NoMethodError for ActiveRecord

I created 3 models that are each related to each other, a playlist model, an artist model, and a song model. In my controller, there is no issue to create a new entry in the Playlist table, but when I attempt to do the same in the Artist, or Song table, a no method error is raised:

undefined method create' for UploadController::Artist:Class

I am terribly confused as to how this is possible because there should be no difference between the three models, and how the controller interacts with them should there?

If anyone can help, I would greatly appreciate it, thanks!