feat(backend): Entities toegevoegd

Entites Class, Class Join Request, Class Invitation, Assignment, Group en entities om de Dwengo-leerinhoud te modelleren, toegevoegd.

backend/src/entities/classes/class-invitation.entity.ts

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+import {Entity, ManyToOne} from "@mikro-orm/core";
+import {Teacher} from "../users/teacher.entity";
+import {Class} from "./class.entity";
+
+/**
+ * Invitation of a teacher into a class (in order to teach it).
+ */
+@Entity()
+export class TeacherInvitation {
+    @ManyToOne({entity: () => Teacher, primary: true})
+    sender!: Teacher;
+
+    @ManyToOne({entity: () => Teacher, primary: true})
+    receiver!: Teacher;
+
+    @ManyToOne({entity: () => Class, primary: true})
+    class!: Class;
+}

backend/src/entities/classes/class-join-request.entity.ts

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+import {Entity, Enum, ManyToOne} from "@mikro-orm/core";
+import {Student} from "../users/student.entity";
+import {Class} from "./class.entity";
+
+@Entity()
+export class ClassJoinRequest {
+    @ManyToOne({entity: () => Student, primary: true})
+    requester!: Student;
+
+    @ManyToOne({entity: () => Class, primary: true})
+    class!: Class;
+
+    @Enum(() => ClassJoinRequestStatus)
+    status!: ClassJoinRequestStatus;
+}
+
+export enum ClassJoinRequestStatus {
+    Open = "open",
+    Accepted = "accepted",
+    Declined = "declined"
+}

backend/src/entities/classes/class.entity.ts

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+import {Collection, Entity, ManyToMany, PrimaryKey, Property} from "@mikro-orm/core";
+import { v4 } from 'uuid';
+import {Teacher} from "../users/teacher.entity";
+import {Student} from "../users/student.entity";
+
+@Entity()
+export class Class {
+    @PrimaryKey()
+    classId = v4();
+
+    @Property({type: "string"})
+    displayName!: string;
+
+    @ManyToMany(() => Teacher)
+    teachers!: Collection<Teacher>;
+
+    @ManyToMany(() => Student)
+    students!: Collection<Student>;
+}