[Answered ]-Limit Django ModelForm ForeignKey choices depending on request.user

I do this by overriding CreateView.get_form_class() in order to modify the attributes of the relevant field of the form before it is passed to the rest of the view.

The default method, inherited from views.generic.edit.ModelFormMixin, returns a ModelForm that represents all the editable fields of the model in the base_fields dictionary. So it’s a good place to make any desired changes and also has access to self.request.user.

So for the above example, in views.py we might say:

class ContentCreateView(LoginRequiredMixin, CreateView):
    model = Content
    fields = '__all__'

    def get_form_class(self):
        modelform = super().get_form_class()
        modelform.base_fields['folder'].limit_choices_to = {'user': self.request.user}
        return modelform

Read more about ForeignKey.limit_choices_to in the docs.

Note that field choices are enforced by form validation so this should be quite robust.

The following mixin looks automatically limits the choices for all foreign key fields that point to a model that has a user field:

class LimitForeignKeyChoicesToSameUserMixin:

    def get_form_class(self):
        this_model_has_user_field = False
        choice_limited_fields = []
        for field in self.model._meta.get_fields():
            if isinstance(field, ForeignKey) or isinstance(field, ManyToManyField):
                if field.name == 'user':
                    this_model_has_user_field = True
                elif hasattr(field.related_model, 'user'):
                    choice_limited_fields.append(field.name)
        form_class = super().get_form_class()
        if this_model_has_user_field:
            for field in choice_limited_fields:
                form_class.base_fields[field].limit_choices_to = {'user': self.request.user}
        return form_class  

And then I use the following base class for all ‘add’ views:

class AddViewBase(LoginRequiredMixin, LimitForeignKeyChoicesToSameUserMixin, 
                  CreateView, FormMixin):
    slug_url_kwarg = 'id'
    slug_field = 'id'

    def form_valid(self, form):
        form.instance.user = self.request.user
        return super().form_valid(form)

And this base class for ‘edit’ views:

class EditViewBase(LoginRequiredMixin, LimitForeignKeyChoicesToSameUserMixin,
                   UpdateView):
    slug_url_kwarg = 'id'
    slug_field = 'id'