How to use methods containing mongoose functions with control flow frameworks (e.g. Async or Step)

I am struggling a little with how to call asynchronous functions in a serial manner. In particular, functions which incorporate mongoose calls to the database. I have a class definition which includes two methods: (MovieFile.exists) checks if a certain record exists in the database; (MovieFile.save) saves a record in the database. Ideally I want to be able to save the record (MovieFile.save()) after confirming whether or not it exists in the database (MovieFile.exists()).

Ideally I want to do something like this:

// Create instance of MovieFile object.  
var movieFile = new MovieFile(mongoose);
if (movieFile.exists() === false) {
  movieFile.save();
}

Unfortunately the asynchronous nature on mongoose makes this not possible. I have been playing around with Step and Async control flow frameworks. Unfortunately I just can't get my head around how to use such frameworks in this case. I would be grateful if someone could tell me how to put the above code into either Step or Async. I think the issue is that the asynchronous mongoose calls are themselves embedded within a method (See: MovieFile.exists and MovieFile.save). I realise that use of such a framework may be overkill in this example, but I am trying to use this as a learning exercise.

function MovieFile(mongoose) {
  var Movie = mongoose.model('Movie');

  this.exists = function() {
    // Confirm necessary object variables have been set.
    if (typeof this.originalFileName === 'undefined') {
      throw error = new Error('Variable originalFilename has not been set for MovieFile.');
    }
    if (typeof this.fileSize !== 'number') {
      throw error = new Error('Variable originalFilename has not been set for MovieFile.');
    }
    // Check database for existing record.
    Movie
      .find({ originalFileName: this.originalFileName, size: this.fileSize })
      .exec(function(error, results) {
        if (error) {
          throw error;
        }
        else if (results.length === 0) {
          return false;
        }
        else if (results.length === 1) {
          return true;
        }
        else {
          throw error = new Error('More than one record for this movie record exists.');
        }
      });
  };

  this.save = function() {
    // save movie to database.
    var values = {
      name: this.getName(),
      machineFileName: this.getMachineFileName(),
      originalFileName: this.getName(),
      size: this.getFileSize(),
    };
    var movie = new Movie(values);
    movie.save(function(error, data) {
      if (error) {
        console.log(error);
      }
      else {
        console.log('Movie saved.');
      }
    });
  };
};