapToClassDTO(cls);
+}
+
+async function fetchClassStudents(classId: string): Promise<StudentDTO[]> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classId);
+
+    if (!cls) {
+        return [];
+    }
+
+    return cls.students.map(mapToStudentDTO);
+}
+
+export async function getClassStudents(classId: string): Promise<StudentDTO[]> {
+    return await fetchClassStudents(classId);
+}
+
+export async function getClassStudentsIds(classId: string): Promise<string[]> {
+    const students: StudentDTO[] = await fetchClassStudents(classId);
+    return students.map((student) => student.username);
+}
+
+export async function getClassTeacherInvitations(classId: string, full: boolean): Promise<TeacherInvitationDTO[]> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classId);
+
+    if (!cls) {
+        return [];
+    }
+
+    const teacherInvitationRepository = getTeacherInvitationRepository();
+    const invitations = await teacherInvitationRepository.findAllInvitationsForClass(cls);
+
+    if (full) {
+        return invitations.map(mapToTeacherInvitationDTO);
+    }
+
+    return invitations.map(mapToTeacherInvitationDTOIds);
+}
--- a/backend/src/services/groups.ts
+++ b/backend/src/services/groups.ts
@ -0,0 +1,132 @@
+import { GroupRepository } from '../data/assignments/group-repository.js';
+import {
+    getAssignmentRepository,
+    getClassRepository,
+    getGroupRepository,
+    getStudentRepository,
+    getSubmissionRepository,
+} from '../data/repositories.js';
+import { Group } from '../entities/assignments/group.entity.js';
+import { GroupDTO, mapToGroupDTO, mapToGroupDTOId } from '../interfaces/group.js';
+import { mapToSubmissionDTO, SubmissionDTO } from '../interfaces/submission.js';
+
+export async function getGroup(classId: string, assignmentNumber: number, groupNumber: number, full: boolean): Promise<GroupDTO | null> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classId);
+
+    if (!cls) {
+        return null;
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignment = await assignmentRepository.findByClassAndId(cls, assignmentNumber);
+
+    if (!assignment) {
+        return null;
+    }
+
+    const groupRepository = getGroupRepository();
+    const group = await groupRepository.findByAssignmentAndGroupNumber(assignment, groupNumber);
+
+    if (!group) {
+        return null;
+    }
+
+    if (full) {
+        return mapToGroupDTO(group);
+    }
+
+    return mapToGroupDTOId(group);
+}
+
+export async function createGroup(groupData: GroupDTO, classid: string, assignmentNumber: number): Promise<Group | null> {
+    const studentRepository = getStudentRepository();
+
+    const memberUsernames = (groupData.members as string[]) || []; // TODO check if groupdata.members is a list
+    const members = (await Promise.all([...memberUsernames].map((id) => studentRepository.findByUsername(id)))).filter((student) => student != null);
+
+    console.log(members);
+
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classid);
+
+    if (!cls) {
+        return null;
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignment = await assignmentRepository.findByClassAndId(cls, assignmentNumber);
+
+    if (!assignment) {
+        return null;
+    }
+
+    const groupRepository = getGroupRepository();
+    try {
+        const newGroup = groupRepository.create({
+            assignment: assignment,
+            members: members,
+        });
+        await groupRepository.save(newGroup);
+
+        return newGroup;
+    } catch (e) {
+        console.log(e);
+        return null;
+    }
+}
+
+export async function getAllGroups(classId: string, assignmentNumber: number, full: boolean): Promise<GroupDTO[]> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classId);
+
+    if (!cls) {
+        return [];
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignment = await assignmentRepository.findByClassAndId(cls, assignmentNumber);
+
+    if (!assignment) {
+        return [];
+    }
+
+    const groupRepository = getGroupRepository();
+    const groups = await groupRepository.findAllGroupsForAssignment(assignment);
+
+    if (full) {
+        console.log('full');
+        console.log(groups);
+        return groups.map(mapToGroupDTO);
+    }
+
+    return groups.map(mapToGroupDTOId);
+}
+
+export async function getGroupSubmissions(classId: string, assignmentNumber: number, groupNumber: number): Promise<SubmissionDTO[]> {
+    const classRepository = getClassRepository();
+    const cls = await classRepository.findById(classId);
+
+    if (!cls) {
+        return [];
+    }
+
+    const assignmentRepository = getAssignmentRepository();
+    const assignment = await assignmentRepository.findByClassAndId(cls, assignmentNumber);
+
+    if (!assignment) {
+        return [];
+    }
+
+    const groupRepository = getGroupRepository();
+    const group = await groupRepository.findByAssignmentAndGroupNumber(assignment, groupNumber);
+
+    if (!group) {
+        return [];
+    }
+
+    const submissionRepository = getSubmissionRepository();
+    const submissions = await submissionRepository.findAllSubmissionsForGroup(group);
+
+    return submissions.map(mapToSubmissionDTO);
+}
--- a/backend/src/services/learning-objects.ts
+++ b/backend/src/services/learning-objects.ts
@ -0,0 +1,90 @@
+import { DWENGO_API_BASE } from '../config.js';
