Add validate_unique flag to ModelForm.Meta

[Greg Wogan-Browne]

ModelForm's currently have a wart in that if you override clean()
you have to call super() to ensure that unique constraints are validated.

This can lead to surprises if you haven't read the documentation closely.

It seems to me this would be better as a property on the Meta class.

Example:

    class DontCheckForm(ModelForm):
        def clean(self):
	    return self.cleaned_data
	class Meta:
	    model = SomeModel

Becomes:

    class DontCheckForm(ModelForm):
        class Meta:
	    model = SomeModel
	    validate_unique = False

[Greg Wogan-Browne]

Outline of suggested approach

[Russell Keith-Magee]

I don't see how adding a new option is a fix for "user needs to read the documentation" -- any new option will also require documentation, and that documentation will need to be read and understood.

If you override a method, you need to call super() to get the superclass' behavior. This is entirely consistent Python idiom. The default implementation of clean() validates all the uniqueness conditions for the model. If you implement clean(), and don't call super(), then you don't get that validation. I don't see the value in adding an option flag to implement behavior.

If your argument is that documentation needs to be improved around the implications of calling super(), then I'm happy to entertain suggestions.