Changes between Version 6 and Version 7 of DjangoDocumentKoreanTranslation/tutorial03


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Timestamp:
01/29/2010 11:44:23 PM (5 years ago)
Author:
sangho
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  • DjangoDocumentKoreanTranslation/tutorial03

    v6 v7  
    1 .. _intro-tutorial03:
    2 
    3 =====================================
    4 세번째 : views 작성하기
    5 =====================================
    6 
    7 이 페이지는 "views"라는 public interface에 대해 중점을 두고 Web-poll 어플리케이션을 다룹니다.
    8 
    9 개념
    10 ==========
    11 뷰(view)는 장고 어플리케이션에서 구체적인 기능을 수행하고, 특정한 템플릿을 가지고 있기도 한 웹페이지의 "형태"중 한가지 입니다. 예를들어, 만약 당신이 블로그 어플리케이션을 만든다면, 아래와 같은 뷰를 사용해야 할 것입니다.
    12 
    13     * 블로그 홈페이지 -- 최근에 올라온 글 몇개를 보여줍니다.
    14 
    15     * 글 "자세히" 페이지 -- 한 개의 글에 대한 바로 가기 페이지
    16 
    17     * 1년 기준 문서 페이지 -- 1년 동안의 모든 글을 보여줍니다.
    18 
    19     * 한달 기준 문서 페이지 -- 한달 동안의 모든 글을 보여줍니다.
    20 
    21     * 하루 기준 문서 페이지 -- 하루 동안의 모든 글을 보여줍니다.
    22 
    23     * 댓글 처리 -- 글에 대한 댓글을 작성하는 작업을 합니다.
    24 
    25 
    26 우리의 poll 어플리케이션에서는 아래의 네가지 뷰를 쓸 것 입니다.
    27 
    28     * Poll "문서" 페이지 -- 최근 몇개의 poll들을 보여줍니다.
    29 
    30     * Poll "자세히" 페이지 -- poll의 제목과, 투표를 하기위한 폼을 보여줍니다. (결과는 없음)
    31 
    32     * Poll "결과" 페이지 -- 특정한 poll의 결과를 보여줍니다.
    33 
    34     * 투표 처리 -- 특정한 poll에 대한 특정한 선택에 대한 투표를 처리합니다.
    35 
    36 장고에서 각각의 뷰는 간단한 파이썬 함수로 만들 수 있습니다.
    37 
    38 
    39 URL 디자인 하기
    40 ================
    41 뷰를 작성하기 위한 첫 번째 단계는 URLconf라는 파이썬 모듈을 작성해서 URL 구조를 설계하는 것입니다.
    42 URLconf는 특정 URL을 그에 주어진 파이썬 코드로 연결시킵니다.
    43 
    44 유저가 장고기반 페이지를 요청하면 시스템은 Python dotted 문법의 문자열을 포함한 :setting:`ROOT_URLCONF` 세팅을 불러들이고,
    45 아래와 같은 튜플 형태인 ``urlpatterns`` 라는 모듈레벨의 변수를 찾습니다.::
    46 
    47     (정규표현식, 파이썬 콜백 함수, [, 부가적인 사전자료형])
    48 
    49 장고는 요청된 URL을 나타내는 정규표현식이 나올 때 까지 첫 번째 정규표현식부터 아래로 쭉 훑습니다.
    50 
    51 적합한 정규표현식을 찾았다면, 장고는 :class:`~django.http.HttpRequest`를 첫번째 인자로 하는 파이썬 콜백 함수를 호출합니다.
    52 정규표현식에 의해 "걸려진" 값들도 키워드 인자로 전달되고, 위의 사전자료형 (세번째로 받은 튜플값)에서도 인자가 전달됩니다.