+import { fetchWithLogging } from '../util/api-helper.js';
+import { FilteredLearningObject, LearningObjectMetadata, LearningObjectNode, LearningPathResponse } from '../interfaces/learning-content.js';
+
+function filterData(data: LearningObjectMetadata, htmlUrl: string): FilteredLearningObject {
+    return {
+        key: data.hruid, // Hruid learningObject (not path)
+        _id: data._id,
+        uuid: data.uuid,
+        version: data.version,
+        title: data.title,
+        htmlUrl, // Url to fetch html content
+        language: data.language,
+        difficulty: data.difficulty,
+        estimatedTime: data.estimated_time,
+        available: data.available,
+        teacherExclusive: data.teacher_exclusive,
+        educationalGoals: data.educational_goals, // List with learningObjects
+        keywords: data.keywords, // For search
+        description: data.description, // For search (not an actual description)
+        targetAges: data.target_ages,
+        contentType: data.content_type, // Markdown, image, audio, etc.
+        contentLocation: data.content_location, // If content type extern
+        skosConcepts: data.skos_concepts,
+        returnValue: data.return_value, // Callback response information
+    };
+}
+
+/**
+ * Fetches a single learning object by its HRUID
+ */
+export async function getLearningObjectById(hruid: string, language: string): Promise<FilteredLearningObject | null> {
+    const metadataUrl = `${DWENGO_API_BASE}/learningObject/getMetadata?hruid=${hruid}&language=${language}`;
+    const metadata = await fetchWithLogging<LearningObjectMetadata>(
+        metadataUrl,
+        `Metadata for Learning Object HRUID "${hruid}" (language ${language})`
+    );
+
+    if (!metadata) {
+        console.error(`⚠️ WARNING: Learning object "${hruid}" not found.`);
+        return null;
+    }
+
+    const htmlUrl = `${DWENGO_API_BASE}/learningObject/getRaw?hruid=${hruid}&language=${language}`;
+    return filterData(metadata, htmlUrl);
+}
+
+/**
+ * Generic function to fetch learning objects (full data or just HRUIDs)
+ */
+async function fetchLearningObjects(hruid: string, full: boolean, language: string): Promise<FilteredLearningObject[] | string[]> {
+    try {
+        const learningPathResponse: LearningPathResponse = await fetchLearningPaths([hruid], language, `Learning path for HRUID "${hruid}"`);
+
+        if (!learningPathResponse.success || !learningPathResponse.data?.length) {
+            console.error(`⚠️ WARNING: Learning path "${hruid}" exists but contains no learning objects.`);
+            return [];
+        }
+
+        const nodes: LearningObjectNode[] = learningPathResponse.data[0].nodes;
+
+        if (!full) {
+            return nodes.map((node) => node.learningobject_hruid);
+        }
+
+        return await Promise.all(nodes.map(async (node) => getLearningObjectById(node.learningobject_hruid, language))).then((objects) =>
+            objects.filter((obj): obj is FilteredLearningObject => obj !== null)
+        );
+    } catch (error) {
+        console.error('❌ Error fetching learning objects:', error);
+        return [];
+    }
+}
+
+/**
+ * Fetch full learning object data (metadata)
+ */
+export async function getLearningObjectsFromPath(hruid: string, language: string): Promise<FilteredLearningObject[]> {
+    return (await fetchLearningObjects(hruid, true, language)) as FilteredLearningObject[];
+}
+
+/**
+ * Fetch only learning object HRUIDs
+ */
+export async function getLearningObjectIdsFromPath(hruid: string, language: string): Promise<string[]> {
+    return (await fetchLearningObjects(hruid, false, language)) as string[];
+}
+function fetchLearningPaths(arg0: string[], language: string, arg2: string): LearningPathResponse | PromiseLike<LearningPathResponse> {
+    throw new Error('Function not implemented.');
+}
--- a/backend/src/services/learning-objects/dwengo-api-learning-object-provider.ts
+++ b/backend/src/services/learning-objects/dwengo-api-learning-object-provider.ts
@ -1,5 +1,5 @@
 import { DWENGO_API_BASE } from '../../config.js';
-import { fetchWithLogging } from '../../util/apiHelper.js';
+import { fetchWithLogging } from '../../util/api-helper.js';
 import {
    FilteredLearningObject,
    LearningObjectIdentifier,
--- a/backend/src/services/learning-paths/database-learning-path-provider.ts
+++ b/backend/src/services/learning-paths/database-learning-path-provider.ts
@ -29,7 +29,7 @@ async function getLearningObjectsForNodes(nodes: LearningPathNode[]): Promise<Ma
            )
        )
    );
-    if (nullableNodesToLearningObjects.values().some((it) => it === null)) {
+    if (Array.from(nullableNodesToLearningObjects.values()).some((it) => it === null)) {
        throw new Error('At least one of the learning objects on this path could not be found.');
    }
    return nullableNodesToLearningObjects as Map<LearningPathNode, FilteredLearningObject>;
@ -41,15 +41,9 @@ async function getLearningObjectsForNodes(nodes: LearningPathNode[]): Promise<Ma
 async function convertLearningPath(learningPath: LearningPathEntity, order: number, personalizedFor?: PersonalizationTarget): Promise<LearningPath> {
    const nodesToLearningObjects: Map<LearningPathNode, FilteredLearningObject> = await getLearningObjectsForNodes(learningPath.nodes);

