Download pdf - Django class-based views: survival guide for novices (v2)

Leonardo Giordani - @tw_lgiordaniDjango class-based views – Survival guide for novices

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Django class-based viewsSurvival guide for novices

Leonardo Giordani

@tw_lgiordani – lgiordani.github.com


#2/82About me

Leonardo Giordanihttp://lgiordani.github.io

https://twitter.com/tw_lgiordani

https://github.com/lgiordani

https://plus.google.com/u/LeonardoGiordani

Feel free to contact meQuestions, suggestions, corrections are always warmly welcome


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Django novices who completed and understood the Django tutorial.

Knowledge of the basic Python OOP syntax and concepts is useful

(classes, inheritance, method overriding, function arguments processing).

About you


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What do you mean with “class-based”? What happened to

functional views?

How do I manage

forms with CBVs?

How can I change the

content of a view?

What is the advantage of

Class-Based views?

Get request object in class-based View

Where does self.kwargs

come from?

I hate Django class-based views

This is black magic, isn't it?


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What are Django views?


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Django is a processor of HTTP requests

DjangoHTTP REQUEST HTTP RESPONSE

Django views


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A view is the part of Django that processes a specific request

(a given set of URLs)

Django views

Django

view1

view2

HTTP REQUEST HTTP RESPONSE

UR

L d

isp

atch

er

Tem

pla

te e

ng

ineURL1

URL2


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view

enhanced view

A view (as any processing system) can be monolithic.

This makes hard to replace or enhance part of it.

Django views

HTTP REQUEST

HTTP REQUEST

HTTP RESPONSE

HTTP RESPONSE


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A system can be splitted in several components.

This makes easier to change part of it.

view:step1 view:step2 view:step3

view:step1 view:step2 view:step3

Django views

HTTP REQUEST

HTTP REQUEST

HTTP REQUEST

HTTP REQUEST


#10/82Object-oriented programming

Modularization

Small components that may be easily changed

Delegation

Inheritance and composition allow heavy code reuse


#11/82Class-based views

from django.views.generic.list import ListViewfrom articles.models import Articlefrom django.conf.urls import url

class ArticleListView(ListView): model = Article

urlpatterns = [ url(r'ârticles/$', ArticleListView.as_view()),]


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This routes HTTP requests to the 'articles/' URL to the ArticleListView view.


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This defines the view as a copy of ListView working on the

Article model.


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● Processes incoming HTTP GET requests

● Loads all Article objects

● Renders a template called article_list.html and the list of articles is in the

object_list variable



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What happens behind the scenes?


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Use the source, Luke!*

https://github.com/django/django

* Jeff Atwood, 2012


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Source is a moving target

https://github.com/django/django/tree/1.5.7


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@classonlymethoddef as_view(cls, **initkwargs): [...] def view(request, *args, **kwargs): [...] self.request = request self.args = args self.kwargs = kwargs return self.dispatch(request, *args, **kwargs) [...] return view

django/views/generic/base.py#L46

url(r'ârticles/$', ArticleListView.as_view())GETrequest

as_view

class View(object):


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as_view

class View(object):


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GETrequest

as_view

dispatch

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)


return self.dispatch(request, *args, **kwargs)

class View(object):


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GETrequest

as_view

dispatch




'GET' > getattr(self, 'get', [...])'POST' > getattr(self, 'post', [...])'PUT' > getattr(self, 'put', [...])[...]

class View(object):


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GETrequest

as_view

dispatch

get

return self.get(request, *args, **kwargs)

def get(self, request, *args, **kwargs): self.object_list = self.get_queryset() allow_empty = self.get_allow_empty() if not allow_empty: if (self.get_paginate_by(self.object_list) is not None and hasattr(self.object_list, 'exists')): is_empty = not self.object_list.exists() else: is_empty = len(self.object_list) == 0 if is_empty: raise Http404 [...] context = self.get_context_data(object_list=self.object_list) return self.render_to_response(context)

django/views/generic/list.py#L123

class BaseListView(MultipleObjectMixin, View):


