get_pages() WordPress Function

function get_pages( $args = array() ) {
	global $wpdb;

	$defaults = array(
		'child_of'     => 0,
		'sort_order'   => 'ASC',
		'sort_column'  => 'post_title',
		'hierarchical' => 1,
		'exclude'      => array(),
		'include'      => array(),
		'meta_key'     => '',
		'meta_value'   => '',
		'authors'      => '',
		'parent'       => -1,
		'exclude_tree' => array(),
		'number'       => '',
		'offset'       => 0,
		'post_type'    => 'page',
		'post_status'  => 'publish',
	);

	$parsed_args = wp_parse_args( $args, $defaults );

	$number       = (int) $parsed_args['number'];
	$offset       = (int) $parsed_args['offset'];
	$child_of     = (int) $parsed_args['child_of'];
	$hierarchical = $parsed_args['hierarchical'];
	$exclude      = $parsed_args['exclude'];
	$meta_key     = $parsed_args['meta_key'];
	$meta_value   = $parsed_args['meta_value'];
	$parent       = $parsed_args['parent'];
	$post_status  = $parsed_args['post_status'];

	// Make sure the post type is hierarchical.
	$hierarchical_post_types = get_post_types( array( 'hierarchical' => true ) );
	if ( ! in_array( $parsed_args['post_type'], $hierarchical_post_types, true ) ) {
		return false;
	}

	if ( $parent > 0 && ! $child_of ) {
		$hierarchical = false;
	}

	// Make sure we have a valid post status.
	if ( ! is_array( $post_status ) ) {
		$post_status = explode( ',', $post_status );
	}
	if ( array_diff( $post_status, get_post_stati() ) ) {
		return false;
	}

	// $args can be whatever, only use the args defined in defaults to compute the key.
	$key          = md5( serialize( wp_array_slice_assoc( $parsed_args, array_keys( $defaults ) ) ) );
	$last_changed = wp_cache_get_last_changed( 'posts' );

	$cache_key = "get_pages:$key:$last_changed";
	$cache     = wp_cache_get( $cache_key, 'posts' );
	if ( false !== $cache ) {
		_prime_post_caches( $cache, false, false );

		// Convert to WP_Post instances.
		$pages = array_map( 'get_post', $cache );
		/** This filter is documented in wp-includes/post.php */
		$pages = apply_filters( 'get_pages', $pages, $parsed_args );

		return $pages;
	}

	$inclusions = '';
	if ( ! empty( $parsed_args['include'] ) ) {
		$child_of     = 0; // Ignore child_of, parent, exclude, meta_key, and meta_value params if using include.
		$parent       = -1;
		$exclude      = '';
		$meta_key     = '';
		$meta_value   = '';
		$hierarchical = false;
		$incpages     = wp_parse_id_list( $parsed_args['include'] );
		if ( ! empty( $incpages ) ) {
			$inclusions = ' AND ID IN (' . implode( ',', $incpages ) . ')';
		}
	}

	$exclusions = '';
	if ( ! empty( $exclude ) ) {
		$expages = wp_parse_id_list( $exclude );
		if ( ! empty( $expages ) ) {
			$exclusions = ' AND ID NOT IN (' . implode( ',', $expages ) . ')';
		}
	}

	$author_query = '';
	if ( ! empty( $parsed_args['authors'] ) ) {
		$post_authors = wp_parse_list( $parsed_args['authors'] );

		if ( ! empty( $post_authors ) ) {
			foreach ( $post_authors as $post_author ) {
				// Do we have an author id or an author login?
				if ( 0 == (int) $post_author ) {
					$post_author = get_user_by( 'login', $post_author );
					if ( empty( $post_author ) ) {
						continue;
					}
					if ( empty( $post_author->ID ) ) {
						continue;
					}
					$post_author = $post_author->ID;
				}

				if ( '' === $author_query ) {
					$author_query = $wpdb->prepare( ' post_author = %d ', $post_author );
				} else {
					$author_query .= $wpdb->prepare( ' OR post_author = %d ', $post_author );
				}
			}
			if ( '' !== $author_query ) {
				$author_query = " AND ($author_query)";
			}
		}
	}

	$join  = '';
	$where = "$exclusions $inclusions ";
	if ( '' !== $meta_key || '' !== $meta_value ) {
		$join = " LEFT JOIN $wpdb->postmeta ON ( $wpdb->posts.ID = $wpdb->postmeta.post_id )";

