public function before_update(Model $obj)
	{
		// If there are any relations loop through and check if any of them have been changed
		$relation_changed = false;
		foreach ( $this->_relations as $relation)
		{
			if ($this->relation_changed($obj, $relation))
			{
				$relation_changed = true;
				break;
			}
		}

		$objClassName = get_class($obj);
		$objProperties = $objClassName::properties();

		if ($obj->is_changed(array_keys($objProperties)) or $relation_changed)
		{
			$obj->{$this->_property} = $this->_mysql_timestamp ? \Date::time()->format('mysql') : \Date::time()->get_timestamp();
		}
	}