Overcoming Troubles with Class-Based (Generic) Views

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

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afrg.co/otwcbv

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shameless

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Basic Project

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

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Pages Account List Account Detail Account Create Transaction Create

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Refactoring to Class-Based Views

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

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# 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})

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# 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})

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# 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})

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# 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'âccount/$', AccountList.as_view(), name='bank_account_list'), url(r'âccount/create/$', AccountCreate.as_view(), name='bank_account_create'), url(r'âccount/(?P[\w\-]+)/$', AccountDetail.as_view(), name='bank_account_detail'), url(r'^transaction/$', TransactionCreate.as_view(), name='bank_trans_create'), )

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Taking advantage of CBVs

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

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# 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})

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# 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'

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# 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

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# 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

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# 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})

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Class-Based Generic Views

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# 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')

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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'âccount/$', ListView.as_view(model=Account), name='bank_account_list'), url(r'âccount/create/$', CreateView.as_view(model=Account), name='bank_account_create'), url(r'âccount/(?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'), )

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Quick Recap

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Customizing CBGVs

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

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

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@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

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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)

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

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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)

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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)

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

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

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# 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

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Automating Slug slugify() clean()

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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

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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

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

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Saving slug BaseModelForm.save() save_instance save_m2m construct_instance

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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

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Transaction Forms To Account From Account

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

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class TransactionCreate(CreateView): model = Transaction

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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)

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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

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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)

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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')

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Congratulations!

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

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

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Thank you! afrg.co/otwcbv @andrewsforge