How to access instance model inside a static method in Mongoose?

I am trying to create a findOrCreate method in a mongoose model.

UserSchema.statics.findOrCreate = (newUserData, next) ->
  @findOne { id: newUserData.id }, (err, user) ->
    return next err  if err
    if not user
      self = mongoose.model 'user'
      user = new self newUserData
      user.save (err) ->
        return err if err
    next null, user

My main question is: Am I instantiating an new instance of the user model inside a static method correctly?

self = mongoose.model 'user'
user = new self newUserData

I do not see any errors, it ran without any problems. But there is no new document inserted into the database.