-    const targetAges = nodesToLearningObjects
-        .values()
-        .flatMap((it) => it.targetAges || [])
-        .toArray();
+    const targetAges = Array.from(nodesToLearningObjects.values()).flatMap((it) => it.targetAges || []);

-    const keywords = nodesToLearningObjects
-        .values()
-        .flatMap((it) => it.keywords || [])
-        .toArray();
+    const keywords = Array.from(nodesToLearningObjects.values()).flatMap((it) => it.keywords || []);

    const image = learningPath.image ? learningPath.image.toString('base64') : undefined;

@ -83,27 +77,24 @@ async function convertNodes(
    nodesToLearningObjects: Map<LearningPathNode, FilteredLearningObject>,
    personalizedFor?: PersonalizationTarget
 ): Promise<LearningObjectNode[]> {
-    const nodesPromise = nodesToLearningObjects
-        .entries()
-        .map(async (entry) => {
-            const [node, learningObject] = entry;
-            const lastSubmission = personalizedFor ? await getLastSubmissionForCustomizationTarget(node, personalizedFor) : null;
-            return {
-                _id: learningObject.uuid,
-                language: learningObject.language,
-                start_node: node.startNode,
-                created_at: node.createdAt.toISOString(),
-                updatedAt: node.updatedAt.toISOString(),
-                learningobject_hruid: node.learningObjectHruid,
-                version: learningObject.version,
-                transitions: node.transitions
-                    .filter(
-                        (trans) => !personalizedFor || isTransitionPossible(trans, optionalJsonStringToObject(lastSubmission?.content)) // If we want a personalized learning path, remove all transitions that aren't possible.
-                    )
-                    .map((trans, i) => convertTransition(trans, i, nodesToLearningObjects)), // Then convert all the transition
-            };
-        })
-        .toArray();
+    const nodesPromise = Array.from(nodesToLearningObjects.entries()).map(async (entry) => {
+        const [node, learningObject] = entry;
+        const lastSubmission = personalizedFor ? await getLastSubmissionForCustomizationTarget(node, personalizedFor) : null;
+        return {
+            _id: learningObject.uuid,
+            language: learningObject.language,
+            start_node: node.startNode,
+            created_at: node.createdAt.toISOString(),
+            updatedAt: node.updatedAt.toISOString(),
+            learningobject_hruid: node.learningObjectHruid,
+            version: learningObject.version,
+            transitions: node.transitions
+                .filter(
+                    (trans) => !personalizedFor || isTransitionPossible(trans, optionalJsonStringToObject(lastSubmission?.content)) // If we want a personalized learning path, remove all transitions that aren't possible.
+                )
+                .map((trans, i) => convertTransition(trans, i, nodesToLearningObjects)), // Then convert all the transition
+        };
+    });
    return await Promise.all(nodesPromise);
 }

