Duplicate Mongoose log entry when using promises

Question

I've implemented promises into mongoose but I'm receiving duplicate log entries and I'm not sure if it's the expected output and if so, why?

I run the below function, only once during an if statement.

const isUsernameTaken = (username) => {
  let isTaken;
  const promise = User.find({username: username}, (err, doc) => {
    if(doc.length) {
      isTaken = true;
    } else {
      isTaken = false;
    }
  }).exec();
  promise.then(() => {
    return isTaken;
  });
}

mongoose debug output

Mongoose: users.find({username: 'test'}, {projection: {}})
Mongoose: users.find({username: 'test'}, {projection: {}})
true

vs what I would expect

Mongoose: users.find({username: 'test'}, {projection: {}})
true

Answer 1

It looks like using a callback for find, as well as calling exec() is sending the request twice... Putting the callback inside of promise.then(...) should fix it:

const isUsernameTaken = (username) => {
  User.find({username: username})
    .exec()
    .then(doc => doc ? true : false)
    .catch(err => console.log(err));
}