public function createTemporaryCopy()
    {
        if ( $this->attribute( 'original_id' ) === 0 )
            throw new Exception( 'eZPolicy #' . $this->attribute( 'id' ) . ' is already a temporary item (original: #'. $this->attribute( 'original_id' ) . ')' );

        $policyCopy = self::copy( $this->attribute( 'role_id' ) );
        $policyCopy->setAttribute( 'original_id', $this->attribute( 'id' ) );
        $policyCopy->store();

        return $policyCopy;
    }