Overcoming Troubles with Class-Based (Generic) Views

An introduction to Class-Based Views and Class-Based Generic Views. Talk given at DjangoCon 2013.

Transcript

1. Overcoming Troubles with
   Class Based (Generic) Views
   A short guide to managing the beast
   

   View Slide

2. afrg.co/otwcbv
   

   View Slide

3. shameless
   

   View Slide

4. © DREAMWORKS 2010
   

   View Slide

5. Basic Project
   

   View Slide

6. Project Description
   Two Models: Account & Transaction
   Account: slug, get_absolute_url()
   Transaction: two FK’s to Account
   ModelForms for both
   

   View Slide

7. Pages
   Account List
   Account Detail
   Account Create
   Transaction Create
   

   View Slide

8. Refactoring to
   Class-Based Views
   

   View Slide

9. # bank/views.py
   from django.views.generic import View
   

   View Slide

10. # bank/views.py
    class AccountList(View):
    def get(self, request):
    acct_list = Account.objects.all()
    return render(request,
    'bank/account_list.html',
    {'account_list': acct_list})
    class AccountDetail(View):
    def get(self, request, slug):
    acct = get_object_or_404(Account, slug=slug)
    return render(request,
    'bank/account_detail.html',
    {'account': acct})
    

    View Slide

11. # bank/views.py
    class AccountCreate(View):
    def get(self, request):
    form = AccountForm()
    return render(request,
    'bank/account_form.html',
    {'form': form})
    def post(self, request):
    form = AccountForm(request.POST)
    if form.is_valid():
    new_acct = form.save()
    return redirect(new_acct)
    else:
    return render(request,
    'bank/account_form.html',
    {'form': form})
    

    View Slide

12. # bank/views.py
    class TransactionCreate(View):
    def get(self, request):
    form = TransactionForm()
    return render(request,
    'bank/account_form.html',
    {'form': form})
    def post(self, request):
    form = TransactionForm(request.POST)
    if form.is_valid():
    new_acct = form.save()
    return redirect('bank_account_list')
    else:
    return render(request,
    'bank/account_form.html',
    {'form': form})
    

    View Slide

13. # bank/views.py
    class TransactionCreate(View):
    def get(self, request):
    form = TransactionForm()
    return render(request,
    'bank/account_form.html',
    {'form': form})
    def post(self, request):
    form = TransactionForm(request.POST)
    if form.is_valid():
    new_acct = form.save()
    return redirect('bank_account_list')
    else:
    return render(request,
    'bank/account_form.html',
    {'form': form})
    

    View Slide

14. # bank/urls.py
    from django.conf.urls import patterns, url
    from .models import Account
    from .views import AccountList, AccountDetail, \
    AccountCreate, TransactionCreate
    urlpatterns = patterns('',
    url(r'^account/$',
    AccountList.as_view(),
    name='bank_account_list'),
    url(r'^account/create/$',
    AccountCreate.as_view(),
    name='bank_account_create'),
    url(r'^account/(?P[\w\-]+)/$',
    AccountDetail.as_view(),
    name='bank_account_detail'),
    url(r'^transaction/$',
    TransactionCreate.as_view(),
    name='bank_trans_create'),
    )
    

    View Slide

15. Taking advantage of CBVs
    

    View Slide

16. # bank/views.py
    class PostFormMixin(object):
    form = None
    template = ''
    redirect = ''
    

    View Slide

17. # bank/views.py
    class PostFormMixin(object):
    ...
    def get(self, request):
    form = self.form()
    return render(request,
    self.template,
    {'form': form})
    def post(self, request):
    form = self.form(request.POST)
    if form.is_valid():
    new_obj = form.save()
    if self.redirect:
    return redirect(self.redirect)
    else:
    return redirect(new_obj)
    else:
    return render(request,
    self.template,
    {'form': form})
    

    View Slide

18. # bank/views.py
    class AccountCreate(PostFormMixin, View):
    form = AccountForm
    template = 'bank/account_form.html'
    class TransactionCreate(PostFormMixin, View):
    form = TransactionForm
    template = 'bank/account_form.html'
    redirect = 'bank_account_list'
    

    View Slide

19. # bank/views.py
    class PostFormMixin(object):
    ...
    def get_template(self):
    if self.template == '':
    raise ImproperlyConfigured(
    '"template" variable not defined in %s'
    % self.__class__.__name__)
    return self.template
    

