Mongoose 6.2.3 breaks behaviour used since 5.12.2

[SK-FComputer]

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

What is the current behavior?

If the current behavior is a bug, please provide the steps to reproduce.
After updating to typegoose 9.7.0 and mongoose 6.2.3 (Works fine in 9.6.0 and 6.2.0) i get the error:

Error [MongoNotConnectedError]: MongoClient must be connected to perform this operation
    at getTopology (D:\project\node_modules\mongoose\node_modules\mongodb\src\utils.ts:451:9)
    at Db.createCollection (D:\project\node_modules\mongoose\node_modules\mongodb\src\db.ts:261:18)
    at NativeConnection.createCollection (D:\project\node_modules\mongoose\lib\connection.js:404:11)
    at NativeConnection.Connection.onOpen (D:\project\node_modules\mongoose\lib\connection.js:635:10)
    at NativeConnection.wireup (D:\project\node_modules\mongoose\lib\drivers\node-mongodb-native\connection.js:105:13)
    at Object.onceWrapper (events.js:519:28)
    at NativeConnection.emit (events.js:400:28)
    at NativeConnection.emit (domain.js:470:12)
    at NativeConnection.set (D:\project\node_modules\mongoose\lib\connection.js:126:12)
    at NativeConnection.set (D:\project\node_modules\mongoose\lib\connection.js:119:23)

I have a master process that starts workers with the library https://threads.js.org/.
Before updating i had to create a new connection (DB class) In the child worker, such that i could use the typegoose model functions.

Code Example

DB (other DB connections here too, but truncated for example):

import { connect } from 'mongoose';
import { config } from './config';


export default class DB {
	constructor(public entities: any[] = []) {
		config;
	}

	async init(
		createMongoDB: boolean = true,
		debug: boolean = false
	) {
		try {
			if (createMongoDB ?? true) {
				await connect(process.env.DB_MONGO_CONN);
				console.log('MongoDB Connected');
			}
		} catch (error) {
			console.error(error);
			throw error;
		}
	}
}

Master process:

const worker = await spawn(
			new Worker(workerPath, {
				resourceLimits: {
					maxOldGenerationSizeMb: 32_768,
				},
			}),
			{ timeout: 30_000 }
		);
const workerResult = await worker(data);

Child worker

import { connection } from 'mongoose';
import { expose } from 'threads/worker';
import DB from '../../database';
import { ITables } from '../../models';
import { ProductModel } from '../../odm';

async function processData(data: ITables['LAGKART']['data']) {
	try {
		await new DB().init(true);
		const updates = [];
		for (const val of data) {
			if (
				val.SYS_CHANGE_OPERATION === 'I' ||
				val.SYS_CHANGE_OPERATION === 'U'
			) {
				updates.push({
					updateOne: {
						filter: { lxbenummer: val.LXBENUMMER },
						update: val.data,
						upsert: true,
					},
				});
			} else {
				updates.push({
					deleteOne: {
						filter: { lxbenummer: val.LXBENUMMER },
					},
				});
			}
		}
		const update = await ProductModel.bulkWrite(updates);

		if (update.result.writeConcernErrors.length) {
			throw update.getWriteConcernError();
		} else if (update.result.writeErrors.length) {
			throw update.getWriteErrors();
		}
	} catch (error) {
		throw error;
	} finally {
		try {
			await connection.close();
		} catch (error) {
			console.error('Connection already closed!');
		}
	}
}

expose(processData);

ProductModel

import { getModelForClass, prop } from '@typegoose/typegoose';
import { connection, Types } from 'mongoose';
class Product {
	_id: Types.ObjectId;

	@prop({ required: true, select: false })
	dataset: string;
}

const productDb = connection.useDb('dbName', { useCache: true });

const ProductModel = getModelForClass(Product, {
	existingConnection: productDb,
});

export { Product, ProductModel };

tsconfig.json

{
	"compilerOptions": {
		"baseUrl": "./src",
		"outDir": "./dist",
		"allowJs": false,
		"sourceMap": true,
		"moduleResolution": "node",
		"removeComments": true,
		"target": "ES2020",
		"module": "CommonJS",
		"experimentalDecorators": true,
		"emitDecoratorMetadata": true,
		"noImplicitAny": true,
		"esModuleInterop": true
	},
	"include": ["./src/**/*"],
	"exclude": ["node_modules", "**/node_modules/*"]
}

