WP_Query advanced post_parent

gistfile1.aw

<?php

/**
 * Advanced parent querying with WP_Query
 * 
 * This lets you do somethign like:
 */

$query = new WP_Query( array(

	'post_type' 	=> 'attachmemt',
	'post_status' 	=> 'publish',
	'post_parent' 	=> array( 
		'post_type' 	=> 'product',
		'post_status' 	=> 'draft',
		'tax_query'		=> array( array( 'taxonomy' => 'type', 'terms' => array( 'jacket' ), 'field' => 'slug' ) )
	)

) );

/**
 * I.e. get all attachments that have post_parents that are prodicts in a given taxonomy. 
 * Basically, nested queries for post_parent
 * 
 * Below is the hook. Work in progress :)
 */

add_filter( 'parse_query', function( WP_Query $wp_query ) {

	if ( empty( $wp_query->query_vars['post_parent'] ) || ! is_array( $wp_query->query_vars['post_parent'] ) )
		return;

	$wp_query->query_vars['post_parent']['showposts'] = 1;

	// Sub queries can not have SQL_CALC_FOUND_ROWS
	$wp_query->query_vars['post_parent']['no_found_rows'] = true;

	// set some stuff so we can strip it out explicitly
	$wp_query->query_vars['post_parent']['order'] = 'DESC';
	$wp_query->query_vars['post_parent']['order_by'] = 'date';

	// only select IDs as it's used in a subquery
	$wp_query->query_vars['post_parent']['fields'] = 'ids';
	
	// WP_Query is crap, so doesn't let you get the query without actually running it (which is why we set showposts = 1 above)
	$query = new WP_Query( $wp_query->query_vars['post_parent'] );

	unset( $wp_query->query_vars['post_parent'] );

	$sql = str_replace( 'ORDER BY wp_posts.post_date DESC LIMIT 0, 1' , '', $query->request );

	add_filter( 'posts_where_request', function( $where, $query ) use ( $sql, $wp_query ) {

		// blah
		if ( $query != $wp_query )
			return $where;

		global $wpdb;

		$where .= " AND $wpdb->posts.post_parent IN (" . $sql . ")";

		return $where;
	}, 10, 2 );

} );