A Song :has and belongs to many Playlists.
I want to store additional information about a song in a given
playlist, i.e. the number of request of this song in a playlist.
Here is an example
Song A|5 requests|
Song B|3 requests|
Song A|2 requests|
Song B|4 requests|
In SQL I would add an extra column :number_of_requests to the
But how do I do it with pure ActiveRecord?