"MaxListenersExceededWarning: Possible EventEmitter memory leak detected" when creating models with autoCreate: true before mongoose.connect()

[Janoyan]

Do you want to request a feature or report a bug?
Bug report

What is the current behavior?
When creating more than 10 models MaxListenersExceededWarning appears

If the current behavior is a bug, please provide the steps to reproduce.
Create more than 10 models like this:

mongoose.model<DocumentType, ModelType>(name, schema);

If you are using TypeScript, please include your tsconfig.json

{
  "compilerOptions": {
    "target": "es5"  ,
    "module": "commonjs"  ,
    "declaration": true  ,
    "declarationMap": true  ,
    "sourceMap": true  ,
    "outDir": "./dist"  ,
    "strict": true  ,
    "baseUrl": "./",
    "paths": {
      "@sm-errors": [
        "./common-library/errors"
      ],
      "@sm-microsoft-graph-api": [
        "./common-library/microsoft-graph-api"
      ],
      "@sm-shared-models": [
        "./common-library/shared-models"
      ],
      "@sm-shared-services": [
        "./common-library/shared-services"
      ],
      "@sm-lib": [
        "./common-library/lib"
      ]
    },
    "esModuleInterop": true  ,
    "skipLibCheck": true  ,
    "forceConsistentCasingInFileNames": true
  },
  "exclude": [
    "node_modules",
    "dist"
  ]
}

What is the expected behavior?
Should create more models without warnings

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

mongoose: "^5.9.27",
Node 12
MongoDB 4.2.2

Currently I solved the issue by calling the following function each time before creating models:

mongoose.connection.setMaxListeners(MAX_LISTENERS_COUNT);

but I think there should be another solution for this.

[deser]

It also happens when I use autoCreate: true on Schemas. Without that option it is ok

[deser]

Will someone look at this?

[IslandRhythms]

import { model, Schema, Model, Document, connect } from 'mongoose';

interface IUser extends Document {
  email: string;
  firstName: string;
  lastName: string;
}

const UserSchema: Schema = new Schema({
  email: { type: String, required: true },
  firstName: { type: String, required: true },
  lastName: { type: String, required: true }
});

const User: Model<IUser> = model('User', UserSchema);
const test: Model<IUser> = model('test', UserSchema);
const test1: Model<IUser> = model('test1', UserSchema);
const test2: Model<IUser> = model('test2', UserSchema);
const test3: Model<IUser> = model('test3', UserSchema);
const test4: Model<IUser> = model('test4', UserSchema);
const test5: Model<IUser> = model('test5', UserSchema);
const test6: Model<IUser> = model('test6', UserSchema);
const test7: Model<IUser> = model('test7', UserSchema);
const test8: Model<IUser> = model('test8', UserSchema);
const test9: Model<IUser> = model('test9', UserSchema);
(async function() {
  await connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true
  });

  const user: IUser = await User.create({
    email: 'bill@microsoft.com',
    firstName: 'Bill',
    lastName: 'Gates'
  });

  console.log('Done', user.email);
})();

[Janoyan]

@IslandRhythms @vkarpov15 just add autoCreate: true option to UserSchema and the warning will appear.

[IslandRhythms]

const mongoose = require('mongoose');

const UserSchema = mongoose.Schema({
  email: { type: String, required: true },
  firstName: { type: String, required: true },
  lastName: { type: String, required: true }
}, {autoCreate: true});

const User = mongoose.model('User', UserSchema);
const test = mongoose.model('test', UserSchema);
const test1 = mongoose.model('test1', UserSchema);
const test2 = mongoose.model('test2', UserSchema);
const test3 = mongoose.model('test3', UserSchema);
const test4 = mongoose.model('test4', UserSchema);
const test5 = mongoose.model('test5', UserSchema);
const test6 = mongoose.model('test6', UserSchema);
const test7 = mongoose.model('test7', UserSchema);
const test8 = mongoose.model('test8', UserSchema);
const test9 = mongoose.model('test9', UserSchema);

(async function() {
  await mongoose.connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true
  });

  const user = await User.create({
    email: 'bill@microsoft.com',
    firstName: 'Bill',
    lastName: 'Gates'
  });

  console.log('Done', user.email);
})();

[IslandRhythms]

This problem does not exist on the most recent version of mongoose.

[IslandRhythms]

@vkarpov15 its very finicky but I can reproduce it but I'm not sure what triggers it.