--- a/backend/src/services/learning-paths/dwengo-api-learning-path-provider.ts
+++ b/backend/src/services/learning-paths/dwengo-api-learning-path-provider.ts
@ -1,4 +1,4 @@
-import { fetchWithLogging } from '../../util/apiHelper.js';
+import { fetchWithLogging } from '../../util/api-helper.js';
 import { DWENGO_API_BASE } from '../../config.js';
 import { LearningPath, LearningPathResponse } from '../../interfaces/learning-content.js';
 import { LearningPathProvider } from './learning-path-provider.js';
--- a/backend/src/services/questions.ts
+++ b/backend/src/services/questions.ts
@ -0,0 +1,107 @@
+import { getAnswerRepository, getQuestionRepository } from '../data/repositories.js';
+import { mapToQuestionDTO, mapToQuestionId, QuestionDTO, QuestionId } from '../interfaces/question.js';
+import { Question } from '../entities/questions/question.entity.js';
+import { Answer } from '../entities/questions/answer.entity.js';
+import { mapToAnswerDTO, mapToAnswerId } from '../interfaces/answer.js';
+import { QuestionRepository } from '../data/questions/question-repository.js';
+import { LearningObjectIdentifier } from '../entities/content/learning-object-identifier.js';
+import { mapToUser } from '../interfaces/user.js';
+import { Student } from '../entities/users/student.entity.js';
+import { mapToStudent } from '../interfaces/student.js';
+
+export async function getAllQuestions(id: LearningObjectIdentifier, full: boolean): Promise<QuestionDTO[] | QuestionId[]> {
+    const questionRepository: QuestionRepository = getQuestionRepository();
+    const questions = await questionRepository.findAllQuestionsAboutLearningObject(id);
+
+    if (!questions) {
+        return [];
+    }
+
+    const questionsDTO: QuestionDTO[] = questions.map(mapToQuestionDTO);
+
+    if (full) {
+        return questionsDTO;
+    }
+
+    return questionsDTO.map(mapToQuestionId);
+}
+
+async function fetchQuestion(questionId: QuestionId): Promise<Question | null> {
+    const questionRepository = getQuestionRepository();
+
+    return await questionRepository.findOne({
+        learningObjectHruid: questionId.learningObjectIdentifier.hruid,
+        learningObjectLanguage: questionId.learningObjectIdentifier.language,
+        learningObjectVersion: questionId.learningObjectIdentifier.version,
+        sequenceNumber: questionId.sequenceNumber,
+    });
+}
+
+export async function getQuestion(questionId: QuestionId): Promise<QuestionDTO | null> {
+    const question = await fetchQuestion(questionId);
+
+    if (!question) {
+        return null;
+    }
+
+    return mapToQuestionDTO(question);
+}
+
+export async function getAnswersByQuestion(questionId: QuestionId, full: boolean) {
+    const answerRepository = getAnswerRepository();
+    const question = await fetchQuestion(questionId);
+
+    if (!question) {
+        return [];
+    }
+
+    const answers: Answer[] = await answerRepository.findAllAnswersToQuestion(question);
+
+    if (!answers) {
+        return [];
+    }
+
+    const answersDTO = answers.map(mapToAnswerDTO);
+
+    if (full) {
+        return answersDTO;
+    }
+
+    return answersDTO.map(mapToAnswerId);
+}
+
+export async function createQuestion(questionDTO: QuestionDTO) {
+    const questionRepository = getQuestionRepository();
+
+    const author = mapToStudent(questionDTO.author);
+
+    try {
+        await questionRepository.createQuestion({
+            loId: questionDTO.learningObjectIdentifier,
+            author,
+            content: questionDTO.content,
+        });
+    } catch (e) {
+        return null;
+    }
+
+    return questionDTO;
+}
+
+export async function deleteQuestion(questionId: QuestionId) {
+    const questionRepository = getQuestionRepository();
+
+    const question = await fetchQuestion(questionId);
+
+    if (!question) {
+        return null;
+    }
+
+    try {
+        await questionRepository.removeQuestionByLearningObjectAndSequenceNumber(questionId.learningObjectIdentifier, questionId.sequenceNumber);
+    } catch (e) {
+        return null;
+    }
+
+    return question;
+}
--- a/backend/src/services/students.ts
+++ b/backend/src/services/students.ts
@ -0,0 +1,126 @@
+import { getClassRepository, getGroupRepository, getStudentRepository, getSubmissionRepository } from '../data/repositories.js';
+import { Class } from '../entities/classes/class.entity.js';
+import { Student } from '../entities/users/student.entity.js';
+import { AssignmentDTO } from '../interfaces/assignment.js';
+import { ClassDTO, mapToClassDTO } from '../interfaces/class.js';
+import { GroupDTO, mapToGroupDTO, mapToGroupDTOId } from '../interfaces/group.js';
+import { mapToStudent, mapToStudentDTO, StudentDTO } from '../interfaces/student.js';
+import { mapToSubmissionDTO, SubmissionDTO } from '../interfaces/submission.js';
+import { getAllAssignments } from './assignments.js';
+import { UserService } from './users.js';
+
+export async function getAllStudents(): Promise<StudentDTO[]> {
+    const studentRepository = getStudentRepository();
+    const users = await studentRepository.findAll();
+    return users.map(mapToStudentDTO);
+}
+
+export async function getAllStudentIds(): Promise<string[]> {
+    const users = await getAllStudents();
+    return users.map((user) => user.username);
+}
+
+export async function getStudent(username: string): Promise<StudentDTO | null> {
+    const studentRepository = getStudentRepository();
+    const user = await studentRepository.findByUsername(username);
+    return user ? mapToStudentDTO(user) : null;
+}
+
+export async function createStudent(userData: StudentDTO): Promise<StudentDTO | null> {
+    const studentRepository = getStudentRepository();
+
+    try {
