feat: gestart met implementeren van assignment service en controller laag

backend/src/services/assignments.ts

@@ -0,0 +1,20 @@
+import { getAssignmentRepository, getClassRepository } from "../data/repositories";
+import { AssignmentDTO, mapToAssignmentDTO } from "../interfaces/assignments";
+
+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, cls);
+}