子帖子与其父母相关（通过“post\\u parent”字段），反之亦然。因此，您必须首先查询子帖子类型，然后获取所有结果的父项。

// obviously these variable names and key names might not apply,
// change them as necessary
$performances = get_posts( array(
     \'meta_key\' => \'the_performance_date_custom_field\',
     \'meta_value\' => $date,
     \'post_type\' => \'performance\' ) );

// extract the parent post ID\'s from each of the returned performances   
$event_ids = array_map( 
     create_function(\'$post\',\'return $post->post_parent\'), 
     $performances );
$event_ids = array_unique( $event_ids ); // dump any duplicate events

// and finally, get the events from their ids
$events = get_posts( array(
    \'post_type\' => \'event\',
    \'post__in\' => $event_ids ) );