+        const newStudent = studentRepository.create(mapToStudent(userData));
+        await studentRepository.save(newStudent);
+
+        return mapToStudentDTO(newStudent);
+    } catch (e) {
+        console.log(e);
+        return null;
+    }
+}
+
+export async function deleteStudent(username: string): Promise<StudentDTO | null> {
+    const studentRepository = getStudentRepository();
+
+    const user = await studentRepository.findByUsername(username);
+
+    if (!user) {
+        return null;
+    }
+
+    try {
+        await studentRepository.deleteByUsername(username);
+
+        return mapToStudentDTO(user);
+    } catch (e) {
+        console.log(e);
+        return null;
+    }
+}
+
+export async function getStudentClasses(username: string, full: boolean): Promise<ClassDTO[] | string[]> {
+    const studentRepository = getStudentRepository();
+    const student = await studentRepository.findByUsername(username);
+
+    if (!student) {
+        return [];
+    }
+
+    const classRepository = getClassRepository();
+    const classes = await classRepository.findByStudent(student);
+
+    if (full) {
+        return classes.map(mapToClassDTO);
+    }
+
+    return classes.map((cls) => cls.classId!);
+}
+
+export async function getStudentAssignments(username: string, full: boolean): Promise<AssignmentDTO[]> {
+    const studentRepository = getStudentRepository();
+    const student = await studentRepository.findByUsername(username);
+
+    if (!student) {
+        return [];
+    }
+
+    const classRepository = getClassRepository();
+    const classes = await classRepository.findByStudent(student);
+
+    const assignments = (await Promise.all(classes.map(async (cls) => await getAllAssignments(cls.classId!, full)))).flat();
+
+    return assignments;
+}
+
+export async function getStudentGroups(username: string, full: boolean): Promise<GroupDTO[]> {
+    const studentRepository = getStudentRepository();
+    const student = await studentRepository.findByUsername(username);
+
+    if (!student) {
+        return [];
+    }
+
+    const groupRepository = getGroupRepository();
+    const groups = await groupRepository.findAllGroupsWithStudent(student);
+
+    if (full) {
+        return groups.map(mapToGroupDTO);
+    }
+
+    return groups.map(mapToGroupDTOId);
+}
+
+export async function getStudentSubmissions(username: string): Promise<SubmissionDTO[]> {
+    const studentRepository = getStudentRepository();
+    const student = await studentRepository.findByUsername(username);
+
+    if (!student) {
+        return [];
+    }
+
+    const submissionRepository = getSubmissionRepository();
+    const submissions = await submissionRepository.findAllSubmissionsForStudent(student);
+
+    return submissions.map(mapToSubmissionDTO);
+}
--- a/backend/src/services/submissions.ts
+++ b/backend/src/services/submissions.ts
@ -0,0 +1,51 @@
+import { getGroupRepository, getSubmissionRepository } from '../data/repositories.js';
+import { Language } from '../entities/content/language.js';
+import { LearningObjectIdentifier } from '../entities/content/learning-object-identifier.js';
+import { mapToSubmission, mapToSubmissionDTO, SubmissionDTO } from '../interfaces/submission.js';
+
+export async function getSubmission(
+    learningObjectHruid: string,
+    language: Language,
+    version: number,
+    submissionNumber: number
+): Promise<SubmissionDTO | null> {
+    const loId = new LearningObjectIdentifier(learningObjectHruid, language, version);
+
+    const submissionRepository = getSubmissionRepository();
+    const submission = await submissionRepository.findSubmissionByLearningObjectAndSubmissionNumber(loId, submissionNumber);
+
+    if (!submission) {
+        return null;
+    }
+
+    return mapToSubmissionDTO(submission);
+}
+
+export async function createSubmission(submissionDTO: SubmissionDTO) {
+    const submissionRepository = getSubmissionRepository();
+    const submission = mapToSubmission(submissionDTO);
+
+    try {
+        const newSubmission = await submissionRepository.create(submission);
+        await submissionRepository.save(newSubmission);
+    } catch (e) {
+        return null;
+    }
+
+    return submission;
+}
+
+export async function deleteSubmission(learningObjectHruid: string, language: Language, version: number, submissionNumber: number) {
+    const submissionRepository = getSubmissionRepository();
+
+    const submission = getSubmission(learningObjectHruid, language, version, submissionNumber);
+
+    if (!submission) {
+        return null;
+    }
+
+    const loId = new LearningObjectIdentifier(learningObjectHruid, language, version);
+    await submissionRepository.deleteSubmissionByLearningObjectAndSubmissionNumber(loId, submissionNumber);
+
+    return submission;
+}
--- a/backend/src/services/teachers.ts
+++ b/backend/src/services/teachers.ts
@ -0,0 +1,129 @@
+import {
+    getClassRepository,
+    getLearningObjectRepository,
+    getQuestionRepository,
+    getStudentRepository,
+    getTeacherRepository,
+} from '../data/repositories.js';
+import { Teacher } from '../entities/users/teacher.entity.js';
+import { ClassDTO, mapToClassDTO } from '../interfaces/class.js';
+import { getClassStudents } from './class.js';
+import { StudentDTO } from '../interfaces/student.js';
+import { mapToQuestionDTO, mapToQuestionId, QuestionDTO, QuestionId } from '../interfaces/question.js';
+import { UserService } from './users.js';
+import { mapToUser } from '../interfaces/user.js';
+import { mapToTeacher, mapToTeacherDTO, TeacherDTO } from '../interfaces/teacher.js';
+
+export async function getAllTeachers(): Promise<TeacherDTO[]> {
+    const teacherRepository = getTeacherRepository();
