Django ModelForm: What is save(commit=False) used for?

Question

Why would I ever use save(commit=False) instead of just creating a form object from the ModelForm subclass and running is_valid() to validate both the form and model?

In other words, what is save(commit=False) for?

If you don't mind, could you guys provide hypothetical situations where this might be useful?

Answer 1

That's useful when you get most of your model data from a form, but you need to populate some null=False fields with non-form data.

Saving with commit=False gets you a model object, then you can add your extra data and save it.

This is a good example of that situation.

Answer 2

Here it is the answer (from docs):

# Create a form instance with POST data. >>> f = AuthorForm(request.POST)  # Create, but don't save the new author instance. >>> new_author = f.save(commit=False) 

The most common situation is to get the instance from form but only 'in memory', not in database. Before save it you want to make some changes:

# Modify the author in some way. >>> new_author.some_field = 'some_value'  # Save the new instance. >>> new_author.save()