View mixins

Mixins are the essence of DRY code in class-based views. Like model mixins, a view mixin takes advantage of Python's multiple inheritance to easily reuse chunks of functionality. They are often parent-less classes in Python 3 (or derived from object in Python 2 since they are new-style classes).

Mixins intercept the processing of views at well-defined places. For example, most generic views use get_context_data to set the context dictionary. A derived class or mixin can insert an additional context variable, such as feed that contains a user's feed of posts. Here is how that mixin would look like:

class FeedMixin: 
    def get_context_data(self, **kwargs): 
        context = super().get_context_data(**kwargs) 
        context["feed"] = models.Post.objects.viewable_posts(
            self.request.user) 
        return context 

The get_context_data method first populates the context by calling its namesake in all the base classes. Next, it updates the context dictionary with the feed...