Question

I have a couple of actions to perform when saving a models, especially from the admin. I capitalize a couple of fields and check to make sure that either one field or the other is filled. I also create the field slug. RIght now these are split between overriding the clean and the save functions. It works now, but I am curious on when to use each. I looked through the docs, and I couldn’t find specifically which to use when.

Answer 1

You should use clean to do validation-related work, and to parse/change/otherwise clean the input. Capitalizing fields and generating a slug can happen here. I also use clean to force a field like post_type to a specific value in proxy models. If you raise django.core.exceptions.ValidationError('error text') inside clean, the 'error text' is added to the form.non_field_errors.

Save is the place to change the way a model is actually saved. For instance, I’ve used save to create a crop of an uploaded picture. ValidationErrors are not caught if raised here, and I feel like that’s the most important practical difference between the two.