code: function( model, options ) {
  			if ( this.related ) {
  				return;
  			}
  			options = this.sanitizeOptions( options );
  			
  			var item = this.keyContents;
  			if ( item && ( _.isString( item ) || _.isNumber( item ) || typeof( item ) === 'object' ) ) {
  				var id = _.isString( item ) || _.isNumber( item ) ? item : item[ this.relatedModel.prototype.idAttribute ];
  				if ( model.id === id ) {
  					this.addRelated( model, options );
  				}
  			}
  		}
docs: If a new 'this.relatedModel' appears in the 'store', try to match it to the last set 'keyContents'