createIndex in mongoose

createIndex is a function for Mongodb.

In Mongoose it is renamed to index

Item.index({ "createdAt": 1 }, { expireAfterSeconds: 3600 })

Two ways to create index. First

const Schema = mongoose.Schema;
let user = new Schema({
    email: {
        type: String,
        required: true,
        index: true       //---Index----
    }
});
module.exports = mongoose.model('User', user);

Second method

const Schema = mongoose.Schema;
let user = new Schema({
    email: {
        type: String,
        required: true
    }
});
user.index({ email: 1 });    //---Index----
module.exports = mongoose.model('User', user);

When doing this if you are getting a warning(I am using MongoDB: 4.2.8 and Mongoose: 5.9.20)

DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes instead.

Then you might need to add 'useCreateIndex: true' to your mongoose.connect

mongoose.connect(Uri, {
    useNewUrlParser: true,
    useUnifiedTopology: true, 
    useCreateIndex: true
});