Why does Mongoose setClient return MongooseError: Must call `setClient()` with an instance of MongoClient? - mongodb

Question

I am having trouble getting setClient() to work. My understanding of this is, that I can make a connection to MongoDB with the native MongoDB MongoClient and then in another piece of code I should be able to use this instance of the MongoClient to connect to Mongoose. So set the client to Mongoose while using the same identical connection, not a separate one.
https://mongoosejs.com/docs/api/connection.html#connection_Connection-setClient
Set the MongoDB driver MongoClient instance that this connection uses to talk to MongoDB. This is useful if you already have a MongoClient instance, and want to reuse it.
Case A
import mongoose from 'mongoose';
import { MongoClient } from 'mongodb';
async function run() {
try {
const uri = 'mongodb://localhost:27017';
// Create a new MongoClient
const client = new MongoClient(uri);
const conn = mongoose.createConnection().setClient(client);
conn.getClient(); // MongoClient { ... }
conn.readyState; // 1, means 'CONNECTED'
} catch (error) {
console.log(error);
}
}
run();
This returns
MongooseError: Must call setClient() with an instance of MongoClient at NativeConnection.setClient (.../node_modules/mongoose/lib/connection.js:1391:11).
Why am I getting this error ? What is the correct code for setClient()?
Case B
Vercel shows how to used MongoDB and Mongoose in their environment exporting a clientPromise here with MongoDB https://github.com/vercel/next.js/blob/canary/examples/with-mongodb/lib/mongodb.js and a dbConnect here with Mongoose https://github.com/vercel/next.js/blob/canary/examples/with-mongodb-mongoose/lib/dbConnect.js.
So given in db.js I have this exemplary code with the native MongoDB driver
import { MongoClient } from 'mongodb'
const uri = process.env.MONGODB_URI
const options = {}
let client
let clientPromise
if (!process.env.MONGODB_URI) {
throw new Error('Please add your Mongo URI to .env.local')
}
if (process.env.NODE_ENV === 'development') {
// In development mode, use a global variable so that the value
// is preserved across module reloads caused by HMR (Hot Module Replacement).
if (!global._mongoClientPromise) {
client = new MongoClient(uri, options)
global._mongoClientPromise = client.connect()
}
clientPromise = global._mongoClientPromise
} else {
// In production mode, it's best to not use a global variable.
client = new MongoClient(uri, options)
clientPromise = client.connect()
}
// Export a module-scoped MongoClient promise. By doing this in a
// separate module, the client can be shared across functions.
export default clientPromise
and in another file I like to use this clientPromise with Mongoose what do I do ?
Is my understanding correct here that I in fact can use the exported MongoDB clientPromise with Mongoose at all through the use of setClient() ? Or is setClient() used for something different ?
In another file, if I try this
import mongoose from 'mongoose';
import clientPromise from '$lib/mongodb';
export async function get() {
try {
const client = await clientPromise;
console.log(client); // logs client just fine
const conn = mongoose.createConnection().setClient(client);
// starts complaining here with
// MongooseError: Must call `setClient()` with an instance of MongoClient
conn.getClient(); // MongoClient { ... }
conn.readyState; // 1, means 'CONNECTED'
console.log(conn);
return {
status: 200,
body: {
message: 'ok'
}
};
} catch (error) {
console.log(error);
}
}
the same error is shown.
How do I get setClient() to work on either, the MongoClient instance or the clientPromise?
edit:
I also get this error.
Argument of type 'import(".../node_modules/mongodb/mongodb").MongoClient' is not assignable to parameter of type 'import(".../node_modules/mongoose/node_modules/mongodb/mongodb").MongoClient'.
The types of 'options.credentials' are incompatible between these types.
Type 'import(".../node_modules/mongodb/mongodb").MongoCredentials' is not assignable to type 'import(".../node_modules/mongoose/node_modules/mongodb/mongodb").MongoCredentials'.