Class Based Views - Past, Present and Future

One of the big changes in Django 1.3 was the introduction of Class-Based Views. Opinion on them is strongly divided; some love them, some hate them.

In this talk, we'll look at the history that led to the development of Class-Based Views, and the current state of play. We'll look at some interesting design patterns that are possible by exploiting the features of Class-Based views. And we'll look to what the future could hold for Django's Class-based future.

Transcript

1. Class Based Views:
   Past, Present and Future Dr Russell Keith-Magee DjangoCon AU 2014
4. Class Based Views
5. In the beginning...
6. In the beginning... • It’s 2005 • Django is for building websites • Views are for displaying content • There a lots of common patterns in views • We all like being DRY
8. Generic Views • Display a template • Display a single object • Display a list of objects • Display a form • Create, Update, Delete • Display a date archive
9. Key features • Each view is a function • Configuration via arguments
10. Example: Before def edit_book(request, book_id):! try:! book = Book.objects.get(pk=book_id)! except Book.DoesNotExist:! raise Http404! if request.method == 'POST':! form = BookForm(! instance=book, ! data=request.POST)! if form.is_valid():! form.save()! return HttpResponseRedirect(! book.get_absolute_url())! ...
11. Example: Before ...! else:! form = BookForm(instance=obj)! return render(request, 'edit_book.html', {! 'book': book! 'form': form! })!
12. Example: Before urlpatterns = patterns('',! url(! r'^/book/(?P<book_id>\d+)/$',! book_view,! name='edit-book'! )! ...!
13. Example: After urlpatterns = patterns('',! url(! r'^/book/(?P<object_id>\d+)/$',! generic.update_object, {'model': Book,},! name='edit-book'! )! ...!
14. Example: After urlpatterns = patterns('',! url(! r'^/author/(?P<object_id>\d+)/$',! generic.update_object, {'model': Author,},! name='edit-author'! )! ...!
15. Problems • Configuration options limited by args • No control over logic flow • No re-use between views
16. Example: Before def edit_book(request, book_id):! try:! book = Book.objects.get(pk=book_id)! except Book.DoesNotExist:! raise Http404! if request.method == 'POST':! form = BookForm(! instance=book, ! data=request.POST)! if form.is_valid():! ! form.save()! return HttpResponseRedirect(! book.get_absolute_url())! ...
17. Example: Before def edit_book(request, book_id):! try:! book = Book.objects.get(pk=book_id)! except Book.DoesNotExist:! raise Http404! if request.method == 'POST':! form = BookForm(! instance=book, ! data=request.POST)! if form.is_valid():! book.prepare()! form.save()! return HttpResponseRedirect(! book.get_absolute_url())! ...
19. Let’s go class-based!
20. Django 1.3
21. OMFGBBQ!!1!!
22. What went wrong? • Fundamental confusion over purpose • Confusion over implementation choices • Ravioli Code • Bad documentation
23. Purpose • Two distinct, but connected bodies of work • Class Based Views • Class Based Generic Views
24. Class Based Views • A class based analog of a view function • Method-based HTTP-verb dispatch • ... and that’s it
25. Example from django.views.generic import View! ! ! class MyView(View):! def get(self, request, *args, **kwargs):! return render(request, 'myview.html' {})! ! def post(self, request, *args, **kwargs):! ...!
26. Class Based Views • Automatic OPTIONS request handling • Automatic naïve HEAD request handling • Automatic HTTP 405 on unknown verbs
27. CB Generic Views • Uses Class Based View as a base • Creates analogs of the old generic views • Addresses limits of functional approach
28. Implementation choices https://code.djangoproject.com/wiki/ClassBasedViews
29. Ravioli • Goal: Replace function-based generics with class-based generics • Show what class-based approach can do • End point views built out of mixins
30. freakboy3742’s
    Ravioli Cooking 101
31. Mixins def edit_view(): get object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return response
32. Mixins • UpdateView • BaseUpdateView • ModelFormMixin • FormMixin • SingleObjectMixin • ContextMixin • ProcessFormView • SingleObjectTemplate
 ResponseMixin • TemplateResponseMixin def edit_view(): get object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return response
