some changes

backend/src/interfaces/IPost.ts

-import { Document, ObjectId } from "mongoose";
+import {Document, ObjectId} from 'mongoose';
 
 export default interface IPost extends Document {
-    _id: ObjectId
-    title: string
-    description: string
-    image: File | undefined | string
-    datetime: Date
+	_id: ObjectId;
+	title: string;
+	description: string;
+	image: File | undefined | string;
+	datetime: Date;
+	user: ObjectId;
 }

backend/src/models/Post.ts

-import mongoose, { Schema } from "mongoose";
-import IPost from "../interfaces/IPost";
+import mongoose, {Schema} from 'mongoose';
+import IPost from '../interfaces/IPost';
 
-const PostsSchema: Schema = new Schema<IPost>({
+const PostsSchema: Schema = new Schema<IPost>(
+	{
 		title: {
 			type: String,
-        required: true
+			required: true,
 		},
 		description: {
 			type: String,
-        required: false
 		},
-    image: String,
+		image: {
+			type: String,
+		},
 		datetime: {
 			type: Date,
-        default: Date.now()
+			default: Date.now,
+			required: true,
+		},
+		user: {
+			type: Schema.Types.ObjectId,
+			required: true,
+		},
+	},
+	{
+		versionKey: false,
 	}
-}, {
-    versionKey: false
-})
+);
 
-export const Post = mongoose.model<IPost>('Post', PostsSchema)
+export const Post = mongoose.model<IPost>('Post', PostsSchema);
\ No newline at end of file