public function getMidByKey( $post_id, $meta_key ) {

		/** @var \wpdb $wpdb */
		global $wpdb;
		$mid = $wpdb->get_var( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = %s LIMIT 1 ", $post_id, $meta_key ) );
		if ( ! empty( $mid ) ) {
			return absint( $mid );
		}

		return false;
	}