Django入门笔记【四】

入门笔记翻译整理自：https://docs.djangoproject.com/en/1.8/

*该笔记将使用一个关于投票网络应用（poll application）的例子来阐述Django的用法。

表单和通用视图（Forms&Generic Views）

1. 简单的表单

修改detail.html中的代码，使之含有<form>元素：

 1 # polls/templates/polls/detail.html
 2
 3 <h1>{{ question.question_text }}</h1>
 4
 5 {% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}
 6
 7 <form action="{%url ‘polls:vote‘ question.id %}" method="post">
 8 {% csrf_token %}
 9 {% for choice in question.choice_set.all %}
10     <input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{choice.id }}" />
11     <label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br />
12 {% endfor %}
13 <input type="submit" value="Vote" />
14 </form>

以上代码：首先，为选项生成了radio按钮；其次，当你创建数据服务端（data server-side）的表单时，要始终使用method="post"；然后，forloop.counter对循环进行计数；最后，由于使用了POST方法，我们需要关心跨站请求伪造（Cross Site Request Forgeries），不过Django提供了对此的保护机制。

我们在入门基础【三】中创建了如下代码：

1 # polls/urls.py
2
3 url(r‘^(?P<question_id>[0-9]+/vote/$‘, views.vote, name=‘vote‘),

向polls/views.py中添加如下代码：

 1 # polls/views.py
 2
 3 from django.shortcuts import get_object_or_404, render
 4 from django.http import HttpResponseRedirect, HttpResponse
 5 from django.core.urlresolvers import reverse
 6
 7 from .models import Choice, Question
 8 # ...
 9 def vote(request, question_id):
10     p = get_object_or_404(Question, pk=question_id)
11     try:
12         selected_choice = p.choice_set.get(pk=request.POST[‘choice‘])
13     except (KeyError, Choice.DoesNotExist):
14         # Redisplay the question voting form.
15         return render(request, ‘polls/detail.html‘,{
16             ‘question‘: p,
17             ‘‘error_message‘: "You didn‘t select a choice.",
18     })
19     else:
20         selected_choice.vote += 1
21         selected_choice.save()
22         # Always return an HttpResponseRedirect after successfully dealing
23         # with POST data. This prevents data from being posted twice if a
24         # user hits the Back button.
25         return HttpResponseRedirect(reverse(‘polls:results‘, args=(p.id,)))

当有人在问题下投票后，vote()视图会重新定向至结果页面，该页面视图如下：

1 # polls/views.py
2
3 from django.shortcuts import get_object_or_404, render
4
5 def results(request, question_id):
6     question = get_object_or_404(Question, pk=question_id)
7     return render(request, ‘polls/results.html‘, {‘question‘: question})

现在，创建polls/results.html模板：

 1 # polls/templates/polls/results.html
 2
 3 <h1>{{ question.question_text }}</h1>
 4
 5 <ul>
 6 {% for choice in question.choice_set.all %}
 7     <li>{{ choice.choice_text }} -- {{ choice.votes }} vote {{ choice.votes | pluralize }}</li>
 8 {% endfor %}
 9 </ul>
10
11 <a href="{% url ‘polls:detail‘ question.id %}">Vote again?</a>

2. 使用通用视图

注意到，detail()和results()视图很简单，并且冗余。index()视图也很相似。

这些视图代表了一种常见情形：根据URL中的被传递参数，从数据库中获取数据，载入模板，返回渲染后的模板。对于此类情形，可以使用Django提供的通用视图系统。

为了使用通用视图进行代码简化，我们需要进行以下改变：

1.转换URLconf；2.删除陈旧不必要的视图；3.引入基于通用视图的新视图

3. 修改URLconf

 1 # polls/urls.py
 2
 3 from django.conf.urls import url
 4
 5 from . import views
 6
 7 ulrpatterns = [
 8     url(r‘^$‘, views.IndexView.as_view(), name=‘index‘),
 9     url(r‘^(?P<pk>[0-9]+)/$‘, views.DetailView.as_view(), name=‘detail‘),
10     url(r‘^(?P<pk>[0-9]+)/results/$‘, views.ResultsView.as_view(), name=‘results‘),
11     url(r‘^(?P<question_id>[0-9]+)/vote/$‘, views.vote, name=‘vote‘),
12 ]

注意第二和第三个模式从question_id变成了pk。

4. 修改Views

 1 # polls/views.py
 2
 3 from django.shortcuts import get_object_or_404, render
 4 from django.http import HttpResponseRedirect
 5 from django.core.urlresolvers import reverse
 6 from django.views import generic
 7
 8 from .models import Choice, Question
 9
10 class IndexView(generic.ListView):
11     template_name = ‘polls/index.html‘
12     context_object_name = ‘latest_question_list‘
13
14     def get_queryset(self):
15         """Return the last five published questions."""
16         return Question.objects.order_by(‘-pub_date‘)[:5]
17
18 class DetailView(generic.DetailView):
19     model = Question
20     template_name = ‘polls/detail.html‘
21
22 class ResultsView(generic.DetailView):
23     model = Question
24     template_name = ‘polls/results.html‘
25
26 def vote(request, question_id):
27     ... # same as above

-- The End --