What is the expected behavior?
I expect it to not throw an error. Worked since typegoose 8.0.0-beta.2 and mongoose 5.12.2. Only with latest versions this breaks,

I suspect it has to do with the import "order" since:
After trial and error i can see that using dynamic import instead of import { ProductModel } from '../../odm'; i don't get this error message, but this hasn't been a problem since start of project.
Last version of typegoose + mongoose breaks this behaviour and i can't seem to find out why.

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

• System: linux / windows
• NodeJS: 14.17.6
• Typescript: 4.5.5

• Compiler / Transpiler: tsc / ts-node
• Typegoose(NPM): 9.7.0
• Typegoose(GIT): commithash
• mongoose: 6.2.3
• mongodb: 4.2.7

[SK-FComputer]

Probably occurs because of this

So i guess as @hasezoey pointed out here (typegoose/typegoose#672 (comment)), there has been an update to useDb (ad01d5e).

Why this breaks old behaviour i don't understand, and my current only solution is using dynamic imports. This is not feasible in all situations..

[SK-FComputer]

IS NOT A TYPEGOOSE ISSUE, tested with [email protected] and mongoose 6.2.1 and confirmed to work.
Only upgrade of mongoose breaks this behaviour.

Minimal reproduceable example:
https://github.com/SK-FComputer/mongoose-useDb-error

In src/worker.ts if DB() init is NOT used:

MongoDB Connected
Master update:  {
  title: 'Master',
  productID: 1,
  _id: new ObjectId("62175c1a6139f021165f602e"),
  __v: 0
}
Error [MongooseError]: Operation `products.insertOne()` buffering timed out after 10000ms
    at Timeout.<anonymous> (C:\Users\User\Desktop\mongoose-error\node_modules\mongoose\lib\drivers\node-mongodb-native\collection.js:151:23)
    at listOnTimeout (internal/timers.js:557:17)
    at processTimers (internal/timers.js:500:7)
Closing MongoDB connection master..

In src/worker.ts if DB() init is used:

MongoDB Connected
Master update:  {
  title: 'Master',
  productID: 1,
  _id: new ObjectId("62175804f97d81c206ce2ab3"),
  __v: 0
}
MongoNotConnectedError: MongoClient must be connected to perform this operation
    at getTopology (C:\Users\User\Desktop\mongoose-error\node_modules\mongodb\src\utils.ts:451:9)
    at Db.createCollection (C:\Users\User\Desktop\mongoose-error\node_modules\mongodb\src\db.ts:261:18)
    at NativeConnection.createCollection (C:\Users\User\Desktop\mongoose-error\node_modules\mongoose\lib\connection.js:404:11)
    at NativeConnection.Connection.onOpen (C:\Users\User\Desktop\mongoose-error\node_modules\mongoose\lib\connection.js:635:10)
    at NativeConnection.wireup (C:\Users\User\Desktop\mongoose-error\node_modules\mongoose\lib\drivers\node-mongodb-native\connection.js:105:13)
    at Object.onceWrapper (events.js:519:28)
    at NativeConnection.emit (events.js:400:28)
    at NativeConnection.emit (domain.js:470:12)
    at NativeConnection.set (C:\Users\User\Desktop\mongoose-error\node_modules\mongoose\lib\connection.js:126:12)
    at NativeConnection.set (C:\Users\User\Desktop\mongoose-error\node_modules\mongoose\lib\connection.js:119:23)

[IslandRhythms]

What file do I need to run? sync-data or worker?

[SK-FComputer]

@IslandRhythms sync-data.ts, should see output that it can write from master but not from worker
Also removing the DB().init() in worker, won't use connection from master.

[vkarpov15]

Fix will be in v6.2.7. We haven't been able to come up with a test case that reproduces this issue in our test suite, but I confirmed that 5bdd836 fixes the issue in your repo 👍

[SK-FComputer]

Thank you very much! @vkarpov15