2019-04-24 Django

Django Class Based Views

Django Class Based Views

Remember that things with similar functionality and only slight differences can be reused by the use of classes in python, well we can do the same with django views.

• class View

• classgenericViews - built on view

  from django.views.generic import view

Have the class extend View

class HelloWorldView(View):
    def get(self, request):
        return HttpResponse("Hello World!")

Create a get method that takes self because it is an instance and request just like function based views

The url is a bit different as it must point to a callable (function) not a class

So we use class.as_view() which handles instanitating class

url(r'^hello/$', views.HelloWorldView.as_view(), name='hello')

as_view() is a class method so it does not need an instance of a class to run, it creates the instance. Like setting up request and then runs dispatch method which runs the HTTP methods get

TemplateView

There is also a TemplateView class

from django.views.generic import View, TemplateView

class HomeView(TemplateView): template_name = ‘home.html’

Override context data

class NameView(TemplateView):
    template_name = 'name.html'

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['name'] = 'hello'
        return context

DetailView and ListView

Using defaults saves time

from django.views.generic import ListView, DetailView

class TeamListView(ListView):
    model = models.Team
    context_object_name = 'teams'

class TeamDetailView(DetailView):
    model = models.Team

Sticking with the defaults - speeds you up

CreateView, UpdateView, DeleteView

from django.views.generic import (
    ListView, DetailView,
    CreateView, UpdateView, DeleteView
)

Need to define model and fields for CreateView Also add a get_absolute_url method to the model

Reverse Lazy

from django.core.urlresolvers import reverse_lazy

So reverse lazy is ealuated when view is instantiated not when file is created If view does not exist it does not matter

Override queryset

You can set queryset variable in a class based view, but queryset is mutable so you must write .all() at end to get a fresh one

Best way is to override get_query_set method

So you can for example only delete a team if you are a superuser

def get_queryset(self):
    if not self.request.user.is_superuser:
        return self.model.objects.filter(coach=self.request.user)
    return self.model.objects.all()

You can also change the intial data:

def get_initial(self):
    intial = super().get_initial()
    initial['coach'] = self.request.user.pk
    return initial

An Excellent resource to use to know the method is CCBV

Combining class-based views

Example extending from both: DetailView, UpdateView

class TeamDetailView(DetailView, UpdateView):
    model = models.Team
    fields = ('name', 'practice_location', 'coach')
    template_name = "teams/team_detail.html"

You should explicitly set template_name when combining, so django knows what is the template to use. Otherwise I think it takes the first.

Problem that sometimes happen is that the super() methods work left to right. So the left class being extended is run first then right class.

CreateView looks for a object and ListView only has multiple objects.

Sometimes you can just reverse the order

Mixins

Sometimes you need to override or manipulate a class

But to do it in many locations use a little repeatable class: Mixins

check ccbv.co.za for docs on class based views and mixins

To enforce authentication use the loginRequiredMixin

from django.contrib.auth. import LoginRequiredMixin

Then inherit from in a class based view on the left:

class TeamCreateView(LoginRequiredMixin, CreateView):
    ...

Then it will automatically redirect to the accounts/login page

Read the Mixins in Class based views docs

Django Braces

Creating a Custom Mixin

Create a file called mixins.py

Create the mixin class:

class PageTitleMixin:
    page_title = ""

    def get_pagetitle(self):
        return self.page_title

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["page_title"] = self.get_pagetitle
        return context

Import it:

from . import mixins

Extend from the mixin:

class TeamCreateView(mixins.PageTitleMixin, CreateView):
    page_title = "Create a new team"

    def get_pagetitle(self):
        obj = self.get_object()
        return "Update {}".format(obj.name)

Now you can set the page_title in the class based view