How to run WP_Query to retrieve attachments to posts only from a particular category?

Question

I have a WP blog with a few pages and posts and several categories. I want to write a loop to retrieve images attached to the posts (not the pages) and only those from a specific category and it's children. The category id is 60.

This is the WP_Query call:

$my_query = new WP_Query( array(
  'post_type' => 'attachment',
  'cat' => '60',
  'post_mime_type' =>'image',
  'posts_per_page' => $batch_size,
  'nopaging' => false,
  'post_status' => 'all',
  'post_parent' => null,
  'meta_key' => 'my_hash',
  'orderby' => 'meta_value'
) );

But I get nothing!

What am I doing wrong?

Answer 1

You'll need to first grab the posts, then grab the attachments that are children of said posts.

$my_query = new WP_Query( array(
    'meta_key' => 'my_hash',
    'nopaging' => true,
    'orderby' => 'meta_value',
    'fields' => 'ids',
    'cat' => '60',
));

if ( $post_ids = $my_query->get_posts() ) {
    $post_ids = implode( ',', $post_ids );
    $atts_ids = $wpdb->get_col( "SELECT ID FROM $wpdb->posts WHERE post_parent IN($post_ids) AND post_type = 'attachment'" );   

    $my_query->query( array(
        'posts_per_page' => $batch_size,
        'post_mime_type' =>'image',
        'post_status' => 'all',
        'post_type' => 'attachment',
        'post__in' => $atts_ids,
    ));
}

Answer 2

Attachment posts don't have categories, their parents 'post' posts do, so you have a two step problem.

• Find the IDs of the posts of type post in the category ( 60? )
• Find the attachments that have a post_parent that is in the list we found in our first query

Answer 3

If you want to get image links frop category and subcategories you should use this:

    global $wpdb;
$id = 60; // your cat id
$myrows = $wpdb->get_results( "SELECT p2.ID, p2.guid ".
    "FROM $wpdb->posts as p1, $wpdb->posts as p2, $wpdb->term_relationships as tr, $wpdb->term_taxonomy as tt  ".
    "WHERE ".
    "((tr.term_taxonomy_id = $id AND ".
    "p1.ID = tr.object_id) OR ".
    "(tt.parent = $id AND ".
    "tr.term_taxonomy_id = tt.term_taxonomy_id AND ".
    "p1.ID = tr.object_id)) AND ".
    "p1.post_status = 'publish' AND ".
    "p2.post_parent = p1.ID AND ".
    "p2.post_mime_type LIKE 'image%'".
    "GROUP BY p2.ID".
    "<= 5". // you able to limit the db answer
    "", ARRAY_A );
print_r( $myrows );