33. Mixins • UpdateView • BaseUpdateView • ModelFormMixin • FormMixin • SingleObjectMixin • ContextMixin • ProcessFormView • SingleObjectTemplate
 ResponseMixin • TemplateResponseMixin def edit_view(): get object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return response
34. Mixins • UpdateView • BaseUpdateView • ModelFormMixin • FormMixin • SingleObjectMixin • ContextMixin • ProcessFormView • SingleObjectTemplate
 ResponseMixin • TemplateResponseMixin def edit_view(): get object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return response
35. Mixins • UpdateView • BaseUpdateView • ModelFormMixin • FormMixin • SingleObjectMixin • ContextMixin • ProcessFormView • SingleObjectTemplate
 ResponseMixin • TemplateResponseMixin def edit_view(): get object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return response
36. Mixins • CreateView • BaseCreateView • ModelFormMixin • FormMixin • SingleObjectMixin • ContextMixin • ProcessFormView • SingleObjectTemplate
 ResponseMixin • TemplateResponseMixin def create_view(): instantiate object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return response
37. Mixins • CreateView • BaseCreateView • ModelFormMixin • FormMixin • SingleObjectMixin • ContextMixin • ProcessFormView • SingleObjectJSON
 ResponseMixin def create_view(): instantiate object if POST: get form if form is valid: handle form redirect else: handle failure else: get form return JSON response
38. Example: After from django.views import generic! ! ! ! ! urlpatterns = patterns('',! url(! r'^/book/(?P<object_id>\d+)/$',! generic.update_object, {'model': Book,},! name='edit-book'! )! ...!
39. Example: After CBGV from django.views import generic! ! ! ! ! urlpatterns = patterns('',! url(! r'^/book/(?P<object_id>\d+)/$',! generic.UpdateView.as_view(model=Book),! name='edit-book'! )! ...!
40. Example: After CBGV from django.views import generic! ! class BookUpdateView(generic.UpdateView):! model = Book! ! urlpatterns = patterns('',! url(! r'^/book/(?P<object_id>\d+)/$',! BookUpdateView.as_view(),! name='edit-book'! )! ...!
41. Example: After CBGV class BookUpdateView(generic.UpdateView):! model = Book! ! def form_valid(self, form):! self.object.process()! return super(BookUpdateView, ! self).form_valid(form)!
42. Example: After CBGV from random import random! ! class PermissionsMixin(object):! def get_object(self, queryset=None):! if random() > 0.8:! raise Http404('Better luck next time')! else:! return super(PermissionsMixin, ! self).get_object(queryset)! ! class BookUpdateView(PermissionsMixin,! generic.UpdateView):! model = Book!
43. Ravioli tastes good! • Allows for reuse of core logic • Extremely flexible for inserting new logic • Easy to add your own mixins • But: You need to grok all the pieces
44. Documentation • Bad as originally released • Much better now • ccbv.co.uk • Still need framework decisions needed
45. Where to from here?
46. Have we solved the wrong problem?
47. Generic Views • Display a template • Display a single object • Display a list of objects • Display a form • Create, Update, Delete • Display a date archive
48. Modern web sites
    have different problems
49. Modern problems • Multiple forms/formsets per page • Continuous scrolling, not pagination • AJAX support (including in-place editing) • PJAX • Multiple “actions” per page • Rich, Javascript-driven UI
50. API-driven UI • A modern web site is an API with a UI • A user interface is: • a way to get meat to invoke an API • a way to visualize API results
51. API-driven UI in Django • APIs are easy • DRF, TastyPie and others. • Still need “views” • Navigation • Composition
52. All of this requires a strong base framework
53. Class-Based Views provide that framework
54. django.contrib.admin • Django’s admin is a class based view • Implemented using simple __call__() • Doesn’t have HTTP Verb support • Suffers from state problems
55. Doesn’t need to be part of Django core
56. Call to action • In discussion: Do you mean CBV or CBGV? • Docs can still be improved • #18830 - FormCollection • Experiment with APIs. • Django’s admin is a useful case study
57. Questions? http://djangoproject.org http://cecinestpasun.com russell@keith-magee.com @freakboy3742