BaseModelForm.is_valid() should document how it modifies the BaseModelForm.instance

[Danang Rahmatullah]

BasedModelForm extends BaseForm. When BaseModelForm().is_valid() is called, its super is called which in turn calls BaseForm.errors (property method). The issue is when there are no errors (self._errors is None): BaseForm calls full_clean() which runs the _post_clean() hook defined in BaseModelForm, finally modifying BaseModelForm.instance.

Given the abstraction level of subclasses of BaseModelForm such as forms.ModelForm, it is very unreasonable to expect that a seemingly simple function like is_valid() to create such a big change to a property as important as instance. I hope this side-effect is clearly explained in the documentation or have the code refactored to separate the modifying effect of is_valid() function from the form validity check

# form.instance.myfield = False
form = MyModelForm(instance=myinstance, data={"myfield": True})
# form.instance.myfield = False
form.is_valid()
# form.instance.myfield = True

[Mariusz Felisiak]

I hope this side-effect is clearly explained in the documentation or have the code refactored to separate the modifying effect of is_valid() function from the form validity check

Yes, this is explained in detail in ​docs. I'm not sure what change you're proposing.

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[Danang Rahmatullah]

Thanks for the link attached. I was mainly looking at the ​Forms API page which currently has no references to the link you have posted. In that case, I think adding a small reference link to the ​validation page from the forms API page would greatly help others.