Defined (1)

The function is defined in the following location(s).

/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. 
     * 
     * @param string $order_by The `ORDER BY` clause in the SQL. 
     * @param WP_Post $post    WP_Post object. 
     */ 
    $sort = apply_filters( "get_{$adjacent}_post_sort", "ORDER BY p.post_date $order LIMIT 1", $post ); 
 
    $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; 
}