比较joomla控制器中的2个日期字段

i need to check 2 input form date fields in Joomla before saving a record and output a message to the user if the second date is greater than the first, without saving the record. I do not wish to do this check in JavaScript but in php. Also I do not wish to use the validate rules suggested by Joomla documentation. I want to do this in the sub-controller which handles the edit view. Can you please help?i need to check 2 input form date fields in Joo