Mongoose - What does the exec function do?

Question

I came across a piece of Mongoose code that included a query findOne and then an exec() function.

I've never seen that method in Javascript before? What does it do exactly?

Answer 1

To understand the exec function basically when using mongoose, documents can be retrieved using helpers. Every model method that accepts query conditions can be executed by means of a callback or the exec method.

callback:

User.findOne({ name: 'daniel' }, function (err, user) { 

// 

});

exec:

User .findOne({ name: 'daniel' }) .exec(function (err, user) { // 

});

Answer 2

The following design is very handy and generic - it can handle callbacks or promises accurately:

function findAll(query, populate, cb) {

  let q = Response.find(query);

  if (populate && populate.length > 0) {

    q = q.populate(populate);

  }

  // cb is optional and it will return promise if cb == null

  return q.lean().exec(cb);

}