    53 
    54 :class:`~django.http.HttpRequest`에 대한 더 많은정보는 :ref:`ref-request-response`이곳에서, URLconfs에 관한 정보는 :ref:`topics-http-urls`이 곳을 참고 하세요
    55 
    56 만약 여러분이 튜토리얼1 에서 ``django-admin.py startproject mysite`` 커맨드를 실행하셨다면 URLconf가 ``mysite/urls.py``에 기본적으로 생겼을 것이고,
    57 :setting:`ROOT_URLCONF`세팅또한 ``setting.py``에 생겼을 것입니다.::
    58 
    59     ROOT_URLCONF = 'mysite.urls'
    60 
    61 이제 예를들기위해 ``mysite/urls.py`` 를 수정해보겠습니다. 대략 아래와 같이 생겼습니다::
    62 
    63     from django.conf.urls.defaults import *
    64 
    65     from django.contrib import admin
    66     admin.autodiscover()
    67 
    68     urlpatterns = patterns('',
    69         (r'^polls/$', 'mysite.polls.views.index'),
    70         (r'^polls/(?P<poll_id>\d+)/$', 'mysite.polls.views.detail'),
    71         (r'^polls/(?P<poll_id>\d+)/results/$', 'mysite.polls.views.results'),
    72         (r'^polls/(?P<poll_id>\d+)/vote/$', 'mysite.polls.views.vote'),
    73         (r'^admin/', include(admin.site.urls)),
    74     )
    75 
    76 This is worth a review. When somebody requests a page from your Web site -- say,
    77 "/polls/23/", Django will load this Python module, because it's pointed to by
    78 the :setting:`ROOT_URLCONF` setting. It finds the variable named ``urlpatterns``
    79 and traverses the regular expressions in order. When it finds a regular
    80 expression that matches -- ``r'^polls/(?P<poll_id>\d+)/$'`` -- it loads the
    81 function ``detail()`` from ``mysite/polls/views.py``. Finally,
    82 it calls that ``detail()`` function like so::
    83 
    84 
    85     detail(request=<HttpRequest object>, poll_id='23')
    86 
    87 The ``poll_id='23'`` part comes from ``(?P<poll_id>\d+)``. Using parenthesis
    88 around a pattern "captures" the text matched by that pattern and sends it as an
    89 argument to the view function; the ``?P<poll_id>`` defines the name that will be
    90 used to identify the matched pattern; and ``\d+`` is a regular expression to
    91 match a sequence of digits (i.e., a number).
    92 
    93 Because the URL patterns are regular expressions, there really is no limit on
    94 what you can do with them. And there's no need to add URL cruft such as ``.php``
    95 -- unless you have a sick sense of humor, in which case you can do something
    96 like this::
    97 
    98     (r'^polls/latest\.php$', 'mysite.polls.views.index'),
    99 
    100 But, don't do that. It's silly.
    101 
    102 Note that these regular expressions do not search GET and POST parameters, or
    103 the domain name. For example, in a request to ``http://www.example.com/myapp/``,
    104 the URLconf will look for ``myapp/``. In a request to
    105 ``http://www.example.com/myapp/?page=3``, the URLconf will look for ``myapp/``.
    106 
    107 If you need help with regular expressions, see `Wikipedia's entry`_ and the
    108 `Python documentation`_. Also, the O'Reilly book "Mastering Regular Expressions"
    109 by Jeffrey Friedl is fantastic.
    110 
    111 Finally, a performance note: these regular expressions are compiled the first
    112 time the URLconf module is loaded. They're super fast.
    113 
    114 .. _Wikipedia's entry: http://en.wikipedia.org/wiki/Regular_expression
    115 .. _Python documentation: http://docs.python.org/library/re.html
    116 
    117 Write your first view
    118 =====================
    119 
    120 Well, we haven't created any views yet -- we just have the URLconf. But let's
    121 make sure Django is following the URLconf properly.
    122 
    123 Fire up the Django development Web server:
    124 
    125 .. code-block:: bash
    126 
    127     python manage.py runserver
    128 
    129 Now go to "http://localhost:8000/polls/" on your domain in your Web browser.
    130 You should get a pleasantly-colored error page with the following message::
    131 
    132     ViewDoesNotExist at /polls/
    133 
    134     Tried index in module mysite.polls.views. Error was: 'module'
    135     object has no attribute 'index'
    136 
    137 This error happened because you haven't written a function ``index()`` in the
    138 module ``mysite/polls/views.py``.
