protected function add_primary_keys_to_where($query)
	{
		$timestamp_start_name = static::temporal_property('start_column');
		$timestamp_end_name = static::temporal_property('end_column');

		$primary_key = array(
			'id',
			$timestamp_start_name,
			$timestamp_end_name,
		);

		foreach ($primary_key as $pk)
		{
			$query->where($pk, '=', $this->_original[$pk]);
		}
	}