    View Slide

20. # bank/views.py
    class PostFormMixin(object):
    ...
    def get_redirect_url(self,obj):
    if self.redirect:
    url = self.redirect
    else:
    try:
    url = obj.get_absolute_url()
    except AttributeError:
    raise ImproperlyConfigured(
    '"redirect" variable must be defined '
    'in %s when redirecting %s objects.'
    % (self.__class__.__name__,
    obj.__class__.__name__))
    return url
    

    View Slide

21. # bank/views.py
    class PostFormMixin(object):
    ...
    def get(self, request):
    form = self.form()
    return render(request,
    self.get_template(),
    {'form': form})
    def post(self, request):
    form = self.form(request.POST)
    if form.is_valid():
    new_obj = form.save()
    return redirect(self.get_redirect_url(new_obj))
    else:
    return render(request,
    self.get_template(),
    {'form': form})
    

    View Slide

22. Class-Based Generic Views
    

    View Slide

23. # bank/views.py
    from django.core.urlresolvers import reverse_lazy
    from django.views.generic import (ListView, DetailView,
    CreateView)
    from .models import Account, Transaction
    class AccountList(ListView):
    model = Account
    class AccountDetail(DetailView):
    model = Account
    class AccountCreate(CreateView):
    model = Account
    class TransactionCreate(CreateView):
    model = Transaction
    success_url = reverse_lazy('bank_account_list')
    

    View Slide

24. from django.conf.urls import patterns, url
    from django.core.urlresolvers import reverse_lazy
    from django.views.generic import (ListView, DetailView,
    CreateView)
    from .models import Account, Transaction
    urlpatterns = patterns('',
    url(r'^account/$',
    ListView.as_view(model=Account),
    name='bank_account_list'),
    url(r'^account/create/$',
    CreateView.as_view(model=Account),
    name='bank_account_create'),
    url(r'^account/(?P[\w\-]+)/$',
    DetailView.as_view(model=Account),
    name='bank_account_detail'),
    url(r'^transaction/$',
    CreateView.as_view(model=Transaction,
    success_url=reverse_lazy(
    'bank_account_list')),
    name='bank_trans_create'),
    )
    

    View Slide

25. Quick Recap
    

    View Slide

26. Customizing CBGVs
    

    View Slide

27. Feature Changes
    List Accounts and Transactions in AccountList
    Split TransactionCreate
    Send To link
    Send From link
    Generate Slug Automatically
    

    View Slide

28. View Slide

29. View Slide

30. Multiple Inheritance
    New Style-classes (object) in Python 2.2
    C3 MRO in Python 2.3
    

    View Slide

31. View Slide

32. View Slide

33. View Slide

34. @classonlymethod
    def as_view(cls, **initkwargs):
    for key in initkwargs:
    if key in cls.http_method_names:
    raise TypeError('...')
    if not hasattr(cls, key):
    raise TypeError('...')
    def view(request, *args, **kwargs):
    ...
    update_wrapper(view, cls, updated=())
    update_wrapper(view, cls.dispatch, assigned=())
    return view
    

    View Slide

35. def as_view(cls, **initkwargs):
    ...
    def view(request, *args, **kwargs):
    self = cls(**initkwargs)
    if hasattr(self, 'get') and not hasattr(self, 'head'):
    self.head = self.get
    self.request = request
    self.args = args
    self.kwargs = kwargs
    return self.dispatch(request, *args, **kwargs)
    

    View Slide

36. def __init__(self, **kwargs):
    for key, value in six.iteritems(kwargs):
    setattr(self, key, value)
    

    View Slide

37. def dispatch(self, request, *args, **kwargs):
    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)
    

    View Slide

38. http_method_names = ['get', 'post', 'put',
    'delete', 'head', 'options', 'trace']
    def dispatch(self, request, *args, **kwargs):
    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)
    

    View Slide

39. © TECHNABOB.COM 2012
    

    View Slide

40. CBGV
    TemplateView
    RedirectView
    DetailView
    ListView
    FormView
    CreateView
    UpdateView
    DeleteView
    ArchiveIndexView
    YearArchiveView
    MonthArchiveView
    WeekArchiveView
    DayArchiveView
    TodayArchiveView
    DateDetailView
    

    View Slide

41. View Slide

42. © DISNEY 2012
    

    View Slide

43. © MARVEL 2013
    

    View Slide

44. View Slide

45. © WARNER BROS 1942
    

    View Slide

46. © MGM 1995
    

    View Slide

47. Transaction List
    ListView.get()
    ListView.get_context_data()
    MultipleObjectMixin
    ContextMixin
    

    View Slide

48. # bank/views.py
    class AccountList(ListView):
    model = Account
    def get_context_data(self, **kwargs):
    context = super(AccountList, self)\
    .get_context_data(**kwargs)
    context['transaction_list'] = Transaction\
    .objects\
    .order_by('-date')\
    [:10]
    return context
    

