500 Error when using method populate in Express and Mongo - node.js

Question

I cannot fetch users data from Mongo when I use populate() method for posts of users.
router.get("/users", (req, res) => {
User.find()
.populate("posts")
.exec()
.then((users) => {
res.json({ users });
})
.catch((err) => console.log(err));
});
Mongo Schema
const mongoose = require("mongoose");
const Schema = mongoose.Schema;
const { ObjectId } = mongoose.Schema.Types;
const Post = require("../models/Post");
const UserSchema = new Schema({
name: {
type: String,
required: true
},
username: {
type: String,
requied: true
},
userimg: {
type: String
},
followers: [
{
type: ObjectId,
ref: "User"
}
],
following: [
{
type: ObjectId,
ref: "User"
}
],
posts: [
{
type: ObjectId,
ref: "Post"
}
],
email: {
type: String,
required: true
},
password: {
type: String,
required: true
},
date: {
type: Date,
default: Date.now
}
});
module.exports = User = mongoose.model("users", UserSchema);
When I remove .populate("posts") than I get 200 Success status and users data but without popoulation of referred posts from the posts collection.

Answer 1

So i'll be doing a little modification to your model file
const mongoose = require("mongoose");
const Schema = mongoose.Schema;
const Post = require("../models/Post");
const UserSchema = new Schema({
name: {
type: String,
required: true
},
username: {
type: String,
requied: true
},
userimg: {
type: String
},
followers: [
{
type: Schema.Types.ObjectId,
ref: "User"
}
],
following: [
{
type: Schema.Types.ObjectId,
ref: "User"
}
],
posts: [
{
type: Schema.Types.ObjectId,
ref: "Post"
}
],
email: {
type: String,
required: true
},
password: {
type: String,
required: true
},
date: {
type: Date,
default: Date.now
}
});
module.exports = User = mongoose.model("User", UserSchema);
Can you change your exec() to execPopulate()
router.get("/users", (req, res) => {
User.find()
.populate("posts")
.execPopulate()
.then((users) => {
res.json({ users });
})
.catch((err) => console.log(err));
});

Answer 2

Thank you all for your help. I found the error:
ref: "posts" instead of ref: "Post"
ref: "users" instead of ref: "User"