/**
  * Delete location object by id.
  */
 public function delete()
 {
     if (isset($_GET['location_id'])) {
         $id = intval(wp_unslash($_GET['location_id']));
         $connection = WPGMP_Database::connect();
         $this->query = $connection->prepare("DELETE FROM {$this->table} WHERE {$this->unique}='%d'", $id);
         return WPGMP_Database::non_query($this->query, $connection);
     }
 }