+    const users = await teacherRepository.findAll();
+    return users.map(mapToTeacherDTO);
+}
+
+export async function getAllTeacherIds(): Promise<string[]> {
+    const users = await getAllTeachers();
+    return users.map((user) => user.username);
+}
+
+export async function getTeacher(username: string): Promise<TeacherDTO | null> {
+    const teacherRepository = getTeacherRepository();
+    const user = await teacherRepository.findByUsername(username);
+    return user ? mapToTeacherDTO(user) : null;
+}
+
+export async function createTeacher(userData: TeacherDTO): Promise<TeacherDTO | null> {
+    const teacherRepository = getTeacherRepository();
+
+    try {
+        const newTeacher = teacherRepository.create(mapToTeacher(userData));
+        await teacherRepository.save(newTeacher);
+
+        return mapToTeacherDTO(newTeacher);
+    } catch (e) {
+        console.log(e);
+        return null;
+    }
+}
+
+export async function deleteTeacher(username: string): Promise<TeacherDTO | null> {
+    const teacherRepository = getTeacherRepository();
+
+    const user = await teacherRepository.findByUsername(username);
+
+    if (!user) {
+        return null;
+    }
+
+    try {
+        await teacherRepository.deleteByUsername(username);
+
+        return mapToTeacherDTO(user);
+    } catch (e) {
+        console.log(e);
+        return null;
+    }
+}
+
+export async function fetchClassesByTeacher(username: string): Promise<ClassDTO[]> {
+    const teacherRepository = getTeacherRepository();
+    const teacher = await teacherRepository.findByUsername(username);
+    if (!teacher) {
+        return [];
+    }
+
+    const classRepository = getClassRepository();
+    const classes = await classRepository.findByTeacher(teacher);
+    return classes.map(mapToClassDTO);
+}
+
+export async function getClassesByTeacher(username: string): Promise<ClassDTO[]> {
+    return await fetchClassesByTeacher(username);
+}
+
+export async function getClassIdsByTeacher(username: string): Promise<string[]> {
+    const classes = await fetchClassesByTeacher(username);
+    return classes.map((cls) => cls.id);
+}
+
+export async function fetchStudentsByTeacher(username: string) {
+    const classes = await getClassIdsByTeacher(username);
+
+    return (await Promise.all(classes.map(async (id) => getClassStudents(id)))).flat();
+}
+
+export async function getStudentsByTeacher(username: string): Promise<StudentDTO[]> {
+    return await fetchStudentsByTeacher(username);
+}
+
+export async function getStudentIdsByTeacher(username: string): Promise<string[]> {
+    const students = await fetchStudentsByTeacher(username);
+    return students.map((student) => student.username);
+}
+
+export async function fetchTeacherQuestions(username: string): Promise<QuestionDTO[]> {
+    const teacherRepository = getTeacherRepository();
+    const teacher = await teacherRepository.findByUsername(username);
+    if (!teacher) {
+        throw new Error(`Teacher with username '${username}' not found.`);
+    }
+
+    // Find all learning objects that this teacher manages
+    const learningObjectRepository = getLearningObjectRepository();
+    const learningObjects = await learningObjectRepository.findAllByTeacher(teacher);
+
+    // Fetch all questions related to these learning objects
+    const questionRepository = getQuestionRepository();
+    const questions = await questionRepository.findAllByLearningObjects(learningObjects);
+
+    return questions.map(mapToQuestionDTO);
+}
+
+export async function getQuestionsByTeacher(username: string): Promise<QuestionDTO[]> {
+    return await fetchTeacherQuestions(username);
+}
+
+export async function getQuestionIdsByTeacher(username: string): Promise<QuestionId[]> {
+    const questions = await fetchTeacherQuestions(username);
+
+    return questions.map(mapToQuestionId);
+}
--- a/backend/src/services/users.ts
+++ b/backend/src/services/users.ts
@ -0,0 +1,41 @@
+import { UserRepository } from '../data/users/user-repository.js';
+import { UserDTO, mapToUser, mapToUserDTO } from '../interfaces/user.js';
+import { User } from '../entities/users/user.entity.js';
+
+export class UserService<T extends User> {
+    protected repository: UserRepository<T>;
+
+    constructor(repository: UserRepository<T>) {
+        this.repository = repository;
+    }
+
+    async getAllUsers(): Promise<UserDTO[]> {
+        const users = await this.repository.findAll();
+        return users.map(mapToUserDTO);
+    }
+
+    async getAllUserIds(): Promise<string[]> {
+        const users = await this.getAllUsers();
+        return users.map((user) => user.username);
+    }
+
+    async getUserByUsername(username: string): Promise<UserDTO | null> {
+        const user = await this.repository.findByUsername(username);
+        return user ? mapToUserDTO(user) : null;
+    }
+
+    async createUser(userData: UserDTO, UserClass: new () => T): Promise<T> {
+        const newUser = mapToUser(userData, new UserClass());
+        await this.repository.save(newUser);
+        return newUser;
+    }
+
+    async deleteUser(username: string): Promise<UserDTO | null> {
+        const user = await this.getUserByUsername(username);
+        if (!user) {
+            return null;
+        }
+        await this.repository.deleteByUsername(username);
+        return mapToUserDTO(user);
+    }
+}
--- a/backend/src/util/api-helper.ts
+++ b/backend/src/util/api-helper.ts
--- a/backend/src/util/translation-helper.ts
+++ b/backend/src/util/translation-helper.ts
--- a/backend/tests/data/assignments/submissions.test.ts
+++ b/backend/tests/data/assignments/submissions.test.ts
@ -32,7 +32,7 @@ describe('SubmissionRepository', () => {
    });

