Django Views: Functions, Classes, and Generics

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ANDREW PINKHAM TOPIC DATE AUTHOR SEPTEMBER 2015 VIEWS: FUNCTIONS, CLASSES & GENERICS DJANGOCON US 2015

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$ whoami Software Engineer Freelance Consultant Technical Instructor Andrew Pinkham Hi, I’m

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AUTHOR OF DJANGO UNLEASHED AVAILABLE FOR PREORDER; SHIPS DECEMBER 2015

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Answers today: Django handles HTTP for me! Why do I have to worry about it? When is Django deprecating function views? Aren’t all class-based views generic? How do I choose what kind of view to use?

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$ ls views 1_fundamentals 2_views 3_tools

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$ ls views 1_fundamentals -> problem, meet solution 2_views -> examining the solution 3_tools -> making the solution easier

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$ less views/1_fundamentals What is a callable? What is HTTP, anyway? Django's HTTP request/response cycle A view’s purpose

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$ less views/2_views A Brief History of Views Functions Views Class Based Views Generic Class Based Views

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$ less views/3_tools Enhance! When to Use What

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afrg.co/views

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PYTHON CALLABLES UNDERSTANDING THE PROBLEM

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def a_function(*args, **kwargs): return 'Hello DjangoCon 2015!' >>> a_function() 'Hello DjangoCon 2015!'

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>>> lambda_function = lambda: 'Enjoying Austin?' >>> lambda_function() 'Enjoying Austin?'

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class FirstClass: an_attribute = ( 'Have you visited any good restaurants?') def a_method(*args, **kwargs): self = args[0] return self.an_attribute >>> fc_obj = FirstClass() >>> fc_obj.a_method() 'Have you visited any good restaurants?'

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class SecondClass(FirstClass): def __init__(self): """Magic method to initialize a class""" self.an_attribute = ( "Easy Tiger, La Condessa and " "Lambert's are my favorites.") >>> sc_obj = SecondClass() >>> sc_obj.a_method() "Easy Tiger, La Condessa and Lambert's are my favorites."

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class ThirdClass(SecondClass): def __call__(*args, **kwargs): """Magic method to make object callable""" return ( "I like grabbing ice cream at " "Amy's, too.") >>> tc_obj = ThirdClass() >>> tc_obj() "I like grabbing ice cream at Amy's, too."

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>>> callable(a_function) True >>> callable(lambda_function) True >>> callable(FirstClass) True >>> callable(fc_obj) False >>> callable(sc_obj) False >>> callable(tc_obj) True

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WHAT IS HTTP, ANYWAY? UNDERSTANDING THE PROBLEM

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HyperText Transfer Protocol Deﬁnes a client and server how to communicate HTTP Request Methods HTTP Response Codes Safe Methods and Idempotent Methods

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HyperText Transfer Protocol Methods GET HEAD OPTIONS POST PUT Codes 200 400 403 404 500

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HyperText Transfer Protocol Idempotent Methods POST PUT

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Your website must adhere to HTTP

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Andrew’s Server Request Methods GIMME HAVE Response Code CANHAS NOPE

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Your website must adhere to HTTP

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Goal of Software Solve a Problem Automate Behavior

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Goal of Software Solve a Problem Automate Behavior

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HTTP is the problem web frameworks solve You are the behavior frameworks automate

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DJANGO’S REQUEST/RESPONSE CYCLE UNDERSTANDING THE PROBLEM

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What is a view? 'A view is a "type" of Web page' "views are for displaying content" (DORK-1) Dynamic generation of content

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Step 3. HTTP Response Step 1. HTTP Request Website Step 2. Computation

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Database Views URL Dispatch URL Patterns Template Loader Template Files Models Forms Context Processors

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Simpliﬁcation No WSGI Server No View Middleware No Exception Handling

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Views URL Dispatch URL Patterns

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Views URL Patterns METHOD /path/to/resource/ HTTP/1.1

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Views URL Patterns METHOD /path/to/resource/ HTTP/1.1 METHOD /path/to/resource/ HTTP/1.1

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Views URL Patterns METHOD /path/to/resource/ HTTP/1.1 METHOD /path/to/resource/ HTTP/1.1

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What is a view? Accept HttpRequest object Generate data based on: HTTP request method Request data (POST, PUT, etc) Data from dispatch (from the URL path) Return HttpResponse object

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What is a view? Any Python Callable

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Why do we talk about functions and classes (and generics)?

