Decorators for class-based views that use class variables in Django

Question

I have a class-based view that is inherited by other views:

class EditProfileAttribute(View):
    template_name = 'mytemplate.html'
    ThisModel = models.Model
    def get(request, model_id):
        instance = self.ThisModel.objects.get(id=model_id)
        if instance.user != request.user:
            return HttpResponseForbidden("Forbidden.")
        # add form here
        return render(request, self.template_name, {'model_id':model_id})

    def post(request, model_id):
        instance = self.ThisModel.objects.get(id=model_id)
         if instance.user != request.user:
             return HttpResponseForbidden("Forbidden.")
         # do some editing here, save forms, etc.
         return HttpResponse("Edited")

class EditAddressView(EditProfileAttributeView):
        ThisModel = Address

class EditLinkView(EditProfileAttributeView):
        ThisModel = Link

Now in my models.py file:

class Address(models.Model):
    user = models.ForeignKey(User)
    address = models.TextField(max_length=100)

class Link(models.Model):
    from_user = models.ForeignKey(User, related_name='from_link')
    to_user = models.ForeignKey(User, related_name='to_link')

The class EditAddressView works because the User field is explicitly called user, but the class EditLinkView does not because it requires instance.from_user instead of instance.user. (Let's just say I can't rename from_user).

What I'd like to do is to transform the instance.user != request.user part into a decorator where the syntax user is not required, but I can't figure out how to reference self.ThisModel.

At the same time, this allows me not to repeat the same method for both get and post.

Is what I want even possible?

Alasdair · Accepted Answer · 2016-11-02 13:16:00Z

3

You can use another class attribute to store the name of the user field, and then use get_attr to fetch the value in the method.

If you want to avoid duplicating code in get and post, then factor the common code into a helper method, or override dispatch instead.

class EditProfileAttribute(View):
    ThisModel = models.Model
    user_field_name = 'user'

    def dispatch(self, request, *args, **kwargs):
         self.instance = self.ThisModel.objects.get(id=kwargs['model_id'])
         if getattr(self.instance, self.user_field_name) != request.user:
             return HttpResponseForbidden("Forbidden.")
         # calling super() will call get() or post() as appropriate
         return super(EditProfileAttribute, self).dispatch(request, *args, **kwargs)

edited Nov 2, 2016 at 13:16

answered Nov 2, 2016 at 13:00

Alasdair

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3 Comments

irene Over a year ago

Thanks @Alasdair! That solves my first problem -- but I have another one. What if I have a POST method that requires the same instance check? Is there really no way around having to copy the same line in both the get() and post() methods?

irene Over a year ago

Also, what if I have a DeleteView that also requires a similar check? It would help much if I don't have to copy the same lines over and over again...

Alasdair Over a year ago

You can override the dispatch method to avoid duplicating code in get() and post(). The code above should work as a mixin, I can't see why your DeleteView can't inherit it.

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