How to check if a collection exists in Mongodb native nodejs driver?

Question

I need to check if a collection exists on a certain database and create it if it doesn't. I know that

db.createCollection(collName, {strict:true}, function(error, collection))

checks for existance of collection collName before creating it and sets error object. but I need an independent function to check that.

Answer 1

The collectionNames method of the native driver's Db object accepts an optional collection name filter as a first parameter to let you check the existence of a collection:

db.collectionNames(collName, function(err, names) {
    console.log('Exists: ', names.length > 0);
});

In the 2.x version of the MongoDB native driver, collectionNames has been replaced by listCollections which accepts a filter and returns a cursor so you would do this as:

db.listCollections({name: collName})
    .next(function(err, collinfo) {
        if (collinfo) {
            // The collection exists
        }
    });

Answer 2

Using mongo-native driver and Node.js 7.6+, I use the following:

const collections = await db.collections();
if (!collections.map(c => c.s.name).includes(collName)) {
    await db.createCollection(collName);
}

EDIT

As @MattCochrane mentions, collection.s.name is no longer available; as @JohnnyHK and @weekens point out, the correct way is to use the listCollections() method:

const client = new MongoClient(connectionString, { useUnifiedTopology: true });
await client.connect();
const collections = await client.db().listCollections().toArray();
const collectionNames = collections.map(c => c.name);

listCollection() takes an optional filter.