Given then, how would you map a search that returns multiple types?
As far as deleting songs "safely", what Ian means is that for any given playlist (of which a user has an unlimited number) any given song can be in it any number of times. So when you delete a song, we generally ask for song_id and index to make sure that a) the playlist hasn't mutated (much), and b) we are dropping the right song. The DELETE on /{trashbin uri}/{song id} doesn't provide 2 of the 3 required bits of information, and DELETE /playlist/{playlist id}/{song id}/{index} isn't very RESTful (imo).
As far as deleting songs "safely", what Ian means is that for any given playlist (of which a user has an unlimited number) any given song can be in it any number of times. So when you delete a song, we generally ask for song_id and index to make sure that a) the playlist hasn't mutated (much), and b) we are dropping the right song. The DELETE on /{trashbin uri}/{song id} doesn't provide 2 of the 3 required bits of information, and DELETE /playlist/{playlist id}/{song id}/{index} isn't very RESTful (imo).