I have setup a custom meta_key for attachments. Since it is a radio button with Yes/No options, and the default value is always Yes, I need that this default value is saved into the db when the attachment is created.
Right now the problem is that when I upload an image, the Edit Media page shows me that the value for this meta_key is "Yes", but it is actually not saved in the database until I click "Save All Changes" or "Update Media".
Since these attachments can be added both by manually uploading files and automatically by importing an RSS feed, I need the default value to be created at the moment the attachment is created in the db.
UPDATE: To explain the issue in more detail, this is the code I am using in the template to find the attachments. I don't know if I can modify this to also query the attachments when the _show_attach is null?
$attached_photos = get_children(array( 'post_parent' => get_the_ID(), 'post_type' => 'attachment', 'numberposts' => -1, // show all 'post_status' => null, 'post_mime_type' => 'image', 'order' => 'ASC', 'orderby' => 'menu_order', 'meta_key' => '_show_attach', 'meta_value' => 'false', 'meta_compare' => '!=' ));