Cannot overwrite model once compiled Mongoose

Question

Not Sure what I'm doing wrong, here is my check.js

var db = mongoose.createConnection('localhost', 'event-db');
db.on('error', console.error.bind(console, 'connection error:'));

var a1= db.once('open',function(){
var user = mongoose.model('users',{ 
       name:String,
       email:String,
       password:String,
       phone:Number,
      _enabled:Boolean
     });

user.find({},{},function (err, users) {
    mongoose.connection.close();
    console.log("Username supplied"+username);
    //doSomethingHere })
    });

and here is my insert.js

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/event-db')

var user = mongoose.model('users',{
     name:String,
     email:String,
     password: String,
     phone:Number,
     _enabled:Boolean
   });

var new_user = new user({
     name:req.body.name,
     email: req.body.email,
     password: req.body.password,
     phone: req.body.phone,
     _enabled:false
   });

new_user.save(function(err){
    if(err) console.log(err); 
   });

Whenever I'm trying to run check.js, I'm getting this error

Cannot overwrite 'users' model once compiled.

I understand that this error comes due to mismatching of Schema, but I cannot see where this is happening ? I'm pretty new to mongoose and nodeJS.

Here is what I'm getting from the client interface of my MongoDB:

MongoDB shell version: 2.4.6 connecting to: test 
> use event-db 
  switched to db event-db 
> db.users.find() 
  { "_id" : ObjectId("52457d8718f83293205aaa95"), 
    "name" : "MyName", 
    "email" : "[email protected]", 
    "password" : "myPassword", 
    "phone" : 900001123, 
    "_enable" : true 
  } 
>

Answer 1

Another reason you might get this error is if you use the same model in different files but your require path has a different case.

For example, in my situation I had require('./models/User') in one file, and then in another file where I needed access to the User model, I had require('./models/user').

I guess the lookup for modules & mongoose is treating it as a different file. Once I made sure the case matched in both it was no longer an issue.

Answer 2

The error is occurring because you already have a schema defined, and then you are defining the schema again. Generally what you should do is instantiate the schema once, and then have a global object call it when it needs it.

For example:

user_model.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var userSchema = new Schema({
   name:String,
   email:String,
   password:String,
   phone:Number,
   _enabled:Boolean
});
module.exports = mongoose.model('users', userSchema);          

check.js

var mongoose = require('mongoose');
var User = require('./user_model.js');

var db = mongoose.createConnection('localhost', 'event-db');
db.on('error', console.error.bind(console, 'connection error:'));
var a1= db.once('open',function(){
  User.find({},{},function (err, users) {
    mongoose.connection.close();
    console.log("Username supplied"+username);
    //doSomethingHere 
  })
});

insert.js

var mongoose = require('mongoose');
var User = require('./user_model.js');

mongoose.connect('mongodb://localhost/event-db');
var new_user = new User({
    name:req.body.name
  , email: req.body.email
  , password: req.body.password
  , phone: req.body.phone
  , _enabled:false 
});
new_user.save(function(err){
  if(err) console.log(err); 
});

Answer 3

I had this issue while 'watching' tests. When the tests were edited, the watch re-ran the tests, but they failed due to this very reason.

I fixed it by checking if the model exists then use it, else create it.

import mongoose from 'mongoose';
import user from './schemas/user';

export const User = mongoose.models.User || mongoose.model('User', user);

Answer 4

I had this issue while unit testing.

The first time you call the model creation function, mongoose stores the model under the key you provide (e.g. 'users'). If you call the model creation function with the same key more than once, mongoose won't let you overwrite the existing model.

You can check if the model already exists in mongoose with:

let users = mongoose.model('users')

This will throw an error if the model does not exist, so you can wrap it in a try/catch in order to either get the model, or create it:

let users
try {
  users = mongoose.model('users')
} catch (error) {
  users = mongoose.model('users', <UsersSchema...>)
}

Answer 5

If you are using Serverless offline and don't want to use --skipCacheInvalidation, you can very well use:

module.exports = mongoose.models.Users || mongoose.model('Users', UsersSchema);

Answer 6

I have been experiencing this issue & it was not because of the schema definitions but rather of serverless offline mode - I just managed to resolve it with this:

serverless offline --skipCacheInvalidation

Which is mentioned here https://github.com/dherault/serverless-offline/issues/258

Hopefully that helps someone else who is building their project on serverless and running offline mode.

