MongoDB via Mongoose JS - What is findByID?

I am writing a NodeJS server with ExpressJS, PassportJS, MongoDB and MongooseJS. I just managed to get PassportJS to use user data obtained via Mongoose to authenticate.

But to make it work, I had to use a "findById" function like below.

var UserModel = db.model('User',UserSchema);

UserModel.findById(id, function (err, user) { < SOME CODE > } );

UserModel is a Mongoose model. I declare the schema, UserSchema earlier. So I suppose UserModel.findById() is a method of the Mongoose model?

Question

What does findById do and is there documentation on it? I googled around a bit but didn't find anything.

findById is a convenience method on the model that's provided by Mongoose to find a document by its _id. The documentation for it can be found here.

Example:

// Search by ObjectId
var id = "56e6dd2eb4494ed008d595bd";
UserModel.findById(id, function (err, user) { ... } );

Functionally, it's the same as calling:

UserModel.findOne({_id: id}, function (err, user) { ... });

Note that Mongoose will cast the provided id value to the type of _id as defined in the schema (defaulting to ObjectId).

If the schema of id is not of type ObjectId you cannot operate with function : findbyId()

As opposed to find() which can return 1 or more documents, findById() can only return 0 or 1 document. Document(s) can be thought of as record(s).

I'm the maintainer of Mongoose. findById() is a built-in method on Mongoose models. findById(id) is equivalent to findOne({ _id: id }), with one caveat: findById() with 0 params is equivalent to findOne({ _id: null }).

You can read more about findById() on the Mongoose docs and this findById() tutorial.