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A BRIEF HISTORY OF VIEWS FROM WHEN DINOSAURS STILL ROAMED THE EARTH UNTIL THE ROBOT APOCALYPSE

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A Brief History of Views July 2005: Django Function views in original tarball July 2005: Generic views in SVN revision 304

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Functions are Rigid Extend generic views? Use classes!

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The big win from a class-based view is [...] being able to override parts of the behavior without needing to rewrite the entire view, or add 101 parameters. –Alex Gaynor https://groups.google.com/d/msg/django-developers/J87Hm3hO9z8/gWunEs9QwMwJ

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A Brief History of Views July 2005: Django Function views in original tarball July 2005: Generic views in SVN revision 304 March 2008: Joseph Kocherhans #6735

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Class-Based Views Simple (Usable - principle of least surprise) Extendable Inheritance Decorators Safe (Thread-Safe) Testable

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A Brief History of Views July 2005: Django Function views in original tarball July 2005: Generic views in SVN revision 304 March 2008: Joseph Kocherhans #6735 March 2011: (G)CBV Released in Django 1.3

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The Naming Problem Generic Views Class-Based Views (CBV) Class-Based + Generic Views (CBGV)

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The Naming Problem Object Views Generic (Class-Based) Views (GCBV)

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State of the Pony Function Views Object Views (Class-Based Views) Generic (Class-Based) Views

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FUNCTION VIEWS HOW I LEARNED TO STOP WORRYING AND LOVE NON-COMPLIANCE

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class ExampleModel(models.Model): name = models.CharField(max_length=31) slug = models.SlugField(max_length=31) def __str__(self): return self.name.title()

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from django.conf.urls import url from . import views urlpatterns = [ url(r'^(?P[\w\-]+)/$', views.model_detail, name='model_detail'), ]

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from django.shortcuts import ( get_object_or_404, render) from .models import ExampleModel def model_detail(request, *args, **kwargs): request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj})

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Database Views URL Dispatch URL Patterns Template Loader Template Files Models Forms Context Processors

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Views URL Patterns METHOD /path/to/resource/ HTTP/1.1 METHOD /path/to/resource/ HTTP/1.1

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from django.http import HttpResponseNotAllowed def model_detail(request, *args, **kwargs): if request.method == 'GET': request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj}) return HttpResponseNotAllowed(['GET'])

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from django.views.decorators.http import \ require_http_methods @require_http_methods(['GET', 'HEAD']) def model_detail(request, *args, **kwargs): request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj})

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@require_http_methods(['GET', 'HEAD']) def model_detail(request, *args, **kwargs): ... ‑ @require_safe def model_detail(request, *args, **kwargs): ...

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$ ./manage.py runserver $ telnet localhost 8000

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GET /django/ HTTP/1.1 HTTP/1.0 200 OK Date: Wed, 26 Aug 2015 17:38:38 GMT Server: WSGIServer/0.2 CPython/3.4.3 Content-Type: text/html; charset=utf-8 X-Frame-Options: SAMEORIGIN

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OPTIONS /django/ HTTP/1.1 HTTP/1.0 405 METHOD NOT ALLOWED Date: Wed, 26 Aug 2015 17:43:44 GMT Server: WSGIServer/0.2 CPython/3.4.3 Allow: GET, HEAD Content-Type: text/html; charset=utf-8 X-Frame-Options: SAMEORIGIN

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POST /django/ HTTP/1.1 HTTP/1.0 403 FORBIDDEN Date: Wed, 26 Aug 2015 17:41:45 GMT Server: WSGIServer/0.2 CPython/3.4.3 Content-Type: text/html X-Frame-Options: SAMEORIGIN

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url(r'^create/$', views.model_create, name='model_create'),

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def model_create(request, *args, **kwargs): if request.method == 'POST': form = ExampleForm(request.POST) if form.is_valid(): new_obj = form.save() return redirect(new_obj) else: form = ExampleForm() return render( request, 'viewsapp/form.html', {'form': form})

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@require_http_methods(['GET', 'HEAD', 'POST']) def model_create(request, *args, **kwargs): ...

