fix(backend): Foute entity-structuur van leerpaden verbeterd.

Ook testen geschreven voor LearningPathRepository en LearningObjectRepository.

backend/src/entities/content/learning-path-node.entity.ts

@@ -0,0 +1,37 @@
+import {Entity, Enum, ManyToOne, OneToMany, PrimaryKey, Property} from "@mikro-orm/core";
+import {Language} from "./language";
+import {LearningPath} from "./learning-path.entity";
+import {LearningPathTransition} from "./learning-path-transition.entity";
+
+@Entity()
+export class LearningPathNode {
+    @ManyToOne({ entity: () => LearningPath, primary: true })
+    learningPath!: LearningPath;
+
+    @PrimaryKey({ type: "numeric", autoincrement: true })
+    nodeNumber!: number;
+
+    @Property({ type: 'string' })
+    learningObjectHruid!: string;
+
+    @Enum({ items: () => Language })
+    language!: Language;
+
+    @Property({ type: 'number' })
+    version!: number;
+
+    @Property({ type: 'text', nullable: true })
+    instruction?: string;
+
+    @Property({ type: 'bool' })
+    startNode!: boolean;
+
+    @OneToMany({ entity: () => LearningPathTransition, mappedBy: "node" })
+    transitions: LearningPathTransition[] = [];
+
+    @Property({ length: 3 })
+    createdAt: Date = new Date();
+
+    @Property({ length: 3, onUpdate: () => new Date() })
+    updatedAt: Date = new Date();
+}