Get an array containing ONLY post IDs of attached images

Question

I am in need of putting an array of all images attached to a post into a custom field so that I can display they on the fly using my template's existing functions.

I have gotten this real close and am successfully able to set the value of the custom meta field _et_used_images with the contents of the array returned by get_children, I just need some assistance getting the values returned from get_children converted/sanitized to only include the post ID of the image and not the entire image object as I am getting now:

Here is the code I am using. I have tried using a foreach loop to add to a $get_children_array[] but I am missing something and just reverted back to where it was working, but returning ALL info instead of just postID. (Example of array returned at end).

            if ( 'thumbnail' == $column_name ) {
            // thumbnail of WP 2.9
            $thumbnail_id = get_post_meta( $post_id, '_thumbnail_id', true );
            // image from gallery
            $attachments = get_children( array('post_parent' => $post_id, 'post_type' => 'attachment', 'post_mime_type' => 'image') );

            if ($thumbnail_id)
                $thumb = wp_get_attachment_image( $thumbnail_id, array($width, $height), true );
            elseif ($attachments) {
        //Set value of et_images via attached posts.


                foreach ( $attachments as $attachment_id => $attachment ) {
                    $thumb = wp_get_attachment_image( $attachment_id, array($width, $height), true );
                }

            }
                if ( isset($thumb) && $thumb ) {
                    echo $thumb;
                //update_post_meta($post_id, '_thumbnail_id', $attachment_id); //Uncomment to generate thumbnails from attached media.
                update_post_meta($post_id, '_et_used_images', $attachments); 


                } else {
                    echo __('None');
                }
        }
}

EXAMPLE OF RETURNED ARRAY:

a:18:{i:897;O:7:"WP_Post":24:{s:2:"ID";i:897;s:11:"post_author";s:1:"3";s:9:"post_date";s:19:"2011-08-12 05:53:33";s:13:"post_date_gmt";s:19:"2011-08-12 05:53:33";s:12:"post_content";s:153:"A grand home located in Point Loma required a grand landscaping to complement the site. this was achieved with the site planting and landscape features. ";s:10:"post_title";s:33:"1-landscape-design-point-loma-job";s:12:"post_excerpt";s:0:"";s:11:"post_status";s:7:"inherit";s:14:"comment_status";s:4:"open";s:11:"ping_status";s:4:"open";s:13:"post_password";s:0:"";s:9:"post_name";s:35:"1-landscape-design-point-loma-job-3";s:7:"to_ping";s:0:"";s:6:"pinged";s:0:"";s:13:"post_modified";s:19:"2011-08-12 05:53:33";s:17:"post_modified_gmt";s:19:"2011-08-12 05:53:33";s:21:"post_content_filtered";s:0:"";s:11:"post_parent";i:713;s:4:"guid";s:95:"http://example.website.com/wp-content/uploads/2011/07/1-landscape-design-point-loma-job1.jpg";s:10:"menu_order";i:2;s:9:"post_type";s:10:"attachment";s:14:"post_mime_type";s:10:"image/jpeg";s:13:"comment_count";s:1:"0";s:6:"filter";s:3:"raw";}i:896;O:7:}}

Answer 1

The following code should work for you,

$images = get_children( array('post_parent' => $post_id, 'post_type' => 'attachment', 'post_mime_type' => 'image') );
$image_ids = array();
if($images){
   foreach( $images as $imageID => $imagePost ){
      array_push($image_ids, $imageID);
   }
}

The array $image_ids would get you the image IDs.

Answer 2

You can make use of the fields parameter with the value ids to get just those. You can use it with get_children(), which basically works like or is a wrapper for get_posts(), which again is wrapper for WP_Query. So you can do:

// this:
$children_images_ids = get_children(
    array(
        'post_parent'    => get_the_ID(),
        'post_status'    => 'inherit',
        'post_type'      => 'attachment',
        'post_mime_type' => 'image',
        'fields'         => 'ids'
    )
);

// or this:
$children_images_ids = get_posts(
    array(
        'post_parent'    => get_the_ID(),
        'post_status'    => 'inherit',
        'post_type'      => 'attachment',
        'post_mime_type' => 'image',
        'fields'         => 'ids'
    )
);

// or this:
$children_images_obj = new WP_Query(
    array(
        'post_parent'    => get_the_ID(),
        'post_status'    => 'inherit',
        'post_type'      => 'attachment',
        'post_mime_type' => 'image',
        'fields'         => 'ids'
    )
);
$children_images_ids = $children_images_obj->posts;

In any of those cases $children_images_ids will already be an array of IDs looking for example somewhat like this:

Array
(
    [0] => 123
    [1] => 456
    [2] => 789
)

Answer 3

OK, so I ended up going a completely different route with this and have a nice working solution

function update_images_meta( $object_id ) {
    // Get the post using its ID
    $post = get_post( $object_id );

    // determine if we are dealing with a post (a parent) or an attachment (a child)
    switch( $post->post_type ){
        case 'attachment':
            $post_id = $post->parent;
            break;

        default:
            $post_id = $post->ID;
            break;
    }

    if($post_id) {
        // Get all the image attachments for the post
        $param = array(
                'post_parent'       => $post_id, 
                'post_type'         => 'attachment', 
                'post_mime_type'    => 'image'
        );

        $attachments = get_children(  $param );

        // Initialize the array
        $atts = array();

        // Fill the array with attachment ID's
        foreach($attachments as $attachment)
            $atts[] = $attachment->ID;

        // Disable this hook which was overwrinting our changes
        remove_action( 'save_post', 'flexible_save_details', 10 );

        // Update the post's meta field with the attachment arrays
        update_post_meta( $post_id, '_et_used_images', $atts );

    }
}