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 v

Answer 1

As a "real example", consider a user model where the email address and the username are always the same, and then you could overwrite your ModelForm's save method like:

class UserForm(forms.ModelForm):
    ...
    def save(self):
        # Sets username to email before saving
        user = super(UserForm, self).save(commit=False)
        user.username = user.email
        user.save()
        return user

If you didn't use commit=False to set the username to the email address, you'd either have to modify the user model's save method, or save the user object twice (which duplicates an expensive database operation.)