How to fix MongoError: Cannot use a session that has ended

Question

I'm trying to read data from a MongoDB Atlas collection using Node.js. When I try to read the contents of my collection I get the error MongoError: Cannot use a session that has ended. Here is my code

client.connect(err => {
    const collection = client
        .db("sample_airbnb")
        .collection("listingsAndReviews");

    const test = collection.find({}).toArray((err, result) => {
        if (err) throw err;
    });
    client.close();
});

I'm able to query for a specific document, but I'm not sure how to return all documents of a collection. I've searched for this error, I can't find much on it. Thanks

Answer 1

In your code, it doesn't wait for the find() to complete its execution and goes on to the client.close() statement. So by the time it tries to read data from the db, the connection has already ended. I faced this same problem and solved it like this:

// connect to your cluster
const client = await MongoClient.connect('yourMongoURL', { 
    useNewUrlParser: true, 
    useUnifiedTopology: true,
});
// specify the DB's name
const db = client.db('nameOfYourDB');
// execute find query
const items = await db.collection('items').find({}).toArray();
console.log(items);
// close connection
client.close();

EDIT: this whole thing should be in an async function.

Answer 2

Ran into the same issue when I updated the MongoClient from 3.3.2 to the latest version (3.5.2 as of this writing.) Either install only 3.3.2 version by changing the package.json "mongodb": "3.3.2", or just use async and await wrapper.

If still the issue persists, remove the node_modules and install again.