    it('should find the requested submission', async () => {
-        const id = new LearningObjectIdentifier('id03', Language.English, '1');
+        const id = new LearningObjectIdentifier('id03', Language.English, 1);
        const submission = await submissionRepository.findSubmissionByLearningObjectAndSubmissionNumber(id, 1);

        expect(submission).toBeTruthy();
@ -40,7 +40,7 @@ describe('SubmissionRepository', () => {
    });

    it('should find the most recent submission for a student', async () => {
-        const id = new LearningObjectIdentifier('id02', Language.English, '1');
+        const id = new LearningObjectIdentifier('id02', Language.English, 1);
        const student = await studentRepository.findByUsername('Noordkaap');
        const submission = await submissionRepository.findMostRecentSubmissionForStudent(id, student!);

@ -49,7 +49,7 @@ describe('SubmissionRepository', () => {
    });

    it('should find the most recent submission for a group', async () => {
-        const id = new LearningObjectIdentifier('id03', Language.English, '1');
+        const id = new LearningObjectIdentifier('id03', Language.English, 1);
        const class_ = await classRepository.findById('id01');
        const assignment = await assignmentRepository.findByClassAndId(class_!, 1);
        const group = await groupRepository.findByAssignmentAndGroupNumber(assignment!, 1);
@ -60,7 +60,7 @@ describe('SubmissionRepository', () => {
    });

    it('should not find a deleted submission', async () => {
-        const id = new LearningObjectIdentifier('id01', Language.English, '1');
+        const id = new LearningObjectIdentifier('id01', Language.English, 1);
        await submissionRepository.deleteSubmissionByLearningObjectAndSubmissionNumber(id, 1);

        const submission = await submissionRepository.findSubmissionByLearningObjectAndSubmissionNumber(id, 1);
--- a/backend/tests/data/content/attachments.test.ts
+++ b/backend/tests/data/content/attachments.test.ts
@ -17,11 +17,11 @@ describe('AttachmentRepository', () => {
    });

    it('should return the requested attachment', async () => {
-        const id = new LearningObjectIdentifier('id02', Language.English, '1');
+        const id = new LearningObjectIdentifier('id02', Language.English, 1);
        const learningObject = await learningObjectRepository.findByIdentifier(id);

        const attachment = await attachmentRepository.findByMostRecentVersionOfLearningObjectAndName(
-            learningObject!,
+            learningObject!.hruid,
            Language.English,
            'attachment01'
        );
--- a/backend/tests/data/content/learning-objects.test.ts
+++ b/backend/tests/data/content/learning-objects.test.ts
@ -13,8 +13,8 @@ describe('LearningObjectRepository', () => {
        learningObjectRepository = getLearningObjectRepository();
    });

-    const id01 = new LearningObjectIdentifier('id01', Language.English, '1');
-    const id02 = new LearningObjectIdentifier('test_id', Language.English, '1');
+    const id01 = new LearningObjectIdentifier('id01', Language.English, 1);
+    const id02 = new LearningObjectIdentifier('test_id', Language.English, 1);

    it('should return the learning object that matches identifier 1', async () => {
        const learningObject = await learningObjectRepository.findByIdentifier(id01);
--- a/backend/tests/data/questions/answers.test.ts
+++ b/backend/tests/data/questions/answers.test.ts
@ -20,7 +20,7 @@ describe('AnswerRepository', () => {
    });

    it('should find all answers to a question', async () => {
-        const id = new LearningObjectIdentifier('id05', Language.English, '1');
+        const id = new LearningObjectIdentifier('id05', Language.English, 1);
        const questions = await questionRepository.findAllQuestionsAboutLearningObject(id);

        const question = questions.filter((it) => it.sequenceNumber == 2)[0];
@ -35,7 +35,7 @@ describe('AnswerRepository', () => {

    it('should create an answer to a question', async () => {
        const teacher = await teacherRepository.findByUsername('FooFighters');
-        const id = new LearningObjectIdentifier('id05', Language.English, '1');
+        const id = new LearningObjectIdentifier('id05', Language.English, 1);
        const questions = await questionRepository.findAllQuestionsAboutLearningObject(id);

        const question = questions[0];
@ -54,7 +54,7 @@ describe('AnswerRepository', () => {
    });

    it('should not find a removed answer', async () => {
-        const id = new LearningObjectIdentifier('id04', Language.English, '1');
+        const id = new LearningObjectIdentifier('id04', Language.English, 1);
        const questions = await questionRepository.findAllQuestionsAboutLearningObject(id);

