List most recent image uploads, but only for specific custom post type

Question

I can get a list of the most recent image attachments like so:

$attachments = get_posts( array(
    'post_type' => 'attachment',
    'posts_per_page' => $number,
    'post_mime_type' => 'image'
) );

This returns all images that have been recently uploaded, whether they are attached to a post or page, or unattached through the Media menu.

What I'd like is to limit that list to only images that are attached to a custom post type I've created. (The custom post type is not that important; the same question could be: 'only images attached to Posts' or 'only images attached to Pages.')

I realize I could test each image after running the above query and eliminate any whose parent is not the right post type, but I want to return a specific number of images ($number), and this method could eliminate some or all of the returned images!

Answer 1

Did you try adding a filter to get_posts. This isn't tested, just a thought after a bit of searching :

 function my_filter( $query )
 {
      if( is_home() ) //Example, if u want to display recent images on home
      {
           $query->set( 'post_type', array( 'attachment', 'my_cpt' ) );
      }
 }
 add_filter( 'pre_get_posts', 'my_filter' );

EDIT : After rereading, I don't think it accomplishes what you're trying to do, I think it will display both attachments, and posts of your CPT.

Guess i'ill leave it here in case it gives you any ideas.

EDIT 2: The only other way besides filtering in PHP that I can think of would be a custom sql query, and then setting up the post data. EX :

$sql = "SELECT * FROM wp_posts
        WHERE post_type = 'attachment'
        AND post_parent IN (SELECT ID FROM wp_posts WHERE post_type = 'your-cpt')
        //ORDER BY";

 $posts = $wpdb->get_results( $sql, OBJECT );

 //loop - setup_postdata

More info: Wordpress Codex

Answer 2

First you get the recent modified posts for your CPT only. Then get their attachments. Off course you can have some logic to limit array of attachments.

$mycpt = get_posts(array(
                 'post_type'=>'mycpt',
                  'posts_per_page'=>-1,
                  'orderby'=>'modified'
                 ));

$attachments = array();
foreach($mycpt as $mycpt)
{
  $post_attachements = get_posts( array(
    'post_parent'       => $mycpt->ID,
    'post_type'         => 'attachment',
    'post_mime_type'    => 'image',   
    'posts_per_page'    => -1
) );
   foreach($post_attachements as $post_attachements){
     $attachments[] = $post_attachements;
    }

}

Answer 3

put this code within the loop in single custom post type

$attachments = get_posts( array(
    'post_parent'       => get_the_ID(),
    'post_type'         => 'attachment',
    'post_mime_type'    => 'image',
    'orderby'           => 'menu_order',
    'order'             => 'DESC',
    'posts_per_page'    => -1
) );

if ( $attachments ) {
    foreach ( $attachments as $attachment ) {
        $attID     = $attachment->ID;
        echo '<a href="'.wp_get_attachment_url( $attID ).'" alt="'.apply_filters( 'the_title', $attachment->post_title ).'" class="att-item">'.wp_get_attachment_image( $attID, 'thumbnail' ).'</a>';
    }
}