Question

I’d like to make sure that an integer field in my model never gets below a certain amount, is there a way to add some sort of constraint in Django? Or do I need to add a max() around all places I check for the value?

Answer 1

There are two ways:

• First one in form validation.

• The second one in the model validation (for the model forms).

updated

If you don’t use forms, then you can overwrite save() method or write code in pre-save signal:

pre_save.connect(yourModel_pre_save, sender = yourModel ) 

def yourModel_pre_save(sender, instance, **kwargs):
     if instance.some_value > some_other_value: 
         raise ValidationError('Value to high') 

don’t forget to enclose save() method into a try clause:

m = yourModel.objects.get( pk = 1 )
try:
    m.save()
except ValidationError, e:
        import itertools
        errors = list( itertools.chain( *e.message_dict.values() ) )

If you don’t like signals, then overwrite save method:

class yourModel(model.Model):
    description=models.CharField()
    some_value=models.IntegerField()
    ...

    def save(self, *args, **kwargs):
        if self.some_value > some_other_value: 
             raise ValidationError('Value to high') 
        super(yourModel, self).save(*args, **kwargs)