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GETrequest

as_view

dispatch

get


def get(self, request, *args, **kwargs): self.object_list = self.get_queryset() allow_empty = self.get_allow_empty() if not allow_empty: if (self.get_paginate_by(self.object_list) is not None and hasattr(self.object_list, 'exists')): is_empty = not self.object_list.exists() else: is_empty = len(self.object_list) == 0 if is_empty: raise Http404 […] context = self.get_context_data(object_list=self.object_list) return self.render_to_response(context)




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GETrequest

as_view

dispatch

get

self.object_list = self.get_queryset()

def get_queryset(self): if self.queryset is not None: queryset = self.queryset if hasattr(queryset, '_clone'): queryset = queryset._clone() elif self.model is not None: queryset = self.model._default_manager.all() else: raise ImproperlyConfigured [...] return queryset

get_queryset


class MultipleObjectMixin(ContextMixin):


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GETrequest

as_view

dispatch

get

self.object_list = self.get_queryset()

def get_queryset(self): if self.queryset is not None: queryset = self.queryset if hasattr(queryset, '_clone'): queryset = queryset._clone() elif self.model is not None: queryset = self.model._default_manager.all() else: raise ImproperlyConfigured [...] return queryset

get_queryset





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GETrequest

as_view

dispatch

get






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GETrequest

as_view

dispatch

get

context = self.get_context_data(object_list=self.object_list)

def get_context_data(self, **kwargs): queryset = kwargs.pop('object_list') page_size = self.get_paginate_by(queryset) context_object_name = self.get_context_object_name(queryset) if page_size: [...] else: context = { 'paginator': None, 'page_obj': None, 'is_paginated': False, 'object_list': queryset } if context_object_name is not None: context[context_object_name] = queryset context.update(kwargs) return super(MultipleObjectMixin, self).get_context_data(**context)

get_context_data




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GETrequest

as_view

dispatch

get



get_context_data




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GETrequest

as_view

dispatch

get

context_object_name = self.get_context_object_name(queryset)

def get_context_object_name(self, object_list): if self.context_object_name: return self.context_object_name elif hasattr(object_list, 'model'): return '%s_list' % object_list.model._meta.object_name.lower() else: return None

get_context_data


get_context_object_name




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GETrequest

as_view

dispatch

get






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GETrequest

as_view

dispatch

get

return self.render_to_response(context)

def render_to_response(self, context, **response_kwargs): response_kwargs.setdefault('content_type', self.content_type) return self.response_class( request = self.request, template = self.get_template_names(), context = context, **response_kwargs )


render_to_response

class TemplateResponseMixin(object):


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GETrequest

as_view

dispatch

get

return self.render_to_response(context)

def render_to_response(self, context, **response_kwargs): response_kwargs.setdefault('content_type', self.content_type) return self.response_class( request = self.request, template = self.get_template_names(), context = context, **response_kwargs )


render_to_response



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GETrequest

as_view

dispatch

get

template = self.get_template_names()

def get_template_names(self): try: names = super(MultipleObjectTemplateResponseMixin, self).get_template_names() except ImproperlyConfigured: names = []

if hasattr(self.object_list, 'model'): opts = self.object_list.model._meta names.append("%s/%s%s.html" % (opts.app_label, opts.object_name.lower(), self.template_name_suffix))

return names


render_to_response

get_template_names

class MultipleObjectTemplateResponseMixin(TemplateResponseMixin):


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GETrequest

as_view

dispatch

get

names = super([...]).get_template_names()

def get_template_names(self): if self.template_name is None: raise ImproperlyConfigured([...]) else: return [self.template_name]


render_to_response

get_template_names

get_template_names



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GETrequest

as_view

dispatch

get

template = self.get_template_names()

def get_template_names(self): try: names = super(MultipleObjectTemplateResponseMixin, self).get_template_names() except ImproperlyConfigured: names = []

if hasattr(self.object_list, 'model'): opts = self.object_list.model._meta names.append("%s/%s%s.html" % (opts.app_label, opts.object_name.lower(), self.template_name_suffix))

return names


render_to_response

get_template_names

class MultipleObjectTemplateResponseMixin(TemplateResponseMixin):


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● Processes incoming HTTP GET requests

● Loads all Article objects

● Renders a template called article_list.html and the list of articles is in

the object_list variable



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How do you customize CBVs behaviour?