		// meta_key and meta_value might be slashed.
		$meta_key   = wp_unslash( $meta_key );
		$meta_value = wp_unslash( $meta_value );
		if ( '' !== $meta_key ) {
			$where .= $wpdb->prepare( " AND $wpdb->postmeta.meta_key = %s", $meta_key );
		}
		if ( '' !== $meta_value ) {
			$where .= $wpdb->prepare( " AND $wpdb->postmeta.meta_value = %s", $meta_value );
		}
	}

	if ( is_array( $parent ) ) {
		$post_parent__in = implode( ',', array_map( 'absint', (array) $parent ) );
		if ( ! empty( $post_parent__in ) ) {
			$where .= " AND post_parent IN ($post_parent__in)";
		}
	} elseif ( $parent >= 0 ) {
		$where .= $wpdb->prepare( ' AND post_parent = %d ', $parent );
	}

	if ( 1 === count( $post_status ) ) {
		$where_post_type = $wpdb->prepare( 'post_type = %s AND post_status = %s', $parsed_args['post_type'], reset( $post_status ) );
	} else {
		$post_status     = implode( "', '", $post_status );
		$where_post_type = $wpdb->prepare( "post_type = %s AND post_status IN ('$post_status')", $parsed_args['post_type'] );
	}

	$orderby_array = array();
	$allowed_keys  = array(
		'author',
		'post_author',
		'date',
		'post_date',
		'title',
		'post_title',
		'name',
		'post_name',
		'modified',
		'post_modified',
		'modified_gmt',
		'post_modified_gmt',
		'menu_order',
		'parent',
		'post_parent',
		'ID',
		'rand',
		'comment_count',
	);

	foreach ( explode( ',', $parsed_args['sort_column'] ) as $orderby ) {
		$orderby = trim( $orderby );
		if ( ! in_array( $orderby, $allowed_keys, true ) ) {
			continue;
		}

		switch ( $orderby ) {
			case 'menu_order':
				break;
			case 'ID':
				$orderby = "$wpdb->posts.ID";
				break;
			case 'rand':
				$orderby = 'RAND()';
				break;
			case 'comment_count':
				$orderby = "$wpdb->posts.comment_count";
				break;
			default:
				if ( 0 === strpos( $orderby, 'post_' ) ) {
					$orderby = "$wpdb->posts." . $orderby;
				} else {
					$orderby = "$wpdb->posts.post_" . $orderby;
				}
		}

		$orderby_array[] = $orderby;

	}
	$sort_column = ! empty( $orderby_array ) ? implode( ',', $orderby_array ) : "$wpdb->posts.post_title";

	$sort_order = strtoupper( $parsed_args['sort_order'] );
	if ( '' !== $sort_order && ! in_array( $sort_order, array( 'ASC', 'DESC' ), true ) ) {
		$sort_order = 'ASC';
	}

	$query  = "SELECT * FROM $wpdb->posts $join WHERE ($where_post_type) $where ";
	$query .= $author_query;
	$query .= ' ORDER BY ' . $sort_column . ' ' . $sort_order;

	if ( ! empty( $number ) ) {
		$query .= ' LIMIT ' . $offset . ',' . $number;
	}

	$pages = $wpdb->get_results( $query );

	if ( empty( $pages ) ) {
		wp_cache_set( $cache_key, array(), 'posts' );

		/** This filter is documented in wp-includes/post.php */
		$pages = apply_filters( 'get_pages', array(), $parsed_args );

		return $pages;
	}

	// Sanitize before caching so it'll only get done once.
	$num_pages = count( $pages );
	for ( $i = 0; $i < $num_pages; $i++ ) {
		$pages[ $i ] = sanitize_post( $pages[ $i ], 'raw' );
	}

	// Update cache.
	update_post_cache( $pages );

	if ( $child_of || $hierarchical ) {
		$pages = get_page_children( $child_of, $pages );
	}

	if ( ! empty( $parsed_args['exclude_tree'] ) ) {
		$exclude = wp_parse_id_list( $parsed_args['exclude_tree'] );
		foreach ( $exclude as $id ) {
			$children = get_page_children( $id, $pages );
			foreach ( $children as $child ) {
				$exclude[] = $child->ID;
			}
		}

		$num_pages = count( $pages );
		for ( $i = 0; $i < $num_pages; $i++ ) {
			if ( in_array( $pages[ $i ]->ID, $exclude, true ) ) {
				unset( $pages[ $i ] );
			}
		}
	}

	$page_structure = array();
	foreach ( $pages as $page ) {
		$page_structure[] = $page->ID;
	}

	wp_cache_set( $cache_key, $page_structure, 'posts' );

	// Convert to WP_Post instances.
	$pages = array_map( 'get_post', $pages );

	/**
	 * Filters the retrieved list of pages.
	 *
	 * @since 2.1.0
	 *
	 * @param WP_Post[] $pages       Array of page objects.
	 * @param array     $parsed_args Array of get_pages() arguments.
	 */
	return apply_filters( 'get_pages', $pages, $parsed_args );
}