    139 
    140 Try "/polls/23/", "/polls/23/results/" and "/polls/23/vote/". The error
    141 messages tell you which view Django tried (and failed to find, because you
    142 haven't written any views yet).
    143 
    144 Time to write the first view. Open the file ``mysite/polls/views.py``
    145 and put the following Python code in it::
    146 
    147     from django.http import HttpResponse
    148 
    149     def index(request):
    150         return HttpResponse("Hello, world. You're at the poll index.")
    151 
    152 This is the simplest view possible. Go to "/polls/" in your browser, and you
    153 should see your text.
    154 
    155 Now lets add a few more views. These views are slightly different, because
    156 they take an argument (which, remember, is passed in from whatever was
    157 captured by the regular expression in the URLconf)::
    158 
    159     def detail(request, poll_id):
    160         return HttpResponse("You're looking at poll %s." % poll_id)
    161 
    162     def results(request, poll_id):
    163         return HttpResponse("You're looking at the results of poll %s." % poll_id)
    164 
    165     def vote(request, poll_id):
    166         return HttpResponse("You're voting on poll %s." % poll_id)
    167 
    168 Take a look in your browser, at "/polls/34/". It'll run the `detail()` method
    169 and display whatever ID you provide in the URL. Try "/polls/34/results/" and
    170 "/polls/34/vote/" too -- these will display the placeholder results and voting
    171 pages.
    172 
    173 Write views that actually do something
    174 ======================================
    175 
    176 Each view is responsible for doing one of two things: Returning an
    177 :class:`~django.http.HttpResponse` object containing the content for the
    178 requested page, or raising an exception such as :exc:`~django.http.Http404`. The
    179 rest is up to you.
    180 
    181 Your view can read records from a database, or not. It can use a template
    182 system such as Django's -- or a third-party Python template system -- or not.
    183 It can generate a PDF file, output XML, create a ZIP file on the fly, anything
    184 you want, using whatever Python libraries you want.
    185 
    186 All Django wants is that :class:`~django.http.HttpResponse`. Or an exception.
    187 
    188 Because it's convenient, let's use Django's own database API, which we covered
    189 in :ref:`Tutorial 1 <intro-tutorial01>`. Here's one stab at the ``index()``
    190 view, which displays the latest 5 poll questions in the system, separated by
    191 commas, according to publication date::
    192 
    193     from mysite.polls.models import Poll
    194     from django.http import HttpResponse
    195 
    196     def index(request):
    197         latest_poll_list = Poll.objects.all().order_by('-pub_date')[:5]
    198         output = ', '.join([p.question for p in latest_poll_list])
    199         return HttpResponse(output)
    200 
    201 There's a problem here, though: The page's design is hard-coded in the view. If
    202 you want to change the way the page looks, you'll have to edit this Python code.
    203 So let's use Django's template system to separate the design from Python::
    204 
    205     from django.template import Context, loader
    206     from mysite.polls.models import Poll
    207     from django.http import HttpResponse
    208 
    209     def index(request):
    210         latest_poll_list = Poll.objects.all().order_by('-pub_date')[:5]
    211         t = loader.get_template('polls/index.html')
    212         c = Context({
    213             'latest_poll_list': latest_poll_list,
    214         })
    215         return HttpResponse(t.render(c))
    216 
    217 That code loads the template called "polls/index.html" and passes it a context.
    218 The context is a dictionary mapping template variable names to Python objects.
    219 
    220 Reload the page. Now you'll see an error::
    221 
    222     TemplateDoesNotExist at /polls/
    223     polls/index.html
    224 
    225 Ah. There's no template yet. First, create a directory, somewhere on your
    226 filesystem, whose contents Django can access. (Django runs as whatever user your
    227 server runs.) Don't put them under your document root, though. You probably
    228 shouldn't make them public, just for security's sake.
    229 Then edit :setting:`TEMPLATE_DIRS` in your ``settings.py`` to tell Django where
    230 it can find templates -- just as you did in the "Customize the admin look and
    231 feel" section of Tutorial 2.