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CLASS-BASED VIEWS AS DRY AS THE SAHARA

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url(r'^(?P[\w\-]+)/$', views.ModelDetail.as_view(), name='model_detail'),

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@require_safe def model_detail(request, *args, **kwargs): request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj})

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def model_detail(request, *args, **kwargs): request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj})

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def get(self, request, *args, **kwargs): request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj})

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class ModelDetail(View): def get(self, request, *args, **kwargs): request_slug = kwargs.get('slug') example_obj = get_object_or_404( ExampleModel, slug=request_slug) return render( request, 'viewsapp/detail.html', {'object': example_obj})

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OPTIONS /django/ HTTP/1.1 HTTP/1.0 200 OK Date: Wed, 26 Aug 2015 17:48:24 GMT Server: WSGIServer/0.2 CPython/3.4.3 Allow: GET, HEAD, OPTIONS X-Frame-Options: SAMEORIGIN Content-Type: text/html; charset=utf-8 Content-Length: 0

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url(r'^create/$', views.ModelCreate.as_view(), name='model_create'),

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class ModelCreate(View): context_object_name = 'form' form_class = ExampleForm template_name = 'viewsapp/form.html' def get(self, request, *args, **kwargs): ... def post(self, request, *args, **kwargs): ...

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class ModelCreate(View): def get(self, request, *args, **kwargs): return render( request, self.template_name, {self.context_object_name: self.form_class()})

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class ModelCreate(View): def post(self, request, *args, **kwargs): bound_form = self.form_class(request.POST) if bound_form.is_valid(): new_obj = bound_form.save() return redirect(new_obj) return render( request, self.template_name, {self.context_object_name: bound_form})

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@require_http_methods(['GET', 'HEAD', 'POST']) def model_create(request, *args, **kwargs): if request.method == 'POST': form = ExampleForm(request.POST) if form.is_valid(): new_obj = form.save() return redirect(new_obj) else: form = ExampleForm() return render( request, 'viewsapp/form.html', {'form': form})

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class ModelCreate(View): def get(self, request, *args, **kwargs): # show form def post(self, request, *args, **kwargs): # show form if error # use data if valid

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GENERIC CLASS-BASED VIEWS OH FOR THE LOVE OF GRAPH THEORY

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from django.views.generic import DetailView, View class ModelDetail(DetailView): model = ExampleModel template_name = 'viewsapp/detail.html'

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from django.views.generic import ( CreateView, DetailView) class ModelCreate(CreateView): context_object_name = 'form' form_class = ExampleForm template_name = 'viewsapp/form.html'

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The Problem put(*args, **kwargs) The PUT action is also handled and just passes all parameters through to post(). https://docs.djangoproject.com/en/1.8/ref/class-based-views/mixins-editing/ #django.views.generic.edit.ProcessFormView.put

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https://ccbv.co.uk

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Stick to the basics display a list of objects display a single object create a single object update a single object delete a single object

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ENHANCE! MAKING VIEWS EASIER

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Classy Class Based Views http://ccbv.co.uk

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django-decorator-plus

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from decorator_plus import ( require_form_methods, require_safe_methods) @require_safe_methods def model_detail(request, *args, **kwargs): ... @require_form_methods def model_create(request, *args, **kwargs): ...

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from decorator_plus import require_http_methods @require_http_methods(['GET']) def model_detail(request, *args, **kwargs): ... @require_http_methods(['GET', 'POST']) def model_create(request, *args, **kwargs): ...

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@require_safe_methods @require_http_methods(['GET']) @require_form_methods @require_http_methods(['GET', 'POST']) HEAD && OPTIONS Included

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IN CONCLUSION ONE SIZE FITS NO-ONE

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Answers: Django handles HTTP for me! Why do I have to worry about it? When is Django deprecating function views? Aren’t all class-based views generic? How do I choose what kind of view to use?

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The Questions Does a generic view do what I want (or almost)? If so, use a generic (and https://ccbv.co.uk). Do I need to inherit/share behavior with another view? If so, use a CBV. If not, then it doesn’t matter.

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Key Take-Aways The view is Django’s solution to HTTP methods All views are callables require_http_methods() should be used with function views Generic Class-Based Views (GCBV) are pre- programmed Class-Based Views (CBV), and are separate concepts with diﬀerent uses

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Thank you! Related Materials: afrg.co/views Django Unleashed: afrg.com/dju Django Class: afrg.co/class @andrewsforge