Delete child post and attachment links to parent post

Question

I have a hierarchical posts, when ever I delete the child posts its attachments go and link to deleted post's parent

How can I stop this?

Answer 1

There's no way of doing this without "listening" for the responsible database query and altering it with the query filter, thanks to this line in wp_delete_post():

// Point all attachments to this post up one level
$wpdb->update( $wpdb->posts, $parent_data, $parent_where + array( 'post_type' => 'attachment' ) );

The following will override the query and set the post parent back to 0 (as opposed to inheriting the deleted items parent):

/**
 * Remove the parent fallback for attachments of children when they are
 * deleted.
 *
 * @link http://wordpress.stackexchange.com/q/142916/1685
 */
class WPSE_142916_Remove_Parent_Fallback {
    public static function init( $post_id ) {
        new self( $post_id );
    }

    public function __construct( $post_id ) {
        $this->post_parent = wp_get_post_parent_id( $post_id );
        $this->post_id = $post_id;

        add_action( 'delete_post', array( $this, 'un_hook' ) );
        add_filter( 'query',       array( $this, 'replace' ) );
    }

    public function replace( $query ) {
        global $wpdb;

        if ( $query === "UPDATE `$wpdb->posts` SET `post_parent` = $this->post_parent WHERE `post_parent` = $this->post_id AND `post_type` = 'attachment'" ) {
            $query = str_replace( "`post_parent` = $this->post_parent", '`post_parent` = 0', $query );
        }

        return $query;
    }

    public function un_hook() {
        remove_action( 'delete_post', array( $this, 'un_hook' ) );
        remove_filter( 'query',       array( $this, 'replace' ) );
    }
}

add_action( 'before_delete_post', array( 'WPSE_142916_Remove_Parent_Fallback', 'init' ) );