code: function( key, callback ) {
              var me = this;
              root( this, function( store ) {
                  store.getFile( key, {create:false}, function() {
                      if ( callback ) me.lambda( callback ).call( me, true );
                  }, function() {
                      if ( callback ) me.lambda( callback ).call( me, false );
                  });
              });
              return this;
          }
docs: check if an obj exists in the collection