public function orderBy( $columns, $direction = 'asc' ) { // @codingStandardsIgnoreLine
		if ( is_string( $columns ) ) {
			$columns = $this->argument_to_array( $columns );
		}

		foreach ( $columns as $key => $column ) {
			if ( is_numeric( $key ) ) {
				$this->statements['orders'][ $column ] = $direction;
			} else {
				$this->statements['orders'][ $key ] = $column;
			}
		}

		return $this;
	}