    232 
    233 When you've done that, create a directory ``polls`` in your template directory.
    234 Within that, create a file called ``index.html``. Note that our
    235 ``loader.get_template('polls/index.html')`` code from above maps to
    236 "[template_directory]/polls/index.html" on the filesystem.
    237 
    238 Put the following code in that template:
    239 
    240 .. code-block:: html+django
    241 
    242     {% if latest_poll_list %}
    243         <ul>
    244         {% for poll in latest_poll_list %}
    245             <li>{{ poll.question }}</li>
    246         {% endfor %}
    247         </ul>
    248     {% else %}
    249         <p>No polls are available.</p>
    250     {% endif %}
    251 
    252 Load the page in your Web browser, and you should see a bulleted-list
    253 containing the "What's up" poll from Tutorial 1.
    254 
    255 A shortcut: render_to_response()
    256 --------------------------------
    257 
    258 It's a very common idiom to load a template, fill a context and return an
    259 :class:`~django.http.HttpResponse` object with the result of the rendered
    260 template. Django provides a shortcut. Here's the full ``index()`` view,
    261 rewritten::
    262 
    263     from django.shortcuts import render_to_response
    264     from mysite.polls.models import Poll
    265 
    266     def index(request):
    267         latest_poll_list = Poll.objects.all().order_by('-pub_date')[:5]
    268         return render_to_response('polls/index.html', {'latest_poll_list': latest_poll_list})
    269 
    270 Note that once we've done this in all these views, we no longer need to import
    271 :mod:`~django.template.loader`, :class:`~django.template.Context` and
    272 :class:`~django.http.HttpResponse`.
    273 
    274 The :func:`~django.shortcuts.render_to_response` function takes a template name
    275 as its first argument and a dictionary as its optional second argument. It
    276 returns an :class:`~django.http.HttpResponse` object of the given template
    277 rendered with the given context.
    278 
    279 Raising 404
    280 ===========
    281 
    282 Now, let's tackle the poll detail view -- the page that displays the question
    283 for a given poll. Here's the view::
    284 
    285     from django.http import Http404
    286     # ...
    287     def detail(request, poll_id):
    288         try:
    289             p = Poll.objects.get(pk=poll_id)
    290         except Poll.DoesNotExist:
    291             raise Http404
    292         return render_to_response('polls/detail.html', {'poll': p})
    293 
    294 The new concept here: The view raises the :exc:`~django.http.Http404` exception
    295 if a poll with the requested ID doesn't exist.
    296 
    297 We'll discuss what you could put in that ``polls/detail.html`` template a bit
    298 later, but if you'd like to quickly get the above example working, just::
    299 
    300     {{ poll }}
    301 
    302 will get you started for now.
    303 
    304 A shortcut: get_object_or_404()
    305 -------------------------------
    306 
    307 It's a very common idiom to use :meth:`~django.db.models.QuerySet.get` and raise
    308 :exc:`~django.http.Http404` if the object doesn't exist. Django provides a
    309 shortcut. Here's the ``detail()`` view, rewritten::
    310 
    311     from django.shortcuts import render_to_response, get_object_or_404
    312     # ...
    313     def detail(request, poll_id):
    314         p = get_object_or_404(Poll, pk=poll_id)
    315         return render_to_response('polls/detail.html', {'poll': p})
    316 
    317 The :func:`~django.shortcuts.get_object_or_404` function takes a Django model
    318 as its first argument and an arbitrary number of keyword arguments, which it
    319 passes to the module's :meth:`~django.db.models.QuerySet.get` function. It
    320 raises :exc:`~django.http.Http404` if the object doesn't exist.
    321 
    322 .. admonition:: Philosophy
    323 
    324     Why do we use a helper function :func:`~django.shortcuts.get_object_or_404`
    325     instead of automatically catching the
    326     :exc:`~django.core.exceptions.ObjectDoesNotExist` exceptions at a higher
    327     level, or having the model API raise :exc:`~django.http.Http404` instead of
    328     :exc:`~django.core.exceptions.ObjectDoesNotExist`?
