Merge branch 'feat/service-layer' into feat/service-layer-adriaan

# Conflicts:
#	backend/src/controllers/classes.ts
#	backend/src/controllers/students.ts
#	backend/src/data/users/teacher-repository.ts
#	backend/src/interfaces/assignment.ts
#	backend/src/interfaces/teacher.ts
#	backend/src/routes/classes.ts
#	backend/src/services/assignments.ts
#	backend/src/services/class.ts
#	backend/src/services/students.ts
#	backend/src/util/translation-helper.ts

backend/src/interfaces/question.ts

@@ -0,0 +1,41 @@
+import {Question} from "../entities/questions/question.entity";
+import {Enum, PrimaryKey} from "@mikro-orm/core";
+import {Language} from "../entities/content/language";
+
+export interface QuestionDTO {
+    learningObjectHruid: string;
+    learningObjectLanguage: string;
+    learningObjectVersion: string;
+    sequenceNumber: number;
+    authorUsername: string;
+    timestamp: string;
+    content: string;
+    endpoints?: {
+        classes: string;
+        questions: string;
+        invitations: string;
+        groups: string;
+    };
+}
+
+/**
+ * Convert a Question entity to a DTO format.
+ */
+export function mapToQuestionDTO(question: Question): QuestionDTO {
+    return {
+        learningObjectHruid: question.learningObjectHruid,
+        learningObjectLanguage: question.learningObjectLanguage,
+        learningObjectVersion: question.learningObjectVersion,
+        sequenceNumber: question.sequenceNumber,
+        authorUsername: question.author.username,
+        timestamp: question.timestamp.toISOString(),
+        content: question.content,
+    };
+}
+
+export interface QuestionId {
+    learningObjectHruid: string,
+    learningObjectLanguage: Language,
+    learningObjectVersion: string,
+    sequenceNumber: number
+}

backend/src/interfaces/teacher.ts

@@ -1,23 +1,36 @@
 import { Teacher } from "../entities/users/teacher.entity.js";
 
+/**
+ * Teacher Data Transfer Object
+ */
 export interface TeacherDTO {
-    id: string;
     username: string;
     firstName: string;
     lastName: string;
     endpoints?: {
+        self: string;
         classes: string;
         questions: string;
         invitations: string;
-        groups: string;
     };
 }
 
+/**
+ * Maps a Teacher entity to a TeacherDTO
+ */
 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();
+    teacher.username = teacherData.username;
+    teacher.firstName = teacherData.firstName;
+    teacher.lastName = teacherData.lastName;
+
+    return teacher;
+}