get_adjacent_post() │ WP 2.5.0

Gets the object of the adjacent (next or previous) post from the specified taxonomy (the default is category).

It is not possible to get the next and previous posts at the same time.

Used By: get_previous_post(), get_next_post(), get_adjacent_post_link()

Hooks from the function

get_(adjacent)_post_excluded_terms

get_next_post_excluded_terms

get_previous_post_excluded_terms

get_(adjacent)_post_join

get_next_post_join

get_previous_post_join

get_(adjacent)_post_where

get_next_post_where

get_previous_post_where

get_(adjacent)_post_sort

get_next_post_sort

get_previous_post_sort

Return

WP_Post|null|String.

WP_Post - Post object in case of success;
Null - if the global variable $post is not set;
Empty string - if there is no suitable post.

Usage

get_adjacent_post( $in_same_term, $excluded_terms, $previous, $taxonomy );

$in_same_term(true|false): Whether post should be in the same taxonomy term.
Default: false
$excluded_terms(int[]|string): Array or comma-separated list of excluded term IDs.
Default: empty string
$previous(true|false): Whether to retrieve previous post.
Default: true
$taxonomy(string): Taxonomy, if $in_same_term is true.
Default: 'category'

Examples

#1 Display the link to the next post:

$next_post = get_adjacent_post( 0, '', 0 );
if( $next_post ){
	echo '<a href="'. get_permalink( $next_post ) .'">'. get_the_title( $next_post ) .'</a>';
}

Display the link to the previous post:

$prev_post = get_adjacent_post();
if( $prev_post ){
	echo '<a href="'. get_permalink( $prev_post ) .'">'. get_the_title( $prev_post ) .'</a>';
}

#2 Return data

Example of the object that the function return:

[ID]            => 25
[post_author]   => 1
[post_date]     => 2010-04-05 04:24:04
[post_date_gmt] => 2010-04-05 00:24:04
[post_content]  => If you have something to discuss, go through the keyboard on the form below:
[post_title]    => Feedback
[post_excerpt]  =>
[post_status]   => publish
[comment_status] => closed
[ping_status]    => closed
[post_password]  =>
[post_name] => contacts
[to_ping]   =>
[pinged]    =>
[post_modified]     => 2010-08-16 17:41:20
[post_modified_gmt] => 2010-08-16 13:41:20
[post_content_filtered] =>
[post_parent] => 0
[guid]        => https://wp-kama.com/contacts
[menu_order]  => 0
[post_type]   => page
[post_mime_type] =>
[comment_count]  => 0

Notes

Global. wpdb. $wpdb WordPress database abstraction object.

Changelog

Since 2.5.0

Introduced.

`get_adjacent_post() get adjacent post` code ^{WP 6.7.1}

wp-includes/link-template.php

function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previous = true, $taxonomy = 'category' ) {
	global $wpdb;

	$post = get_post();

	if ( ! $post || ! taxonomy_exists( $taxonomy ) ) {
		return null;
	}

	$current_post_date = $post->post_date;

	$join     = '';
	$where    = '';
	$adjacent = $previous ? 'previous' : 'next';

	if ( ! empty( $excluded_terms ) && ! is_array( $excluded_terms ) ) {
		// Back-compat, $excluded_terms used to be $excluded_categories with IDs separated by " and ".
		if ( str_contains( $excluded_terms, ' and ' ) ) {
			_deprecated_argument(
				__FUNCTION__,
				'3.3.0',
				sprintf(
					/* translators: %s: The word 'and'. */
					__( 'Use commas instead of %s to separate excluded terms.' ),
					"'and'"
				)
			);
			$excluded_terms = explode( ' and ', $excluded_terms );
		} else {
			$excluded_terms = explode( ',', $excluded_terms );
		}

		$excluded_terms = array_map( 'intval', $excluded_terms );
	}

	/**
	 * Filters the IDs of terms excluded from adjacent post queries.
	 *
	 * The dynamic portion of the hook name, `$adjacent`, refers to the type
	 * of adjacency, 'next' or 'previous'.
	 *
	 * Possible hook names include:
	 *
	 *  - `get_next_post_excluded_terms`
	 *  - `get_previous_post_excluded_terms`
	 *
	 * @since 4.4.0
	 *
	 * @param int[]|string $excluded_terms Array of excluded term IDs. Empty string if none were provided.
	 */
	$excluded_terms = apply_filters( "get_{$adjacent}_post_excluded_terms", $excluded_terms );

	if ( $in_same_term || ! empty( $excluded_terms ) ) {
		if ( $in_same_term ) {
			$join  .= " INNER JOIN $wpdb->term_relationships AS tr ON p.ID = tr.object_id INNER JOIN $wpdb->term_taxonomy AS tt ON tr.term_taxonomy_id = tt.term_taxonomy_id";
			$where .= $wpdb->prepare( 'AND tt.taxonomy = %s', $taxonomy );

			if ( ! is_object_in_taxonomy( $post->post_type, $taxonomy ) ) {
				return '';
			}
			$term_array = wp_get_object_terms( $post->ID, $taxonomy, array( 'fields' => 'ids' ) );

			// Remove any exclusions from the term array to include.
			$term_array = array_diff( $term_array, (array) $excluded_terms );
			$term_array = array_map( 'intval', $term_array );

			if ( ! $term_array || is_wp_error( $term_array ) ) {
				return '';
			}

			$where .= ' AND tt.term_id IN (' . implode( ',', $term_array ) . ')';
		}

		if ( ! empty( $excluded_terms ) ) {
			$where .= " AND p.ID NOT IN ( SELECT tr.object_id FROM $wpdb->term_relationships tr LEFT JOIN $wpdb->term_taxonomy tt ON (tr.term_taxonomy_id = tt.term_taxonomy_id) WHERE tt.term_id IN (" . implode( ',', array_map( 'intval', $excluded_terms ) ) . ') )';
		}
	}

	// 'post_status' clause depends on the current user.
	if ( is_user_logged_in() ) {
		$user_id = get_current_user_id();

		$post_type_object = get_post_type_object( $post->post_type );
		if ( empty( $post_type_object ) ) {
			$post_type_cap    = $post->post_type;
			$read_private_cap = 'read_private_' . $post_type_cap . 's';
		} else {
			$read_private_cap = $post_type_object->cap->read_private_posts;
		}

		/*
		 * Results should include private posts belonging to the current user, or private posts where the
		 * current user has the 'read_private_posts' cap.
		 */
		$private_states = get_post_stati( array( 'private' => true ) );
		$where         .= " AND ( p.post_status = 'publish'";
		foreach ( $private_states as $state ) {
			if ( current_user_can( $read_private_cap ) ) {
				$where .= $wpdb->prepare( ' OR p.post_status = %s', $state );
			} else {
				$where .= $wpdb->prepare( ' OR (p.post_author = %d AND p.post_status = %s)', $user_id, $state );
			}
		}
		$where .= ' )';
	} else {
		$where .= " AND p.post_status = 'publish'";
	}

	$op    = $previous ? '<' : '>';
	$order = $previous ? 'DESC' : 'ASC';

	/**
	 * Filters the JOIN clause in the SQL for an adjacent post query.
	 *
	 * The dynamic portion of the hook name, `$adjacent`, refers to the type
	 * of adjacency, 'next' or 'previous'.
	 *
	 * Possible hook names include:
	 *
	 *  - `get_next_post_join`
	 *  - `get_previous_post_join`
	 *
	 * @since 2.5.0
	 * @since 4.4.0 Added the `$taxonomy` and `$post` parameters.
	 *
	 * @param string       $join           The JOIN clause in the SQL.
	 * @param bool         $in_same_term   Whether post should be in the same taxonomy term.
	 * @param int[]|string $excluded_terms Array of excluded term IDs. Empty string if none were provided.
	 * @param string       $taxonomy       Taxonomy. Used to identify the term used when `$in_same_term` is true.
	 * @param WP_Post      $post           WP_Post object.
	 */
	$join = apply_filters( "get_{$adjacent}_post_join", $join, $in_same_term, $excluded_terms, $taxonomy, $post );

	/**
	 * Filters the WHERE clause in the SQL for an adjacent post query.
	 *
	 * The dynamic portion of the hook name, `$adjacent`, refers to the type
	 * of adjacency, 'next' or 'previous'.
	 *
	 * Possible hook names include:
	 *
	 *  - `get_next_post_where`
	 *  - `get_previous_post_where`
	 *
	 * @since 2.5.0
	 * @since 4.4.0 Added the `$taxonomy` and `$post` parameters.
	 *
	 * @param string       $where          The `WHERE` clause in the SQL.
	 * @param bool         $in_same_term   Whether post should be in the same taxonomy term.
	 * @param int[]|string $excluded_terms Array of excluded term IDs. Empty string if none were provided.
	 * @param string       $taxonomy       Taxonomy. Used to identify the term used when `$in_same_term` is true.
	 * @param WP_Post      $post           WP_Post object.
	 */
	$where = apply_filters( "get_{$adjacent}_post_where", $wpdb->prepare( "WHERE p.post_date $op %s AND p.post_type = %s $where", $current_post_date, $post->post_type ), $in_same_term, $excluded_terms, $taxonomy, $post );

	/**
	 * Filters the ORDER BY clause in the SQL for an adjacent post query.
	 *
	 * The dynamic portion of the hook name, `$adjacent`, refers to the type
	 * of adjacency, 'next' or 'previous'.
	 *
	 * Possible hook names include:
	 *
	 *  - `get_next_post_sort`
	 *  - `get_previous_post_sort`
	 *
	 * @since 2.5.0
	 * @since 4.4.0 Added the `$post` parameter.
	 * @since 4.9.0 Added the `$order` parameter.
	 *
	 * @param string $order_by The `ORDER BY` clause in the SQL.
	 * @param WP_Post $post    WP_Post object.
	 * @param string  $order   Sort order. 'DESC' for previous post, 'ASC' for next.
	 */
	$sort = apply_filters( "get_{$adjacent}_post_sort", "ORDER BY p.post_date $order LIMIT 1", $post, $order );

	$query        = "SELECT p.ID FROM $wpdb->posts AS p $join $where $sort";
	$key          = md5( $query );
	$last_changed = wp_cache_get_last_changed( 'posts' );
	if ( $in_same_term || ! empty( $excluded_terms ) ) {
		$last_changed .= wp_cache_get_last_changed( 'terms' );
	}
	$cache_key = "adjacent_post:$key:$last_changed";

	$result = wp_cache_get( $cache_key, 'post-queries' );
	if ( false !== $result ) {
		if ( $result ) {
			$result = get_post( $result );
		}
		return $result;
	}

	$result = $wpdb->get_var( $query );
	if ( null === $result ) {
		$result = '';
	}

	wp_cache_set( $cache_key, $result, 'post-queries' );

	if ( $result ) {
		$result = get_post( $result );
	}

	return $result;
}