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GETrequest

as_view



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GETrequest

as_view

dispatch

get

get_context_data


def get_context_data(self, **kwargs): context = super(ArticleListView, self).get_context_data(**kwargs) context['readers'] = Reader.objects.count() return context

def get_context_data(self, **kwargs): [...]

views/generic/list.py#L91


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GETrequest

as_view

dispatch

get

get_queryset


def get_queryset(self): queryset = super(ArticleListView, self).get_queryset() return queryset.filter([...])

def get_queryset(self): [...]

views/generic/list.py#L91


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Arguments in class-based views


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as_view

class View(object):


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as_view

class View(object):


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GETrequest

as_view

dispatch

get

get_queryset


def get_queryset(self): queryset = super(ArticleListView, self).get_queryset() return queryset.filter(year=self.kwargs['year'])

https://docs.djangoproject.com/en/1.5/topics/http/urls/

url(r'ârticles/(?P<year>\d{4})/$', ArticleListView.as_view()),


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GETrequest

as_view

dispatch

get

get_context_data


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

https://docs.djangoproject.com/en/1.5/topics/http/urls/

url(r'ârticles/(?P<year>\d{4})/$', ArticleListView.as_view()),


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GETrequest

as_view

dispatch

get



get_context_data




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GETrequest

as_view

dispatch

get



get_context_data




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GETrequest

as_view

dispatch

get

return super(MultipleObjectMixin, self).get_context_data(**context)

def get_context_data(self, **kwargs): if 'view' not in kwargs: kwargs['view'] = self return kwargs

get_context_data

django/views/generic/base.py#15

get_context_data

class ContextMixin(object):


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

urlpatterns = [ url(r'ârticles/(?P<year>\d{4})/$', ArticleListView.as_view())]


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urlpatterns = [ url(r'ârticles/(?P<year>\d{4})/$', ArticleListView.as_view())]

[...]{{ view.kwargs.year }}[...]

http://reinout.vanrees.org/weblog/2014/05/19/context.html


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ListView

MultipleObjectTemplateResponseMixin BaseListView

TemplateResponseMixin MultipleObjectMixin View

ContextMixin


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ListView

MultipleObjectTemplateResponseMixin BaseListView

TemplateResponseMixin MultipleObjectMixin View

ContextMixinas_view()dispatch()as_view()dispatch()

get_context_data()

render_to_response()get_template_names()

get_queryset()get_context_data()get_context_object_name()

get()

get_template_names()


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CRUD operations and forms


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A Read operation is performed through a GET request,

while Create, Update and Delete are implemented with

other HTTP methods: POST, PUT, DELETE


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GETrequest

as_view

dispatch




'GET' > getattr(self, 'get', [...])'POST' > getattr(self, 'post', [...])'PUT' > getattr(self, 'put', [...])[...]

class View(object):


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class RedirectView(View): def get(self, request, *args, **kwargs): [...] return http.HttpResponseRedirect(url)

def head(self, request, *args, **kwargs): return self.get(request, *args, **kwargs)

def post(self, request, *args, **kwargs): return self.get(request, *args, **kwargs)

def options(self, request, *args, **kwargs): return self.get(request, *args, **kwargs)

def delete(self, request, *args, **kwargs): return self.get(request, *args, **kwargs)

def put(self, request, *args, **kwargs): return self.get(request, *args, **kwargs)



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What is the relationship between

forms and HTTP methods?


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browser server

GET request

POST request

HTTP response

HTTP response

When you work with forms there are multiple interactions

with the view


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from django.shortcuts import renderfrom django.http import HttpResponseRedirect

def contact(request): if request.method == 'POST': # If the form has been submitted... form = ContactForm(request.POST) # A form bound to the POST data if form.is_valid(): # All validation rules pass # Process the data in form.cleaned_data # ... return HttpResponseRedirect('/thanks/') # Redirect after POST else: form = ContactForm() # An unbound form

return render(request, 'contact.html', {'form': form,})


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● Processes incoming HTTP GET and POST requests