    329 
    330     Because that would couple the model layer to the view layer. One of the
    331     foremost design goals of Django is to maintain loose coupling.
    332 
    333 There's also a :func:`~django.shortcuts.get_list_or_404` function, which works
    334 just as :func:`~django.shortcuts.get_object_or_404` -- except using
    335 :meth:`~django.db.models.QuerySet.filter` instead of
    336 :meth:`~django.db.models.QuerySet.get`. It raises :exc:`~django.http.Http404` if
    337 the list is empty.
    338 
    339 Write a 404 (page not found) view
    340 =================================
    341 
    342 When you raise :exc:`~django.http.Http404` from within a view, Django will load
    343 a special view devoted to handling 404 errors. It finds it by looking for the
    344 variable ``handler404``, which is a string in Python dotted syntax -- the same
    345 format the normal URLconf callbacks use. A 404 view itself has nothing special:
    346 It's just a normal view.
    347 
    348 You normally won't have to bother with writing 404 views. By default, URLconfs
    349 have the following line up top::
    350 
    351     from django.conf.urls.defaults import *
    352 
    353 That takes care of setting ``handler404`` in the current module. As you can see
    354 in ``django/conf/urls/defaults.py``, ``handler404`` is set to
    355 :func:`django.views.defaults.page_not_found` by default.
    356 
    357 Four more things to note about 404 views:
    358 
    359     * If :setting:`DEBUG` is set to ``True`` (in your settings module) then your
    360       404 view will never be used (and thus the ``404.html`` template will never
    361       be rendered) because the traceback will be displayed instead.
    362 
    363     * The 404 view is also called if Django doesn't find a match after checking
    364       every regular expression in the URLconf.
    365 
    366     * If you don't define your own 404 view -- and simply use the default, which
    367       is recommended -- you still have one obligation: To create a ``404.html``
    368       template in the root of your template directory. The default 404 view will
    369       use that template for all 404 errors.
    370 
    371     * If :setting:`DEBUG` is set to ``False`` (in your settings module) and if
    372       you didn't create a ``404.html`` file, an ``Http500`` is raised instead.
    373       So remember to create a ``404.html``.
    374 
    375 Write a 500 (server error) view
    376 ===============================
    377 
    378 Similarly, URLconfs may define a ``handler500``, which points to a view to call
    379 in case of server errors. Server errors happen when you have runtime errors in
    380 view code.
    381 
    382 Use the template system
    383 =======================
    384 
    385 Back to the ``detail()`` view for our poll application. Given the context
    386 variable ``poll``, here's what the "polls/detail.html" template might look
    387 like:
    388 
    389 .. code-block:: html+django
    390 
    391     <h1>{{ poll.question }}</h1>
    392     <ul>
    393     {% for choice in poll.choice_set.all %}
    394         <li>{{ choice.choice }}</li>
    395     {% endfor %}
    396     </ul>
    397 
    398 The template system uses dot-lookup syntax to access variable attributes. In
    399 the example of ``{{ poll.question }}``, first Django does a dictionary lookup
    400 on the object ``poll``. Failing that, it tries attribute lookup -- which works,
    401 in this case. If attribute lookup had failed, it would've tried calling the
    402 method ``question()`` on the poll object.
    403 
    404 Method-calling happens in the ``{% for %}`` loop: ``poll.choice_set.all`` is
    405 interpreted as the Python code ``poll.choice_set.all()``, which returns an
    406 iterable of Choice objects and is suitable for use in the ``{% for %}`` tag.
