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URL-parameters and logic in Django class-based views (TemplateView)

Posted by: admin November 30, 2017 Leave a comment

Questions:

It is unclear to me how it is best to access URL-parameters in class-based-views in Django 1.5.

Consider the following:

View:

from django.views.generic.base import TemplateView


class Yearly(TemplateView):
    template_name = "calendars/yearly.html"

    current_year = datetime.datetime.now().year
    current_month = datetime.datetime.now().month

    def get_context_data(self, **kwargs):
        context = super(Yearly, self).get_context_data(**kwargs)
        context['current_year'] = self.current_year
        context['current_month'] = self.current_month
        return context

URLCONF:

from .views import Yearly


urlpatterns = patterns('',
    url(
        regex=r'^(?P<year>\d+)/$',
        view=Yearly.as_view(),
        name='yearly-view'
    ),
)

I want to access the year parameter in my view, so I can do logic like:

month_names = ["January", "February", "March", "April", "May", "June", "July",
               "August", "September", "October", "November", "December"]

     for month, month_name in enumerate(month_names, start=1):
        is_current = False
        if year == current_year and month == current_month:
            is_current = True
        months.append({
            'month': month,
            'name': month_name,
            'is_current': is_current})

How would one best access the url parameter in CBVs like the above that is subclassed of TemplateView and where should one ideally place the logic like this, eg. in a method?

Answers:

To access the url parameters in class based views, use self.args or self.kwargs so you would access it by doing self.kwargs['year']

Questions:
Answers:

In case you pass URL parameter like this:

http://<my_url>/?order_by=created

You can access it in class based view by using self.request.GET (its not presented in self.args nor in self.kwargs):

class MyClassBasedView(ObjectList):
    ...
    def get_queryset(self):
        order_by = self.request.GET.get('order_by') or '-created'
        qs = super(MyClassBasedView, self).get_queryset()
        return qs.order_by(order_by)

Questions:
Answers:

I found this elegant solution, and for django 1.5 or higher, as pointed out here:

Django’s generic class based views now automatically include a view
variable in the context. This variable points at your view object.

In your views.py:

from django.views.generic.base import TemplateView    

class Yearly(TemplateView):
    template_name = "calendars/yearly.html"
    # No here 
    current_year = datetime.datetime.now().year
    current_month = datetime.datetime.now().month

    # dispatch is called when the class instance loads
    def dispatch(self, request, *args, **kwargs):
        self.year = kwargs.get('year', "any_default")

    # other code

The dispatch solution found in this question.
As view is already passed within Template context, you don’t really need to care about it. In your template file yearly.html, it is possible to access those view attributes simply by:

{{ view.year }}
{{ view.current_year }}
{{ view.current_month }}

You can keep your urlconf as it is.

Good to mention that getting information into your template’s context overwrites the get_context_data(), so it is somehow breaking the django’s action bean flow.

Questions:
Answers:

So far I’ve only been able to access these url parameters from within the get_queryset method, although I’ve only tried it with a ListView not a TemplateView. I’ll use the url param to create an attribute on the object instance, then use that attribute in get_context_data to populate the context:

class Yearly(TemplateView):
    template_name = "calendars/yearly.html"

    current_year = datetime.datetime.now().year
    current_month = datetime.datetime.now().month

    def get_queryset(self):
        self.year = self.kwargs['year']
        queryset = super(Yearly, self).get_queryset()
        return queryset

    def get_context_data(self, **kwargs):
        context = super(Yearly, self).get_context_data(**kwargs)
        context['current_year'] = self.current_year
        context['current_month'] = self.current_month
        context['year'] = self.year
        return context