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Django Tips #15 Using Mixins With Class-Based Views

Django Tips #15 Using Mixins With Class-Based Views

I was reading today the book Two Scoops of Django (affiliate link) by Audrey and Daniel Roy Greenfeld and found some interesting tips about using class-based views with mixins.

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Some general rules to use mixins to compose your own view classes, as suggested by Kenneth Love, which I grabbed from the above mentioned book:

  1. The base view classes provided by Django always go to the right;
  2. Mixins go to the left of the base view;
  3. Mixins should inherit from Python’s built-in object type

Following an example to illustrate the rules:

class FormMessageMixin(object):
    @property
    def form_valid_message(self):
        return NotImplemented

    form_invalid_message = 'Please correct the errors below.'

    def form_valid(self, form):
        messages.success(self.request, self.form_valid_message)
        return super(FormMessageMixin, self).form_valid(form)

    def form_invalid(self, form):
        messages.error(self.request, self.form_invalid_message)
        return super(FormMessageMixin, self).form_invalid(form)


class DocumentCreateView(FormMessageMixin, CreateView):
    model = Document
    fields = ('name', 'file')
    success_url = reverse_lazy('documents')
    form_valid_message = 'The document was successfully created!'

In a similar way you could reuse the same FormMessageMixin in a UpdateView for example, and also override the default form_invalid_message:

class DocumentUpdateView(FormMessageMixin, UpdateView):
    model = Document
    fields = ('name', )
    success_url = reverse_lazy('documents')
    form_valid_message = 'The document was successfully updated!'
    form_invalid_message = 'There are some errors in the form below.'

Since Django 1.9 we have the built-in mixins LoginRequiredMixin and UserPassesTestMixin. If you are using them in your view classes, they should always go on the far left side, like below:

class DocumentUpdateView(LoginRequiredMixin, FormMessageMixin, UpdateView):
    model = Document
    fields = ('name', )
    success_url = reverse_lazy('documents')
    form_valid_message = 'The document was successfully updated!'


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