Answer 7

If you made it here it is possible that you had the same problem i did. My issue was that i was defining another model with the same name. I called my gallery and my file model "File". Darn you copy and paste!

Answer 8

I solved this by adding

mongoose.models = {}

before the line :

mongoose.model(<MODEL_NAME>, <MODEL_SCHEMA>)

Hope it solves your problem

Answer 9

Click here! Official example. Most important! thing is to export like this

export default mongoose.models.Item || mongoose.model('Item', itemsSchema)

Answer 10

This happened to me when I write like this:

import User from '../myuser/User.js';

However, the true path is '../myUser/User.js'

Answer 11

To Solve this check if the model exists before to do the creation:

if (!mongoose.models[entityDBName]) {
  return mongoose.model(entityDBName, entitySchema);
}
else {
  return mongoose.models[entityDBName];
}

Answer 12

Here is one more reason why this can happen. Perhaps this can help someone else. Notice the difference, Members vs Member. They must be the same...

export default mongoose.models.Members || mongoose.model('Member', FamilySchema)

Change to:

export default mongoose.models.Member || mongoose.model('Member', FamilySchema)

Answer 13

I know there is an accepted solution but I feel that the current solution results in a lot of boilerplate just so that you can test Models. My solution is essentially to take you model and place it inside of a function resulting in returning the new Model if the Model has not been registered but returning the existing Model if it has.

function getDemo () {
  // Create your Schema
  const DemoSchema = new mongoose.Schema({
    name: String,
    email: String
  }, {
    collection: 'demo'
  })
  // Check to see if the model has been registered with mongoose
  // if it exists return that model
  if (mongoose.models && mongoose.models.Demo) return mongoose.models.Demo
  // if no current model exists register and return new model
  return mongoose.model('Demo', DemoSchema)
}

export const Demo = getDemo()

Opening and closing connections all over the place is frustrating and does not compress well.

This way if I were to require the model two different places or more specifically in my tests I would not get errors and all the correct information is being returned.

Answer 14

This may give a hit for some, but I got the error as well and realized that I just misspelled the user model on importing.

wrong: const User = require('./UserModel'); correct: const User = require('./userModel');

Unbelievable but consider it.

Answer 15

What you can also do is at your export, make sure to export an existing instance if one exists.

Typescript solution:

import { Schema, Document, model, models } from 'mongoose';

const UserSchema: Schema = new Schema({
    name: {
        type: String
    }
});

export interface IUser extends Document {
    name: string
}

export default models.Users || model<IUser>('Users', UserSchema);

Answer 16

I faced this issue using Next.js and TypeScript. The top answers made it such that typings would not work.

This is what works for me:

const { Schema } = mongoose

export interface IUser {
  name: string
  email: string
}

const UserSchema = new Schema<IUser>({
  name: { type: String, required: true },
  email: { type: String, required: true },
})

const UserModel = () => mongoose.model<IUser>('User', UserSchema)

export default (mongoose.models.User || UserModel()) as ReturnType<
  typeof UserModel
>

Answer 17

This problem might occur if you define 2 different schema's with same Collection name

Answer 18

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const userSchema = new Schema({
    name: String,
});

// Trying to get the existing model to avoid OverwriteModelError
module.exports = mongoose.model("user") || mongoose.model('user', userSchema);

Answer 19

You can easily solve this by doing

delete mongoose.connection.models['users'];
const usersSchema = mongoose.Schema({...});
export default mongoose.model('users', usersSchema);

Answer 20

There is another way to throw this error.

Keep in mind that the path to the model is case sensitive.

In this similar example involving the "Category" model, the error was thrown under these conditions:

1) The require statement was mentioned in two files: ..category.js and ..index.js 2) I the first, the case was correct, in the second file it was not as follows:

category.js

index.js

Answer 21

I solved this issue by doing this

// Created Schema - Users
// models/Users.js
const mongoose = require("mongoose");

const Schema = mongoose.Schema;

export const userSchema = new Schema({
  // ...
});

Then in other files

// Another file
// index.js
import { userSchema } from "../models/Users";
const conn = mongoose.createConnection(process.env.CONNECTION_STRING, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
});
conn.models = {};
const Users = conn.model("Users", userSchema);
const results = await Users.find({});

Better Solution

let User;
try {
  User = mongoose.model("User");
} catch {
  User = mongoose.model("User", userSchema);
}

I hope this helps...

