Two Scoops of Django - Chapter 9: Best practices for Class-Based Views

1. Best practices
for
Class-Based Views
Two

2. Scoops

3. of

4. Django

5. -

6. Chapter

7. 9
@starwilly

8. Why Class-Based View

9. https://www.flickr.com/photos/kent-chen/8986036246
DRY
Don’t

10. Repeat

11. Yourself

12. Learning Curve

13. Django

14. Class-Based-View

15. Inspector
http://ccbv.co.uk/

16. Outline
• Django View
• Class-Based View (CBV)
• Generic Class-based View (GCBV)
• Detail View
• General Tips for Django CBVs

17. Django View
is simply a Python function that
takes a Web request and returns a Web response.
request View response

18. A Simple Function-Based View
from django.http import HttpResponse
def my_view(request):
if request.method == 'GET':
# view logic
return HttpResponse('result')
if request.method == 'POST':
# view logic
return HttpResponse('result')

19. Let’s Using
Class-based View

20. Class-Based View
django.views.generic.View
FBV CBV
def my_view(request):
from django.views.generic import View
class MyView(View):

21. request View response
def my_view(request):
…
return HttpResponse(‘result’)
from django.views.generic import View
class MyView(View):
request

22. ?
function

23. ?
response

24. ?
FBV CBV

25. django.views.generic.View

26. as_view()
Returns a callable view
that takes a request and returns a response

27. URLconf
urlpatterns = patterns(‘',
url(r'^$', ‘blog.views.homepage’),
)
from blog.views import HomepageView
urlpatterns = patterns(‘',
url(r'^$', HomepageView.as_view()),
)
FBV
CBV

28. Dispatch HTTP Verbs
from django.http import HttpResponse
def my_view(request):
if request.method == 'GET':
# view logic
return HttpResponse('result')
if request.method == 'POST':
# view logic
return HttpResponse('result')
from django.views.generic import View
from django.http import HttpResponse
class MyView(View):
?
?

29. dispatch()
def dispatch(self, request, *args, **kwargs):
# Try to dispatch to the right method;
# if a method doesn't exist, defer to the error handler.
# Also defer to the error handler if the
# request method isn't on the approved list.
if request.method.lower() in self.http_method_names:
handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
else:
handler = self.http_method_not_allowed
return handler(request, *args, **kwargs)

30. From FBV to CBV
FBV CBV
from django.http import HttpResponse
def my_view(request):
if request.method == 'GET':
# view logic
return HttpResponse('result')
if request.method == 'POST':
# view logic
return HttpResponse('result')
from django.views.generic import View
from django.http import HttpResponse
class MyView(View):
def get(self, request):
# view logic
return HttpResponse('result')
def post(self, request):
# view logic
return HttpResponse('result')

31. Generic Class-based views
(GCBVs)
CreateView
UpdateView
DetailView
DeleteView
ListView
TemplateView
RedirectView

32. Display A Blog Post (FBV v.s. CBV)
http://blog.mysite.com/post/12997/
FBV CBV
def post_detail(request, pk):
post = get_object_or_404(Post, pk=pk)
return render(request,
'post_detail.html',
{'post’: post})
class PostDetailView(DetailView):
model = Post

33. DetailView
Attributes
content_type = None
context_object_name = None
model = None
pk_url_kwarg = ‘pk'
queryset = None
slug_field = ‘slug'
slug_url_kwarg = ‘slug'
template_name = None
template_name_field = None
template_name_suffix = ‘_detail'
Method Flowchart
1 dispatch()
2 http_method_not_allowed()
3 get_template_names()
4 get_slug_field()
5 get_queryset()
6 get_object()
7 get_context_object_name()
8 get_context_data()
9 get()
10 render_to_response()

34. DetailView - get()
def get(self, request, *args, **kwargs):
self.object = self.get_object()
context = self.get_context_data(object=self.object)
return self.render_to_response(context)
as_view()
dispatch()
get()
get_object()
render_to_response() get_context_data()

35. DetailView
def post_detail(request, pk):
post = get_object_or_404(Post, pk=pk)
return render(request, ‘post_detail.html', {'post': post})
Method Flowchart
1 dispatch()
2 http_method_not_allowed()
3 get_template_names()
4 get_slug_field()
5 get_queryset()
6 get_object()
7 get_context_object_name()
8 get_context_data()
9 get()
10 render_to_response()
render_to_response()
get_object()
get_context_data()

36. How do you customize
CBVs behavior?

37. 1. Attributes

38. class PostDetailView(DetailView):
model = Post
context_object_name = 'post_obj'
template_name = 'post.html'
h1{{ object.title }}/h1
div
{{ object.content }}
/div
h1{{ post.title }}/h1
div
{{ post.content }}
/div
h1{{ post_obj.title }}/h1
div
{{ post_obj.content }}
/div
post.html
Customize - Attributes
post_detail.html

39. 2. Override methods

40. Customize - Overrides
class PostDetailView(DetailView):
model = Post
def get_queryset(self):
qs = super(PostDetail, self).get_queryset()
return qs.published()
def get_context_data(self, **kwargs):
context = super(PostDetail, self).get_context_data(**kwargs)
context[‘recommended_posts’] = (self.object.
get_recommended_post(user=self.request.user)[:5])
return context

