Promises

Built-in Promises

Mongoose async operations, like .save() and queries, return thenables. This means that you can do things like MyModel.findOne({}).then() and await MyModel.findOne({}).exec() if you're using async/await.

You can find the return type of specific operations in the api docs You can also read more about promises in Mongoose.

[require:Built-in Promises]

Queries are not promises

Mongoose queries are not promises. They have a .then() function for co and async/await as a convenience. If you need a fully-fledged promise, use the .exec() function.

[require:Queries are not promises]

Queries are thenable

Although queries are not promises, queries are thenables. That means they have a .then() function, so you can use queries as promises with either promise chaining or async await

[require:Queries are thenable]

Should You Use exec() With await?

There are two alternatives for using await with queries:

• await Band.findOne();
• await Band.findOne().exec();

As far as functionality is concerned, these two are equivalent. However, we recommend using .exec() because that gives you better stack traces.

[require:Should You Use `exec\(\)` With `await`]

Plugging in your own Promises Library

If you're an advanced user, you may want to plug in your own promise library like bluebird. Just set mongoose.Promise to your favorite ES6-style promise constructor and mongoose will use it.

[require:Plugging in your own Promises Library]