I am playing with a Django project which will deal with networking
information. I would like to enforce some additional constraints above
and beyond what the default Form fields provides.
For example, if I have a model to represent a 'subnet' it would have
both a network address (which I can save as an IPAddressField) and a
netmask which can be an IntegerField. I want to enforce that the host
portion of the address field is all zeros. This is pretty easy to
calculate given the address and netmask. But where should I put such
calcuations?
Class Subnet(models.Model):
address = models.IPAddressField()
netmask = models.IntegerField()
In reading the documentation I can find several places where it might
fit:
1) define a new custom Field subclass which incorporates both the
address and netmask as a single value. This would work, but I think I
might end up with a lot of extra new Field types and doesn't really
seem to be the right place.
2) override the 'save()' method on my Model subclass, and do the check
there. This seems pretty easy, but I'm not sure what to do if I fail
the validation. Raise ValidationError? Either way, this is the option
I'm leaning towards now.
3) catch the django.db.models.signals.pre_save signal. I haven't
played with signals though so I don't know how to set it up. I would
still have the question of what to do if I fail the validation.
4) Use the clean_address() method of a custom ModelForm. This is
pretty easy, and feels like it's sort of the right place because then
I can easily give the user a nice error message. On the other hand,
it's not really preventing the creation of invalid Subnet instances
via other methods (say via the Admin interface).
I'm sure other folks are dealing with the same issue. Where are you
doing this type of check?
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