Handling objects.populate(True) in a ModelForm

[benjaoming]

Please consider including this tip in the docs as it's quite crucial to make auto-population work in ModelForms - a model form does not create new instances through objects.create, rather it calls the constructor. Thus, the save method would have to explicitly call objects.populate(True).create() to get auto population. I achieve this in the save method. It may not be a drop-in replacement since someone may modify form.instance before calling the save() method, which definitely breaks this design.

Thanks :)

def save(self, *args, **kwargs):
    if not self.instance.pk:
        extra_fields = kwargs.pop('extra_fields', {})
        fields = extra_fields
        fields.update({k: self.cleaned_data[k] for k in self._meta.fields})
        self.instance = self._meta.model.objects.populate(True).create(
            **fields
        )
    return super(CreateEventForm, self).save(*args, **kwargs)

[zlorf]

Well, instance constructor behaves exactly the same as objects.create in terms of auto-population and field name rewriting. So to do this in easy way:

from modelstranslation.utils import auto_populate

def save(self, *args, **kwargs):
    with auto_populate():
        return super(CreateEventForm, self).save(*args, **kwargs)

or one can even set MODELTRANSLATION_AUTO_POPULATE.

[benjaoming]

I tried both the context decorator and the global setting, none of them worked.

[benjaoming]

The model instance constructor does not invoke the model manager AFAIK. Or well, my empirical results confirm this.

[zlorf]

Yes, I does not invoke model manager. But auto-population actually takes place in model constructor: https://github.com/deschler/django-modeltranslation/blob/master/modeltranslation/translator.py#L152 and manager's create only wraps inner call (which, in turns, call object constructor) inside auto_populate context manager: https://github.com/deschler/django-modeltranslation/blob/master/modeltranslation/manager.py#L202

[benjaoming]

I've tested it on a ModelForm instance, the auto_populate decorator does not work. Global setting does not work.

BUT! I get the problem now!! :)

Yes, patch_constructor is called correctly. Problem is, that after invoking the constructor (in ModelForm.__init__), the ModelForm will then set the field values from cleaned_data (ModelForm.save). This part is not auto_populated. Hence, we need a ModelForm that creates the new instance with a method that is caught by the populator.

[benjaoming]

Btw thanks for the pointers, it's nice to see modeltranslation under the hood. It's solid work, I really enjoy using it!!

[ghost]

@benjaoming I have the same problem. Did you solve it? Can you explain your solution? Thanks!

[benjaoming]

@sabriinfo the work-around for a ModelForm instance is given in the original first post :)

You can use a similar method if you find that other things are not caught by the auto population.