        await answerRepository.removeAnswerByQuestionAndSequenceNumber(questions[0], 1);
--- a/backend/tests/data/questions/questions.test.ts
+++ b/backend/tests/data/questions/questions.test.ts
@ -20,7 +20,7 @@ describe('QuestionRepository', () => {
    });

    it('should return all questions part of the given learning object', async () => {
-        const id = new LearningObjectIdentifier('id05', Language.English, '1');
+        const id = new LearningObjectIdentifier('id05', Language.English, 1);
        const questions = await questionRepository.findAllQuestionsAboutLearningObject(id);

        expect(questions).toBeTruthy();
@ -28,7 +28,7 @@ describe('QuestionRepository', () => {
    });

    it('should create new question', async () => {
-        const id = new LearningObjectIdentifier('id03', Language.English, '1');
+        const id = new LearningObjectIdentifier('id03', Language.English, 1);
        const student = await studentRepository.findByUsername('Noordkaap');
        await questionRepository.createQuestion({
            loId: id,
@ -42,7 +42,7 @@ describe('QuestionRepository', () => {
    });

    it('should not find removed question', async () => {
-        const id = new LearningObjectIdentifier('id04', Language.English, '1');
+        const id = new LearningObjectIdentifier('id04', Language.English, 1);
        await questionRepository.removeQuestionByLearningObjectAndSequenceNumber(id, 1);

        const question = await questionRepository.findAllQuestionsAboutLearningObject(id);
--- a/backend/tests/test_assets/assignments/submission.testdata.ts
+++ b/backend/tests/test_assets/assignments/submission.testdata.ts
@ -12,7 +12,7 @@ export function makeTestSubmissions(
    const submission01 = em.create(Submission, {
        learningObjectHruid: 'id03',
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        submissionNumber: 1,
        submitter: students[0],
        submissionTime: new Date(2025, 2, 20),
@ -23,7 +23,7 @@ export function makeTestSubmissions(
    const submission02 = em.create(Submission, {
        learningObjectHruid: 'id03',
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        submissionNumber: 2,
        submitter: students[0],
        submissionTime: new Date(2025, 2, 25),
@ -34,7 +34,7 @@ export function makeTestSubmissions(
    const submission03 = em.create(Submission, {
        learningObjectHruid: 'id02',
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        submissionNumber: 1,
        submitter: students[0],
        submissionTime: new Date(2025, 2, 20),
@ -44,7 +44,7 @@ export function makeTestSubmissions(
    const submission04 = em.create(Submission, {
        learningObjectHruid: 'id02',
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        submissionNumber: 2,
        submitter: students[0],
        submissionTime: new Date(2025, 2, 25),
@ -54,7 +54,7 @@ export function makeTestSubmissions(
    const submission05 = em.create(Submission, {
        learningObjectHruid: 'id01',
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        submissionNumber: 1,
        submitter: students[1],
        submissionTime: new Date(2025, 2, 20),
--- a/backend/tests/test_assets/content/learning-paths.testdata.ts
+++ b/backend/tests/test_assets/content/learning-paths.testdata.ts
@ -77,7 +77,7 @@ export function makeTestLearningPaths(em: EntityManager<IDatabaseDriver<Connecti
        admins: [],
        title: 'repertoire Tool',
        description: 'all about Tool',
-        image: '',
+        image: null,
        nodes: nodes01,
    });

@ -92,7 +92,7 @@ export function makeTestLearningPaths(em: EntityManager<IDatabaseDriver<Connecti
        admins: [],
        title: 'repertoire Dire Straits',
        description: 'all about Dire Straits',
-        image: '',
+        image: null,
        nodes: nodes02,
    });

--- a/backend/tests/test_assets/questions/questions.testdata.ts
+++ b/backend/tests/test_assets/questions/questions.testdata.ts
@ -6,7 +6,7 @@ import { Student } from '../../../src/entities/users/student.entity';
 export function makeTestQuestions(em: EntityManager<IDatabaseDriver<Connection>>, students: Array<Student>): Array<Question> {
    const question01 = em.create(Question, {
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        learningObjectHruid: 'id05',
        sequenceNumber: 1,
        author: students[0],
@ -16,7 +16,7 @@ export function makeTestQuestions(em: EntityManager<IDatabaseDriver<Connection>>

    const question02 = em.create(Question, {
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        learningObjectHruid: 'id05',
        sequenceNumber: 2,
        author: students[2],
@ -26,7 +26,7 @@ export function makeTestQuestions(em: EntityManager<IDatabaseDriver<Connection>>

    const question03 = em.create(Question, {
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        learningObjectHruid: 'id04',
        sequenceNumber: 1,
        author: students[0],
@ -36,7 +36,7 @@ export function makeTestQuestions(em: EntityManager<IDatabaseDriver<Connection>>

    const question04 = em.create(Question, {
        learningObjectLanguage: Language.English,
-        learningObjectVersion: '1',
+        learningObjectVersion: 1,
        learningObjectHruid: 'id01',
        sequenceNumber: 1,
        author: students[1],
--- a/package-lock.json
+++ b/package-lock.json