python - How to modify a Django model?

Question

If I would like to change e.g. Django's Site module:

from django.contrib.sites.models import Site

How would I do that in my project? Do I subclass or what do I do to change or add some code to it?

Or do I just create a new model?

Answer 1

You can add a field via inheritance

If you still need to keep a reference to the original Site object/row, you can use multi-table inheritance

from django.contrib.sites.models import Site

class MySite(Site):
    new_field = models.CharField(...)

    def new_method(self):
        # do something new

This allows you to have regular Site objects, that may be extended by your MySite model, in which case you can e.g. access the extra fields and methods through site.mysite, e.g. site.mysite.new_field.

Through model inheritance, you cannot alter an ancestor field

Through inheritance you cannot hide ancestor fields, because Django will raise a FieldError if you override any model field in any ancestor model.

And I wouldn't venture and write a custom DB migration for this, because then if you update Django, you may get schema conflicts with the Site model.

So here's what I would do if I wanted to store more info that the ancestor model allows:

class SiteLongName(Site):
    long_name = models.CharField(max_length=60)