Form

• 如果是从服务器获取信息，使用 GET；如果是要从服务器修改信息，使用 POST;发生敏感信息，使用 POST
• 上传文件，需要在 form 添加属性 enctype="multipart/form-data"

HTML Form

# polls/templates/polls/detail.html

<h1>{{ question.question_text }}</h1>

{% if error_message %}<p style="color: red;"><strong>{{ error_message }}<strong></p>{% endif %}
    <form action="{% url 'polls:vote' question.id %}" method="post">
    {% csrf_token %} <!-- 防御跨站请求伪造，每个POST action指向同一个网站时必须包含 -->
    {% for choice in question.choice_set.all %}
    <input type="radio" id="choice{{ forloop.counter }}" name="choice" value="{{ choice.id }}" />
    <label for="choice{{ forloop.counter }}">{{choice.choice_text}}</label>
    {% endfor %}
    <br />
    <br />
    <input type="submit" />
</form>

---

处理投票的视图

# polls/views.py
def vote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    try:
        selected_choice = get_object_or_404(Choice, pk=request.POST['choice']) # 类似字典，POST的值都是字符串
    except (KeyError, Choice.DoesNotExist):
        # KeyError: 当 POST 中不存在 choice
        error_message = 'Please select a choice!'
        context = {'question': question, 'error_message': error_message}
        return render(request, 'polls/detail.html', context)
    else:
        selected_choice.vote += 1
        selected_choice.save()
        return HttpResponseRedirect(reverse('polls:result', args=(question_id, )))
        # 每次成功处理 POST后都要进行重定向，避免用户点击 "后退" 时重复提交

def result(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/result.html', {'question': question})

投票加一的处理逻辑有一点问题：当两个用户同时投票，取得值 42，同时加一，保存到数据库的值会时43（正确应是 44）
【解决方法：Avoiding race conditions using F()】

---

# polls/templates/polls/result.html

<h1>{{ question.question_text }}</h1>

<ul>
    {% for choice in question.choice_set.all %}
        <li>{{ choice.choice_text }} -- {{ choice.vote }}</li>
    {% endfor %}
</ul>

投票结果的模板

# polls/templates/polls/result.html

<h1>{{ question.question_text }}</h1>

<ul>
    {% for choice in question.choice_set.all %}
        <li>{{ choice.choice_text }} -- {{ choice.vote }} vote{{ choice.vote|pluralize }}</li>
    {% endfor %}
</ul>

request and response documentation.

通用视图

开发Web通常会：根据URL从数据库获取数据，然后再渲染模板。
Django 提供了通用视图 generic 来简化步骤

修改 URL Pattern

# polls/urls.py
urlpatterns = [
    path('', views.IndexView.as_view(), name='index'),
    path('<int:pk>/', views.DetailView.as_view(), name='detail'),
    path('<int:pk>/result/', views.ResultView.as_view(), name='result'),
    path('<int:question_id>/vote/', views.vote, name='vote'),
]

---

使用通用视图

from django.views import generic
from .models import Question, Choice

class IndexView(generic.ListView):
    template_name = 'polls/index.html'
    context_object_name = 'latest_question_list'

    def get_queryset(self):
        return Question.objects.order_by('-pub_date')[:5]

class DetailView(generic.DetailView):
    model = Question
    template_name = 'polls/detail.html'

class ResultView(generic.DetailView):
    model = Question
    template_name = 'polls/result.html'

---

分类

• ListView: display a list of objects
• DetailView: display a detail page for a particular type of object.

---

• 每个通用视图都需要一个 model 变量
• DetailView 需要从URL中获得 pk (primary key)

默认模板

• ListView: <app name>/<model name>_list.html
• DetailVew: <app name>/<model name>_detail.html
  可以通过变量 template_name 修改

默认 context

默认传递给模板的环境变量名

• ListView: <model name>_list (小写的model name)
• DetailView: <model name> (小写)
  可以通过变量 context_object_name attribute 修改

generic views documentation.