    407 
    408 See the :ref:`template guide <topics-templates>` for more about templates.
    409 
    410 Simplifying the URLconfs
    411 ========================
    412 
    413 Take some time to play around with the views and template system. As you edit
    414 the URLconf, you may notice there's a fair bit of redundancy in it::
    415 
    416     urlpatterns = patterns('',
    417         (r'^polls/$', 'mysite.polls.views.index'),
    418         (r'^polls/(?P<poll_id>\d+)/$', 'mysite.polls.views.detail'),
    419         (r'^polls/(?P<poll_id>\d+)/results/$', 'mysite.polls.views.results'),
    420         (r'^polls/(?P<poll_id>\d+)/vote/$', 'mysite.polls.views.vote'),
    421     )
    422 
    423 Namely, ``mysite.polls.views`` is in every callback.
    424 
    425 Because this is a common case, the URLconf framework provides a shortcut for
    426 common prefixes. You can factor out the common prefixes and add them as the
    427 first argument to :func:`~django.conf.urls.defaults.patterns`, like so::
    428 
    429     urlpatterns = patterns('mysite.polls.views',
    430         (r'^polls/$', 'index'),
    431         (r'^polls/(?P<poll_id>\d+)/$', 'detail'),
    432         (r'^polls/(?P<poll_id>\d+)/results/$', 'results'),
    433         (r'^polls/(?P<poll_id>\d+)/vote/$', 'vote'),
    434     )
    435 
    436 This is functionally identical to the previous formatting. It's just a bit
    437 tidier.
    438 
    439 Decoupling the URLconfs
    440 =======================
    441 
    442 While we're at it, we should take the time to decouple our poll-app URLs from
    443 our Django project configuration. Django apps are meant to be pluggable -- that
    444 is, each particular app should be transferable to another Django installation
    445 with minimal fuss.
    446 
    447 Our poll app is pretty decoupled at this point, thanks to the strict directory
    448 structure that ``python manage.py startapp`` created, but one part of it is
    449 coupled to the Django settings: The URLconf.
    450 
    451 We've been editing the URLs in ``mysite/urls.py``, but the URL design of an
    452 app is specific to the app, not to the Django installation -- so let's move the
    453 URLs within the app directory.
    454 
    455 Copy the file ``mysite/urls.py`` to ``mysite/polls/urls.py``. Then, change
    456 ``mysite/urls.py`` to remove the poll-specific URLs and insert an
    457 :func:`~django.conf.urls.defaults.include`::
    458 
    459     # ...
    460     urlpatterns = patterns('',
    461         (r'^polls/', include('mysite.polls.urls')),
    462         # ...
    463 
    464 :func:`~django.conf.urls.defaults.include`, simply, references another URLconf.
    465 Note that the regular expression doesn't have a ``$`` (end-of-string match
    466 character) but has the trailing slash. Whenever Django encounters
    467 :func:`~django.conf.urls.defaults.include`, it chops off whatever part of the
    468 URL matched up to that point and sends the remaining string to the included
    469 URLconf for further processing.
    470 
    471 Here's what happens if a user goes to "/polls/34/" in this system:
    472 
    473     * Django will find the match at ``'^polls/'``
    474 
    475     * Then, Django will strip off the matching text (``"polls/"``) and send the
    476       remaining text -- ``"34/"`` -- to the 'mysite.polls.urls' URLconf for
    477       further processing.
    478 
    479 Now that we've decoupled that, we need to decouple the 'mysite.polls.urls'
    480 URLconf by removing the leading "polls/" from each line, and removing the
    481 lines registering the admin site::
    482 
    483     urlpatterns = patterns('mysite.polls.views',
    484         (r'^$', 'index'),
    485         (r'^(?P<poll_id>\d+)/$', 'detail'),
    486         (r'^(?P<poll_id>\d+)/results/$', 'results'),
    487         (r'^(?P<poll_id>\d+)/vote/$', 'vote'),
    488     )
    489 
    490 The idea behind :func:`~django.conf.urls.defaults.include` and URLconf
    491 decoupling is to make it easy to plug-and-play URLs. Now that polls are in their
    492 own URLconf, they can be placed under "/polls/", or under "/fun_polls/", or
    493 under "/content/polls/", or any other URL root, and the app will still work.
    494 
    495 All the poll app cares about is its relative URLs, not its absolute URLs.
    496 
    497 When you're comfortable with writing views, read :ref:`part 4 of this tutorial
    498 <intro-tutorial04>` to learn about simple form processing and generic views.
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