● Renders a template called stickynote_form.html and the editing form is

in the form variable

● Manages the creation (update, deletion) of a StickyNote entry

class NoteAdd(CreateView): model = StickyNote


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POSTrequest

as_view

dispatch

post

return self.post(request, *args, **kwargs)

def post(self, request, *args, **kwargs): self.object = None return super(BaseCreateView, self).post(request, *args, **kwargs)

django/views/generic/edit.py#L197

class BaseCreateView(ModelFormMixin, ProcessFormView):


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POSTrequest

as_view

dispatch

post

return super().post(request, *args, **kwargs)

def post(self, request, *args, **kwargs): form_class = self.get_form_class() form = self.get_form(form_class) if form.is_valid(): return self.form_valid(form) else: return self.form_invalid(form)


post

class ProcessFormView(View):


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POSTrequest

as_view

dispatch

post





post


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POSTrequest

as_view

dispatch

post

form_class = self.get_form_class()


class ModelFormMixin(FormMixin, SingleObjectMixin):

post

get_form_class

def get_form_class(self): if self.form_class: return self.form_class else: if self.model is not None: model = self.model elif hasattr(self, 'object') and self.object is not None: model = self.object.__class__ else: model = self.get_queryset().model return model_forms.modelform_factory(model)


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POSTrequest

as_view

dispatch

post



post

get_form_class

def get_form_class(self): if self.form_class: return self.form_class else: if self.model is not None: model = self.model elif hasattr(self, 'object') and self.object is not None: model = self.object.__class__ else: model = self.get_queryset().model return model_forms.modelform_factory(model)

form_class = self.get_form_class()


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POSTrequest

as_view

dispatch

post




post



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POSTrequest

as_view

dispatch

post

form = self.get_form(form_class)

def get_form(self, form_class): return form_class(**self.get_form_kwargs())


class FormMixin(ContextMixin):

post

get_form


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POSTrequest

as_view

dispatch

post

return form_class(**self.get_form_kwargs())

def get_form_kwargs(self): kwargs = super(ModelFormMixin, self).get_form_kwargs() kwargs.update({'instance': self.object}) return kwargs



post

get_form_kwargs


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POSTrequest

as_view

dispatch

post

kwargs = super().get_form_kwargs()

def get_form_kwargs(self, form_class): kwargs = {'initial': self.get_initial()} if self.request.method in ('POST', 'PUT'): kwargs.update({ 'data': self.request.POST, 'files': self.request.FILES, }) return kwargs



post

get_form_kwargs

get_form_kwargs


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POSTrequest

as_view

dispatch

post




post



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POSTrequest

as_view

dispatch

post

return self.form_valid(form)


def form_valid(self, form): self.object = form.save() return super(ModelFormMixin, self).form_valid(form)


post

form_valid


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POSTrequest

as_view

dispatch

post

return super().form_valid(form)


def form_valid(self, form): return HttpResponseRedirect(self.get_success_url())

post

form_valid

form_valid



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POSTrequest

as_view

dispatch

post

return HttpResponseRedirect(self.get_success_url())


def get_success_url(self): if self.success_url: url = self.success_url % self.object.__dict__ else: try: url = self.object.get_absolute_url() except AttributeError: raise ImproperlyConfigured([...]) return url

post

...

get_success_url



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POSTrequest

as_view

dispatch

post

return self.post(request, *args, **kwargs)

def form_invalid(self, form): return self.render_to_response( self.get_context_data(form=form))



post

form_invalid


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CreateView

SingleObjectTemplateResponseMixinBaseCreateView

TemplateResponseMixin

ModelFormMixin ProcessFormView

FormMixin SingleObjectMixin

ContextMixin

View


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Online resources


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Digging Up Django Class-based Views

http://lgiordani.github.io/blog/categories/django/


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Classy Class-Based Views: Django CBVs browser

http://ccbv.co.uk/


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Django Vanilla Views

http://djangovanillaviews.org/


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Class Based Views and Dry Ravioli

http://lukeplant.me.uk/blog/posts/classbased

viewsanddryravioli/

Django's CBVs were a mistake

http://lukeplant.me.uk/blog/posts/djangoscbvs

wereamistake/


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Some links to better understand Python OOP

http://www.reddit.com/r/Python/

comments/226ahl/some_links_about_python_oop/

About using the source code

http://blog.codinghorror.com/

learntoreadthesourceluke/


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Thank you!Questions? Comments? Advice?