Favorite and playlist models

app/models/favorite.rb

@@ -0,0 +1,6 @@
+class Favorite < ActiveRecord::Base
+  belongs_to :user
+  belongs_to :artist
+  belongs_to :album
+  belongs_to :track
+end

app/models/playlist.rb

@@ -0,0 +1,4 @@
+class Playlist < ActiveRecord::Base
+  belongs_to :user
+  has_many :playlist_tracks
+end

app/models/playlist_item.rb

@@ -0,0 +1,4 @@
+class PlaylistItem < ActiveRecord::Base
+  belongs_to :playlist
+  belongs_to :track
+end