nastyn8 nastyn8 - 7 months ago 354
Python Question

When to use get, get_queryset, get_context_data in Django?

I recently learned that you should override the get method when you specifically want to do something other than what the default view does:

class ExampleView(generic.ListView):
template_name = 'ppm/ppm.html'

def get(self, request):
manager = request.GET.get('manager', None)
if manager:
profiles_set = EmployeeProfile.objects.filter(manager=manager)
else:
profiles_set = EmployeeProfile.objects.all()
context = {
'profiles_set': profiles_set,
'title': 'Employee Profiles'
}


That's simple enough, but when should I use get_queryset or get_context_data over get? To me it seems like they basically do the same thing or am I just missing something? Can I use them together? This is a major source of confusion for me.

So to reiterate: In what cases would I use get over get_queryset or get_context_data and vise versa?

Answer

They indeed do different things.

get()

This is a top-level method, and there's one for each HTTP verb - get(), post(), patch(), etc. You would override it when you want to do something before a request is processed by the view, or after. But this is only called when a form view is loaded for the first time, not when the form is submitted. Basic example in the documentation. By default it will just render the configured template and return the HTML.

class MyView(TemplateView):
    # ... other methods

    def get(self, *args, **kwargs):
        print('Processing GET request')
        resp = super().get(*args, **kwargs)
        print('Finished processing GET request')
        return resp

get_query_set()

Used by ListViews - it determines the list of objects that you want to display. By default it will just give you all for the model you specify. By overriding this method you can extend or completely replace this logic. Django documentation on the subject.

class FilteredAuthorView(ListView):
    template_name = 'authors.html'
    model = Author

    def get_queryset(self):
        # original qs
        qs = super().get_queryset() 
        # filter by a variable captured from url, for example
        return qs.filter(name__startswith=self.kwargs.name)

get_context_data()

This method is used to populate a dictionary to use as the template context. For example, ListViews will populate the result from get_queryset() as author_list in the above example. You will probably be overriding this method most often to add things to display in your templates.

def get_context_data(self, **kwargs):
    data = super().get_context_data(**kwargs)
    data['page_title'] = 'Authors'
    return data

And then in your template you can reference these variables.

<h1>{{ page_title }}</h1>

<ul>
{% for author in author_list %}
    <li>{{ author.name }}</li>
{% endfor %}
</ul>

Now to answer your main question, the reason you have so many methods is to let you easily stick your custom logic with pin-point accuracy. It not only allows your code to be more readable and modular, but also more testable.

The documentation should explain everything. If still not enough, you may find the sources helpful as well. You'll see how everything is implemented with mixins which are only possible because everything is compartmentalized.

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