django class-based views: survival guide for novices (v2)

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

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

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

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?

What are Django views?

Django is a processor of HTTP requests

DjangoHTTP REQUEST HTTP RESPONSE

Django views

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

(a given set of URLs)

Django views

Django

HTTP REQUEST HTTP RESPONSE

ineURL1

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 RESPONSE

A system can be splitted in several components.

This makes easier to change part of it.

view:step1 view:step2 view:step3

Django views

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'^articles/$', ArticleListView.as_view()),]

#12/82

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

#13/82

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

Article model.

#14/82

● 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

#15/82

What happens behind the scenes?

#16/82

Use the source, Luke!*

https://github.com/django/django

* Jeff Atwood, 2012

#17/82

Source is a moving target

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

#18/82

@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'^articles/$', ArticleListView.as_view())GETrequest

as_view

class View(object):

#19/82

as_view

class View(object):

#20/82

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):

#21/82

GETrequest

as_view

dispatch

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

class View(object):

#22/82

GETrequest

as_view

dispatch

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):

#23/82

GETrequest

as_view

dispatch

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)

#24/82

GETrequest

as_view

dispatch

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):

#25/82

GETrequest

as_view

dispatch

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

#26/82

GETrequest

as_view

dispatch

#27/82

GETrequest

as_view

dispatch

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

#28/82

GETrequest

as_view

dispatch

get_context_data

#29/82

GETrequest

as_view

dispatch

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

#30/82

GETrequest

as_view

dispatch

#31/82

GETrequest

as_view

dispatch

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):

#32/82

GETrequest

as_view

dispatch

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

#33/82

GETrequest

as_view

dispatch

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):

#34/82

GETrequest

as_view

dispatch

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

#35/82

GETrequest

as_view

dispatch

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):

#36/82

● 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

#37/82

How do you customize CBVs behaviour?

#38/82

GETrequest

as_view

#39/82

GETrequest

as_view

dispatch

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

#40/82

GETrequest

as_view

dispatch

get_queryset

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

def get_queryset(self): [...]

views/generic/list.py#L91

#41/82

Arguments in class-based views

#42/82

as_view

class View(object):

#43/82

as_view

class View(object):

#44/82

GETrequest

as_view

dispatch

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'^articles/(?P<year>\d{4})/$', ArticleListView.as_view()),

#45/82

GETrequest

as_view

dispatch

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'^articles/(?P<year>\d{4})/$', ArticleListView.as_view()),

#46/82

GETrequest

as_view

dispatch

get_context_data

#47/82

GETrequest

as_view

dispatch

get_context_data

#48/82

GETrequest

as_view

dispatch

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):

#49/82

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

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

#50/82

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

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

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

#51/82

ListView

MultipleObjectTemplateResponseMixin BaseListView

TemplateResponseMixin MultipleObjectMixin View

ContextMixin

#52/82

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_template_names()

#53/82

CRUD operations and forms

#54/82

A Read operation is performed through a GET request,

while Create, Update and Delete are implemented with

other HTTP methods: POST, PUT, DELETE

#55/82

GETrequest

as_view

dispatch

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

class View(object):

#56/82

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)

#57/82

What is the relationship between

forms and HTTP methods?

#58/82

browser server

GET request

POST request

HTTP response

When you work with forms there are multiple interactions

with the view

#59/82

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,})

#60/82

● 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

#61/82

POSTrequest

as_view

dispatch

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):

#62/82

POSTrequest

as_view

dispatch

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)

class ProcessFormView(View):

#63/82

POSTrequest

as_view

dispatch

#64/82

POSTrequest

as_view

dispatch

form_class = self.get_form_class()

class ModelFormMixin(FormMixin, SingleObjectMixin):

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)

#65/82

POSTrequest

as_view

dispatch

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()

#66/82

POSTrequest

as_view

dispatch

#67/82

POSTrequest

as_view

dispatch

form = self.get_form(form_class)

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

class FormMixin(ContextMixin):

get_form

#68/82

POSTrequest

as_view

dispatch

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

get_form_kwargs

#69/82

POSTrequest

as_view

dispatch

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

get_form_kwargs

#70/82

POSTrequest

as_view

dispatch

#71/82

POSTrequest

as_view

dispatch

return self.form_valid(form)

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

form_valid

#72/82

POSTrequest

as_view

dispatch

return super().form_valid(form)

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

form_valid

#73/82

POSTrequest

as_view

dispatch

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

get_success_url

#74/82

POSTrequest

as_view

dispatch

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

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

form_invalid

#75/82

CreateView

SingleObjectTemplateResponseMixinBaseCreateView

TemplateResponseMixin

ModelFormMixin ProcessFormView

FormMixin SingleObjectMixin

ContextMixin

#76/82

Online resources

#77/82

Digging Up Django Class-based Views

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

#78/82

Classy Class-Based Views: Django CBVs browser

http://ccbv.co.uk/

#79/82

Django Vanilla Views

http://djangovanillaviews.org/

#80/82

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/

#81/82

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/

#82/82

Thank you!Questions? Comments? Advice?

django class-based views: survival guide for novices (v2)

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