code: function(model)
    {
      var exists = this.has( model.$key() );
      var matches = this.filter( model );
  
      if ( exists && !matches )
      {
        this.remove( model );
      }
      if ( !exists && matches )
      {
        this.add( model );
      }
    }
docs: Handles the ModelUpdated event from the database.