描述
获取上一篇或下一篇相邻的文章。
语法
get_adjacent_post( bool $in_same_term = false, array|string $excluded_terms = '', bool $previous = true, string $taxonomy = 'category' )参数
$in_same_term：(bool) (Optional)( Default value: false) 文章是否在同一分类
$excluded_terms：(array|string) (Optional) (Default value: '') 排除分类的ID
$previous：(boolean) (Optional) (Default value: true) 是否获取上一篇文章
$taxonomy：(string) (Optional)(Default value: 'category') 如果 $in_same_term 设置为 表示限定的分类
返回值
WP_Post：如果成功，返回文章对 象。
Null：如果 global $post 没有设置，返回空值Null。
String：如果不存在符合条件的文章 ，返回空字符串。
示例
获取同分类下的上一篇文章。
<?php $prev_post = get_adjacent_post( true, '', true, 'taxonomy_slug' ); ?>
<?php if ( is_a( $prev_post, 'WP_Post' ) ) { ?>
<a href="<?php echo get_permalink( $prev_post->ID ); ?>"><?php echo get_the_title( $prev_post->ID ); ?></a>
<?php } ?>获取同分类下的下一篇文章。
<?php $next_post = get_adjacent_post( true, '', false, 'taxonomy_slug' ); ?>
<?php if ( is_a( $next_post, 'WP_Post' ) ) { ?>
<a href="<?php echo get_permalink( $next_post->ID ); ?>"><?php echo get_the_title( $next_post->ID ); ?></a>
<?php } ?>关系
被用
wp-includes/link-template.php: get_adjacent_post_link()
wp-includes/link-template.php: get_previous_post()
wp-includes/link-template.php: get_next_post()
wp-includes/link-template.php: get_adjacent_post_rel_link()
源码
位置： wp-includes/link-template.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 ( $in_same_term || ! empty( $excluded_terms ) ) {
if ( ! empty( $excluded_terms ) && ! is_array( $excluded_terms ) ) {
// back-compat, $excluded_terms used to be $excluded_terms 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 );
}
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( ',', $term_array ) . ")";
}
/**
* Filters the IDs of terms excluded from adjacent post queries.
*
* The dynamic portion of the hook name, `$adjacent`, refers to the type
* of adjacency, 'next' or 'previous'.
*
* @since 4.4.0
*
* @param string $excluded_terms Array of excluded term IDs.
*/
$excluded_terms = apply_filters( "get_{$adjacent}_post_excluded_terms", $excluded_terms );
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;
}