Answer 22

I faced the same Issue with NextJS and MongoDB atlas. I had a models folder with the model of session stored, but the problem was not that I defined the Schema twice.

1. Make sure the Collection is empty and does not have a previous Document
2. If it does, then Simply declare a Model without Schema, like this:

const Session = mongoose.model("user_session_collection")

3. You can delete the previous records or backup them, create the schema and then apply query on the database.

Hope it helped

Answer 23

Below is the full solution to similar problem when using Mongoose with Pagination in combination with Nuxt and Typescript:

import {model, models, Schema, PaginateModel, Document } from 'mongoose';

import { default as mongoosePaginate } from 'mongoose-paginate-v2';

export interface IUser extends Document {
    name: string;
}

const UserSchema: Schema = new Schema({
    name: String
});

UserSchema.plugin(mongoosePaginate)

interface User<T extends Document> extends PaginateModel<T> {}


const User: User<IUser> = models['User'] as User<IUser> || model<IUser>('User', UserSchema) as User<IUser>;

export default User

---

tsconfig.json:

{
    "compilerOptions": {
        "target": "ES2018",
        "module": "ESNext",
        "moduleResolution": "Node",
        "lib": ["ESNext", "ESNext.AsyncIterable", "DOM"],
        "esModuleInterop": true,
        "allowJs": true,
        "sourceMap": true,
        "strict": true,
        "noEmit": true,
        "baseUrl": ".",
        "paths": {
            "~/*": ["./*"],
            "@/*": ["./*"]
        },
        "types": ["@types/node", "@nuxt/types"]
    },
    "exclude": ["node_modules"]
}

To make pagination working you will also need to install @types/mongoose-paginate-v2

---

The above solution should also deal with problems related to hot reloading with Nuxt (ServerMiddleware errors) and pagination plugin registration.

Answer 24

A solution that worked for me was just to check if an instance of the model exists before creating and exporting the model.

import mongoose from "mongoose";
const { Schema } = mongoose;
const mongoosePaginate = require("mongoose-paginate");

const articleSchema = new Schema({
  title: String, // String is shorthand for {type: String}
  summary: String,
  data: String,
  comments: [{ body: String, date: Date }],
  date: { type: Date, default: Date.now },
  published: { type: Boolean, default: true },
  tags: [{ name: String }],
  category: String,
  _id: String,
});


const Post = mongoose.models.Post ? mongoose.models.Post : mongoose.model("Post",articleSchema);

export default Post;

Answer 25

If you have overWrite problem. You should make check the models.

let User

if (mongoose.models.User) {
    User = mongoose.model('User')
} else {
    User = mongoose.model('User', userSchema)
}

Answer 26

I have the same issue but when i check my code then I figure out that there is a typo in code

Error Code 👇

import mongoose from "mongoose";

const contentSchema = new mongoose.Schema({
    content: {
        type: String,
        required: true
    },
}, { timestamps: true })

const ContentPost = mongoose.Schema.contents || mongoose.model("contents", contentSchema);

export default ContentPost;

Error Free Code 👇

import mongoose from "mongoose";

const contentSchema = new mongoose.Schema({
    content: {
        type: String,
        required: true
    },
}, { timestamps: true })

const ContentPost = mongoose.models.contents || mongoose.model("contents", contentSchema);

export default ContentPost;

I write the Schema in place of of model const ContentPost = mongoose.Schema.contents || mongoose.model("contents", contentSchema);

Answer 27

The schema definition should be unique for a collection, it should not be more then one schema for a collection.

Answer 28

If you want to overwrite the existing class for different collection using typescript
then you have to inherit the existing class from different class.

export class User extends Typegoose{
  @prop
  username?:string
  password?:string
}


export class newUser extends User{
    constructor() {
        super();
    }
}

export const UserModel = new User ().getModelForClass(User , { schemaOptions: { collection: "collection1" } });

export const newUserModel = new newUser ().getModelForClass(newUser , { schemaOptions: { collection: "collection2" } });

Answer 29

I had the same problem, reason was I defined schema an model in a JS function, they should be defined globally in a node module, not in a function.

Answer 30

just export like this exports.User = mongoose.models.User || mongoose.model('User', userSchema);