I've created my own module for purchase rental and i want to put a constraints in Start Date and End Date. for exmaple, the user input an invalid Dates my created constraints pop up to warn the user that he/she inputs an invalid Date. How will I going to do that? and how will i call my def function in the save button?? here my codes in creating my def:

    def _validate_date(self,cr,uid,ids,context=None):

       for line in self.browse(cr,uid,ids,context=context):

           netsvc.Logger().notifyChannel("NETSV NETSV NETSV NETSV NETSV NETSV NETSV NETSV START DATE", netsvc.LOG_INFO, ' '+str(line.start_date))

           netsvc.Logger().notifyChannel("NETSV NETSV NETSV NETSV NETSV NETSV NETSV NETSV ENDSS DATE", netsvc.LOG_INFO, ' '+str(line.end_date))

           if line.start_date and not line.end_date:

               raise orm.except_orm(

                   _('Error:'),

                   _("Missing End Date for purchase order line with"

                       "Description '%s'.")

                   % (line.name))

           if line.end_date and not line.start_date:

               raise orm.except_orm(

                   _('Error:'),

                   _("Missing Start Date for purchase order line with"

                        "Description '%s'.")

                   % (line.name))

           if line.end_date and line.start_date and \

                   line.start_date > line.end_date:

               raise orm.except_orm(

                   _('Error:'),

                   _("Start Date should be before or be the same as "

                       "End Date for purchase order line with Description '%s'.")

                   % (line.name))

       return True

   

   _constraints = [

       (_validate_date, "Error msg in raise",

            ['start_date','end_date','product_id']),

       ]