diff --git a/src/models/ActivityModel.ts b/src/models/ActivityModel.ts
index a97b167..8c50f5c 100644
--- a/src/models/ActivityModel.ts
+++ b/src/models/ActivityModel.ts
@@ -2,10 +2,10 @@ import { Schema, Types, model } from 'mongoose';
 
 export interface IActivity {
 	id: string;
+	owner: Types.ObjectId;
+	classroom: Types.ObjectId;
 	title: string;
 	description: string;
-	classroomId: string;
-	owner: Types.ObjectId;
 	dueDate?: string;
 	createdAt: string;
 	type: 'assignment' | 'material';
@@ -46,6 +46,12 @@ const activitySchema = new Schema<IActivity>(
 			required: true,
 			index: true
 		},
+		classroom: {
+			type: Schema.Types.ObjectId,
+			ref: 'classroom',
+			required: true,
+			index: true
+		},
 		title: {
 			type: String,
 			required: true
@@ -54,10 +60,6 @@ const activitySchema = new Schema<IActivity>(
 			type: String,
 			required: true
 		},
-		classroomId: {
-			type: String,
-			required: true
-		},
 		dueDate: {
 			type: String,
 			required: false
diff --git a/src/routes/classroom/activities/index.ts b/src/routes/classroom/activities/index.ts
index 3444b43..051b42d 100644
--- a/src/routes/classroom/activities/index.ts
+++ b/src/routes/classroom/activities/index.ts
@@ -20,7 +20,7 @@ export const classroomActivitiesRoute = new Elysia({
 			if (!user) return status(400, 'Bad Request');
 			if (!user.classroomIds?.some((cId) => cId.toString() === classroomId)) return status(403, 'Forbidden');
 
-			const activities = await ActivityModel.find({ classroomId: classroomId }, { __v: 0 })
+			const activities = await ActivityModel.find({ classroom: classroomId }, { __v: 0 })
 				.lean()
 				.exec()
 				.catch(() => null);
@@ -66,7 +66,7 @@ export const classroomActivitiesRoute = new Elysia({
 			const activity = new ActivityModel({
 				title,
 				description,
-				classroomId: classroomId,
+				classroom: classroomId,
 				type,
 				content,
 				dueDate,
@@ -124,7 +124,7 @@ export const classroomActivitiesRoute = new Elysia({
 			const activity = await ActivityModel.findOne(
 				{
 					_id: activityId,
-					classroomId
+					classroom: classroomId
 				},
 				{ __v: 0 }
 			)
@@ -163,7 +163,7 @@ export const classroomActivitiesRoute = new Elysia({
 			const activity = await ActivityModel.findOne(
 				{
 					_id: activityId,
-					classroomId
+					classroom: classroomId
 				},
 				{ __v: 0 }
 			)