41. 3. Mixins

42. class SecretMessageMixin(object):
def get_context_data(self,**kwargs):self).get_context_data(**kwargs)
context[“secret_message] = ‘Hello’
return context
class PostDetailView(SecretMessageMixin, DetailView):
model = Post
Customize - Mixins
{% extends ‘base.html’ %}
div
Secret Message is {{ secret_message }}
/div
views.py
post_detail.html

43. Mixins
1. Mixins should inherit from Python’s built-in object type
2. Base view by Django always go to the right
3. Mixins go to the left of the base view
class SecretMessageMixin(object):
…
class PostDetailView(SecretMessageMixin, DetailView):
model = Post
1
3 2

44. Tips for CBVs

45. Tip1. Access Control
from django.contrib.auth.decorators import login_required
class LoginRequiredMixin(object):
@classmethod
def as_view(cls, **initkwargs):
view = super(LoginRequiredMixin, cls).as_view(**initkwargs)
return login_required(view)
class PostDetail(LoginRequiredMixin, DetailView):
model = Post

46. MultiplePermissionsRequiredMixin
LoginRequiredMixin
PermissionRequiredMixin
CsrfExemptMixin
django-braces
https://github.com/brack3t/django-braces
FormValidMessageMixin
SuccessURLRedirectListMixin
FormInvalidMessageMixin
SelectRelatedMixin
JSONResponseMixin
AjaxResponseMixin

47. Tip2. Where should I put my code ?
dispatch()
get_context_data()
form_valid()
form_invalid()
get_queryset()
• Custom actions on every Http request
• Add additional object to context
• Custom Actions on Views with Valid Forms
• Custom Actions on Views with Invalid Forms
• Filter posts by query string

48. Custom Actions on Views with Valid Forms form_valid()
Custom Actions on Views with Invalid Forms form_invalid()
from django.views.generic import CreateView
from braces.views import LoginRequiredMixin
from .models import Post
class PostCreateView(LoginRequiredMixin, CreateView):
model = Post
fields = ('title', ‘content')
def form_invalid(self, form):
# Do custom logic
return super(PostCreateView, self).form_valid(form)
def form_valid(self, form):
# Do custom logic
return super(PostCreateView, self).form_valid(form)

49. Filter posts by query string get_queryset()
from django.views.generic import ListView
from .models import Post
class PostListView(ListView):
model = Post
def get_queryset(self):
queryset = super(PostListView, self).get_queryset()
q = self.request.GET.get('q')
if q:
queryset = qs.filter(title__icontains=q)
return queryset
{# templates/blog/_post_search.html #}
form action={% url “post-list %} method=GET
input type=text name=q/
button type=submitSearch/
/form

50. Tip3. Access url parameters
http://blog.mysite.com/author/john/
url(r’^author/(?Pusernamew+)/$’, AuthorPostListView.as_view())
from django.views.generic import ListView
from .models import Post
class AuthorPostListView.as_view(ListView):
model = Post
paginate_by = 10
def get_queryset(self):
user = get_object_or_404(User, username=self.kwargs['author'])
queryset = super(AuthorPostListView.as_view, self).get_queryset()
return queryset.filter(author=user)

51. Tip4. Using the View Object
class PostMixin(object):
@cached_property
def likes_and_favorites(self):
likes = self.objects.likes()
favorites = self.objects.favorites()
return {
'likes': likes,
'favorites': favorites,
'favorites_count': favorites.count(),
}
from django.utils.functional import cached_property
from django.views.generic import UpdateView
from .tasks import notify_users_who_favorited
class PostUpdateView(PostMixin, UpdateView):
model = Post
fields = ('title', 'content')
def form_valid(self, form):
notify_users_who_favorited(
instance=self.object,
favorites = self.like_and_favorites['favorites']
)

52. Tip4. Using the View Object
call

53. from

54. template
ContextMixin
def get_context_data(self, **kwargs):
if 'view' not in kwargs:
kwargs['view'] = self
return kwargs
{% extends 'base.html' %}
{% block likes_and_favorites %}
ul
liLikes: {{ view.likes_and_favorites.likes }}/li
liFavorites: {{ view.likes_and_favorites.favorites_count}} /li
/ul
{% endblock likes_and_favorites %}
class PostMixin(object):
@cached_property
def likes_and_favorites(self):
likes = self.objects.likes()
favorites = self.objects.favorites()
return {
'likes': likes,
'favorites': favorites,
'favorites_count': favorites.count(),
}
How

55. it

56. works

57. ?

58. Guidelines
• Less view code is better
• Never repeat code in views
• Views should handle presentation logic
• Keep your view simple
• Use FBV for 403, 404, 500 error handlers
• Keep your mixins simple

59. Summary
FBV v.s. CBV Generic Class-based View
as_view()
dispatch()
Generic Class-based View
Attribute
Method Override
Mixins
LoginRequiredMixin
Override Which Methods
Access url parameters
Using View Object
Customize CBVs Behavior
Tips for CBVs