Django Views: Functions, Classes, and Generics

Presented at DjangoCon US 2015.

At the heart of Django is the HTTP Request and Response cycle, powered by URL patterns and views that you must create. But what kind of view should you use? A view function? A class-based view? A generic class-based view? This talk is all about the essence of views, and will explore the differences, advantages and disadvantages of each type of view, finishing with a guide of when to use what.

http://andrewsforge.com/presentation/django-views-functions-classes-generics/

Transcript

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

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

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3. AUTHOR OF DJANGO UNLEASHED
   AVAILABLE FOR PREORDER; SHIPS DECEMBER 2015
   

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4. 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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5. $ ls views
   1_fundamentals
   
   2_views
   
   3_tools
   

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

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

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

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10. afrg.co/views
    

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11. PYTHON CALLABLES
    UNDERSTANDING THE PROBLEM
    

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

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

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14. 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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15. 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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16. 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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17. >>> 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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18. WHAT IS HTTP, ANYWAY?
    UNDERSTANDING THE PROBLEM
    

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

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21. HyperText Transfer Protocol
    Idempotent Methods
    
    POST
    
    PUT
    

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23. Your website must
    adhere to HTTP
    

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

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25. Your website must
    adhere to HTTP
    

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26. Goal of Software
    Solve a Problem
    
    Automate Behavior
    

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28. Goal of Software
    Solve a Problem
    
    Automate Behavior
    

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

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30. DJANGO’S REQUEST/RESPONSE CYCLE
    UNDERSTANDING THE PROBLEM
    

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

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

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34. Simplification
    No WSGI Server
    
    No View Middleware
    
    No Exception Handling
    

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35. Views
    URL Dispatch
    URL Patterns
    

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

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

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

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39. 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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40. What is a view?
    Any Python Callable
    

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

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

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43. 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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44. Functions are Rigid
    Extend generic views?
    
    Use classes!
    

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45. 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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46. 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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47. Class-Based Views
    Simple (Usable - principle of least surprise)
    
    Extendable
    
    Inheritance
    
    Decorators
    
    Safe (Thread-Safe)
    
    Testable
    

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

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

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

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

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

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

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57. 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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58. Views
    URL Patterns
    METHOD /path/to/resource/ HTTP/1.1
    METHOD /path/to/resource/ HTTP/1.1
    

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59. 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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60. 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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61. @require_http_methods(['GET', 'HEAD'])
    def model_detail(request, *args, **kwargs):
    ...
    ‑
    @require_safe
    def model_detail(request, *args, **kwargs):
    ...
    

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62. $ ./manage.py runserver
    $ telnet localhost 8000
    

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63. 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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64. 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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65. 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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66. url(r'^create/$',
    views.model_create,
    name='model_create'),
    

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67. 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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68. View Slide

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

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70. CLASS-BASED VIEWS
    AS DRY AS THE SAHARA
    

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

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72. @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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73. 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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74. 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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75. 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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76. 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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77. url(r'^create/$',
    views.ModelCreate.as_view(),
    name='model_create'),
    

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78. 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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79. 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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80. 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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81. @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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82. 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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83. GENERIC CLASS-BASED VIEWS
    OH FOR THE LOVE OF GRAPH THEORY
    

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

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85. 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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86. 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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91. View Slide

92. https://ccbv.co.uk
    

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93. 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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94. View Slide

95. ENHANCE!
    MAKING VIEWS EASIER
    

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

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97. View Slide

98. View Slide

99. View Slide

100. View Slide

101. View Slide

102. django-decorator-plus
     

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103. 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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104. 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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105. @require_safe_methods
     @require_http_methods(['GET'])
     @require_form_methods
     @require_http_methods(['GET', 'POST'])
     HEAD && OPTIONS
     Included
     

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106. IN CONCLUSION
     ONE SIZE FITS NO-ONE
     

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107. 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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108. 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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109. 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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110. Thank you!
     Related Materials: afrg.co/views
     Django Unleashed: afrg.com/dju
     Django Class: afrg.co/class
     @andrewsforge
     

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