ModelForm's 'initial' attribute unexpectedly persists across different instances

[Haisheng HU]

There are two UpdateView's (or CreateView's) A and B with their corresponding ModelForm A and B. From UpdateView A the 'initial' attribute in ModelForm A was set to a certain value. After this, UpdateView B and ModelForm B were created. Now the 'initial' attribute in ModelForm B was not {}, but the same as ModelForm A.

class UpdateViewA(UpdateView):
    model = Project
    form_class = ProjectFormA
    ...
    def get_form_kwargs(self, **kwargs):
        kwargs = super(UpdateViewA, self).get_form_kwargs(**kwargs)
        if self.get_object().kickoff_date == None:
            kwargs['initial']['kickoff_date'] = datetime.date.today()
        return kwargs

class UpdateViewB(UpdateView):
    model = Project
    form_class = ProjectFormB
    ...

class ProjectFormA(ModelForm):
    ...
    class Meta:
        model = Project

class ProjectFormB(ModelForm):
    ...
    class Meta:
        model = Project

[Aymeric Augustin]

One could expect that the accessor get_initial() return an object value that can be safely mutated. Your patch achieves this.

The alternative is to forbid mutating the result of get_initial() in the documentation. You would have to override get_initial() instead of get_form_kwargs().

    def get_initial(self):
        result = {}
        if self.get_object().kickoff_date == None:
            result['kickoff_date'] = datetime.date.today()
        result.update(super(..., self).get_initial())
        return result

I'm not sufficiently familiar with the generic view to make a decision here, but either the code or the docs must be improved.

[Haisheng HU]

The alternative solution raised by @aaugustin is feasible, although it's not so straightforward to construct a local dict and update it with a super class method.

Some people adopted the get_form_kwargs way:
​http://stackoverflow.com/questions/4512254/user-current-user-on-new-django-class-views-forms

Just my 2 cents.

[Gabriel Hurley]

get_initial shouldn't return an object that's unsafe to mutate, and I can't see a compelling reason for it to return an immutable object. The greatest flexibility would be afforded by a method as in the patch since it allows you to alter self.initial if you so desire, but also prevents the gotcha case of accidentally mutating the initial data for the entire process.

This patch still needs a test case, and a note in the documentation would also be helpful.

[Aymeric Augustin]

#16701 was a duplicate.

[wilfred@…]

Test case to ensure get_initial() returns a fresh dict

[Jacob]

Milestone 1.4 deleted

[wilfred@…]

documenting behaviour change in the docs

[wilfred@…]

Documentation added. I've stated '1.4' in my docs patch, although I was unsure. Should it say 'trunk' instead?

[Claude Paroz]

#17759 was a duplicate (ans has a patch, too).

[Claude Paroz]

Consolidate fix/test/docs patches

[Claude Paroz]

In [17765]:

Fixed #16138 -- Made FormMixin get_initial return a copy of the 'initial' class variable. Thanks hanson2010, wilfred@… and agriffis for their work on the patch.