public function key()
    {
        $file = $this->current();
        return ($file !== null) ? (string) $file->file['_id'] : null;
    }
public function key()
    {
        $file = $this->current();
        return ($file !== null) ? (string) $file->file['_id'] : null;
    }
public function key ( ) { $ file = $ this -> current ( ) ; return ( $ file !== null ) ? ( string ) $ file -> file [ '_id' ] : null ; }
Returns the current result's filename

@link http://php.net/manual/en/mongogridfscursor.key.php
@return string The current results filename
Returns the current result s filename