Why do I get the Must call setClient() with an instance of MongoClient error ?

[robots4life]

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.

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);

	console.log(client);

        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. However it logs the client just fine, so I am not sure what I am doing wrong. How do I use setClient() correctly please ?

From what I understand is that I can use setClient to set the Mongoose client to the client that established a connection with MongoDB with the native driver, is this correct at all or have I got this wrong ? If so, what does setClient do exactly ?

[vkarpov15]

The error message I get when running the above script is:

MongooseError: Cannot call `setClient()` with a MongoClient that you have not called `connect()` on yet.

Which is fairly self explanatory, you need to do await client.connect() before calling setClient().

The error message you posted, though, makes me think that you have an incompatible version of the mongodb driver. Try running npm list | grep "mongo" and paste the output here. The output should look something like:

projectname@0.0.2 /home/user/projectname
└─┬ mongoose@6.2.5
  ├─┬ mongodb@4.3.1
  │ ├─┬ mongodb-connection-string-url@2.5.2

[Uzlopak]

mongodb is not a devDependency but a dependency. There is actually no need to add mongodb as a dependency next to mongoose in your project.

[robots4life]

@Uzlopak

There is actually no need to add mongodb as a dependency next to mongoose in your project.

Why ?

This is useful if you already have a MongoClient instance, and want to reuse it.

Without including mongodb I cannot do https://github.com/robots4life/mongo-mongoose/blob/master/src/routes/index.js#L3 or https://github.com/robots4life/mongo-mongoose/blob/master/src/routes/index.js#L10.

[Uzlopak]

If you use mongoose as a dependency, then npm looks for its dependencies and installs them in the root of node_modules. So if you only use mongoose as a dependency it will put the mongodb package in the root of node_modules. If you use mongodb as a package next to mongoose, npm checks if they are matching versions. If they dont match, then npm installs the one specified in your package.json under node_modules/mongodb and the one from mongoose into node_modules/mongoose/node_modules/mongodb.

If you use mongoose, which has mongodb as dependency, and another package, which has mongodb as a depenendency, then npm installs mongodb not on root level but in separate node_modules of each package, like mongoose/node_modules/mongodb and other_package/node_modules/mongodb.

This is also what you wrote in your comment.

Actually: Why dont you let mongoose handle the connection? Why do you separately create the client and connect it to mongoose?

[robots4life]

@vkarpov15 What @Uzlopak wrote here #11494 (reply in thread) would be good to have in the docs perhaps. For me this was not apparent.

@Uzlopak To your question, a) I don't always need mongoose and b) I wanted to learn how to get https://mongoosejs.com/docs/api/connection.html#connection_Connection-setClient to work in cases where I want to use mongoose while already having a mongodb connection.

Something else given your detailed explanation.
When I just do npm install mongoose --save in a new project, will I still have mongodb npm package available and still be able to do https://github.com/robots4life/mongo-mongoose/blob/master/src/routes/index.js#L3 without explicitly having installed mongodb ? Have I understood this correct from your comment ?

[Uzlopak]

Yes: