get_adjacent_post() WP 2.5.0
Gets the object of the adjacent (next or previous) post.
It is not possible to get the next and previous posts at the same time.
Return
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 a same taxonomy term.
Default: false
- $excluded_terms(array/string)
- Array or comma-separated list of excluded term IDs.
Default: ''
- $previous(true/false)
- Whether to retrieve previous post. Default true
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->ID) .'">'. $next_post->post_title .'</a>';
#2 Display the link to the previous post:
$prev_post = get_adjacent_post();
if( $prev_post )
echo '<a href="'. get_permalink($prev_post->ID) .'">'. $prev_post->post_title .'</a>';
#3 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
<?php
function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previous = true, $taxonomy = 'category' ) {
global $wpdb;
if ( ( ! $post = get_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 ( false !== strpos( $excluded_terms, ' and ' ) ) {
_deprecated_argument( __FUNCTION__, '3.3.0', sprintf( __( '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'.
*
* @since 4.4.0
*
* @param array $excluded_terms Array of excluded term IDs.
*/
$excluded_terms = apply_filters( "get_{$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 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 ( (array) $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'.
*
* @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 a same taxonomy term.
* @param array $excluded_terms Array of excluded term IDs.
* @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'.
*
* @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 a same taxonomy term.
* @param array $excluded_terms Array of excluded term IDs.
* @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'.
*
* @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";
$query_key = 'adjacent_post_' . md5( $query );
$result = wp_cache_get( $query_key, 'counts' );
if ( false !== $result ) {
if ( $result ) {
$result = get_post( $result );
}
return $result;
}
$result = $wpdb->get_var( $query );
if ( null === $result ) {
$result = '';
}
wp_cache_set( $query_key, $result, 'counts' );
if ( $result ) {
$result = get_post( $result );
}
return $result;
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