Validate two fields in my fuel module
I have a little problem. I have a fuel module with two datetimes fields. The fields are: "date_start" and "date_end". I wish check that "date_end" is greater than or equal that "date_start". I think that I must do with the "on_before_validate" hook and add a validation with "add_validation", but I am trying but I can not do it. Can you help me please?