app/assets/javascripts/models/fileitem.js in mix-rails-albums-0.22.0 vs app/assets/javascripts/models/fileitem.js in mix-rails-albums-0.23.0

@@ -1,8 +1,7 @@
 var FileItem = Backbone.Model.extend({
     name: 'photo',
     url: 'photos',
-    idAttribute: '_id',
     defaults: {
         progress:0
     },
     initialize: function(){
         this.on('add', this.onAdd, this);
\ No newline at end of file