    View Slide

49. Automating Slug
    slugify()
    clean()
    

    View Slide

50. from django.forms import ModelForm
    from django.utils.text import slugify
    from .models import Account
    class AccountForm(ModelForm):
    class Meta:
    model = Account
    def clean(self):
    cleaned_data = super(AccountForm, self).clean()
    name = cleaned_data.get("name")
    slug = cleaned_data.get("slug")
    if not slug and name:
    cleaned_data['slug'] = slugify(name)
    return cleaned_data
    

    View Slide

51. from django.forms import ModelForm
    from django.utils.text import slugify
    from .models import Account
    class AccountForm(ModelForm):
    class Meta:
    model = Account
    exclude = ('slug',)
    def clean(self):
    cleaned_data = super(AccountForm, self).clean()
    name = cleaned_data.get("name")
    slug = cleaned_data.get("slug")
    if not slug and name:
    cleaned_data['slug'] = slugify(name)
    return cleaned_data
    

    View Slide

52. Saving slug
    django-src/forms/models.py
    ModelForm
    ModelFormMetaclass
    BaseModelForm
    

    View Slide

53. Saving slug
    BaseModelForm.save()
    save_instance
    save_m2m
    construct_instance
    

    View Slide

54. class AccountForm(ModelForm):
    class Meta:
    model = Account
    exclude = ('slug',)
    def save(self, commit=True):
    instance = super(AccountForm, self)\
    .save(commit=False)
    instance.slug = slugify(
    self.cleaned_data\
    .get('name', ''))
    if commit:
    instance.save()
    self.save_m2m()
    return instance
    

    View Slide

55. Transaction Forms
    To Account
    From Account
    

    View Slide

56. Overrides
    Introduce two new forms
    get_initial()
    get_context_data()
    view() -> dispatch() -> get()/post()
    get_success_url()
    

    View Slide

57. class TransactionCreate(CreateView):
    model = Transaction
    

    View Slide

58. class TransactionCreate(CreateView):
    ...
    def dispatch(self, request, *args, **kwargs):
    slug = kwargs.get('slug', None)
    account_obj = get_object_or_404(Account,\
    slug__iexact=slug)
    self.acct_name = account_obj.name
    self.acct_pk = account_obj.pk
    self.acct_url = getattr(account_obj,\
    'get_absolute_url', '')
    return super(TransactionCreate, self)\
    .dispatch(request, *args, **kwargs)
    

    View Slide

59. class TransactionCreate(CreateView):
    ...
    def get_initial(self):
    initial_data = super(TransactionCreate, self)\
    .get_initial()
    if self.form_class == TransferFormFrom:
    initial_data['from_account'] = self.acct_pk
    elif self.form_class == TransferFormTo:
    initial_data['to_account'] = self.acct_pk
    else:
    raise ImproperlyConfigured(
    '"form_class" variable must be defined
    'in %s for correct initial behavior.'
    % (self.__class__.__name__,
    obj.__class__.__name__))
    return initial_data
    

    View Slide

60. class TransactionCreate(CreateView):
    ...
    def get_context_data(self, **kwargs):
    context = {}
    context['account_name'] = self.acct_name
    if self.form_class == TransferFormFrom:
    context['trans_dir'] = 'From:'
    elif self.form_class == TransferFormTo:
    context['trans_dir'] = 'To:'
    else:
    raise ImproperlyConfigured(
    '"form_class" variable must be defined
    'in %s for correct initial behavior.'
    % (self.__class__.__name__,
    obj.__class__.__name__))
    context.update(kwargs)
    return super(TransactionCreate, self)\
    .get_context_data(**context)
    

    View Slide

61. class TransactionCreate(CreateView):
    ...
    def get_success_url(self):
    if (hasattr(self, 'acct_url')
    and self.acct_url != ''):
    return self.acct_url()
    else:
    return reverse('bank_account_list')
    

    View Slide

62. Congratulations!
    

    View Slide

63. © DREAMWORKS 2010
    

    View Slide

64. Take Aways
    CBV ≠ CBGV
    Full understanding: MRO, View
    ccbv.co.uk
    CBGV: Lasagna is a sometimes food
    

    View Slide

65. View Slide

66. Take Aways
    CBV ≠ CBGV
    Full understanding: MRO, View
    ccbv.co.uk
    CBGV: Lasagna is a sometimes food
    

    View Slide

67. Thank you!
    afrg.co/otwcbv
    @andrewsforge
    

    View Slide