fix(backend): Fouten in entity-definities gecorrigeerd.

backend/src/entities/users/student.entity.ts

@@ -1,9 +1,13 @@
 import {User} from "./user.entity";
 import {Collection, Entity, ManyToMany} from '@mikro-orm/core';
 import {Class} from "../classes/class.entity";
+import {Group} from "../assigments/group.entity";
 
 @Entity()
 export class Student extends User {
     @ManyToMany(() => Class)
     classes!: Collection<Class>;
+
+    @ManyToMany(() => Group)
+    groups!: Collection<Group>;
 }