4.2 use generic views

first_django_app.md

@@ -326,3 +326,94 @@ def results(request, question_id):
 
 <a href="{% url 'polls:detail' question.id %}">Vote again?</a>
 ```
+
+### 4.2 使用通用视图(generic views)：代码还是少点好
+
+Web 开发中的一个常见情况：根据 URL 中的参数从数据库中获取数据、载入模板文件然后返回渲染后的模板。 由于这种情况特别常见，Django 提供一种快捷方式，叫做“通用视图”系统。
+
+让我们将我们的投票应用转换成使用通用视图系统，这样我们可以删除许多我们的代码。我们仅仅需要做以下几步来完成转换，我们将：
+
+* 转换 URLconf。
+* 删除一些旧的、不再需要的视图。
+* 基于 Django 的通用视图引入新的视图。
+
+
+#### Modify URLconf of polls
+
+Change 
+
+```python
+    # ex: /polls/
+    path('', views.index, name='index'),
+    # ex: /polls/5/
+    path('<int:question_id>/', views.detail, name='detail'),
+    # ex: /polls/5/results/
+    path('<int:question_id>/results/', views.results, name='results'),
+```
+
+to
+
+```python
+    path('', views.IndexView.as_view(), name='index'),
+    path('<int:pk>/', views.DetailView.as_view(), name='detail'),
+    path('<int:pk>/results/', views.ResultsView.as_view(), name='results'),
+```
+
+* 注意，第二个和第三个匹配准则中，路径字符串中匹配模式的名称已经由 <question_id> 改为 <pk> (primary key)。
+
+#### Modify Views
+
+Target: Replace `index`, `details` & `results` views using Django's generic views that named in `polls/urls.py`
+
+将
+
+```python
+def index(request):
+    latest_question_list = Question.objects.order_by('-pub_date')[:5]
+    context = {'latest_question_list': latest_question_list}
+    return render(request, 'polls/index.html', context)
+
+def detail(request, question_id):
+    question = get_object_or_404(Question, pk=question_id)
+    return render(request, 'polls/detail.html', {'question': question})
+
+def results(request, question_id):
+    question = get_object_or_404(Question, pk=question_id)
+    return render(request, 'polls/results.html', {'question': question})
+```
+
+改为
+
+```python
+class IndexView(generic.ListView):
+    template_name = 'polls/index.html'
+    context_object_name = 'latest_question_list'
+
+    def get_queryset(self):
+        """Return the last five published questions."""
+        return Question.objects.order_by('-pub_date')[:5]
+
+class DetailView(generic.DetailView):
+    model = Question
+    template_name = 'polls/detail.html'
+
+class ResultsView(generic.DetailView):
+    model = Question
+    template_name = 'polls/results.html'
+```
+
+两个通用视图： ListView 和 DetailView 。这两个视图分别抽象“显示一个对象列表”和“显示一个特定类型对象的详细信息页面”这两种概念。
+* 每个通用视图需要知道它将作用于哪个模型。 这由 model 属性 (i.e. model members) 提供。
+* DetailView 期望从 URL 中捕获名为 "pk" 的主键值，所以我们为通用视图把 question_id 改成 pk 。
+
+解释 DetailView
+* 默认情况下，通用视图 DetailView 使用一个叫做 <app name>/<model name>_detail.html 的模板。
+  * e.g. "polls/question_detail.html" template for us.
+* 但是我们可以用 model member `template_name` 来指定模板
+
+解释 ListView
+* ListView 也使用一个叫做 <app name>/<model name>_list.html 的默认模板
+* 而这里我们使用 `template_name` 来指定模板
+* 我们提供 context_object_name 属性，表示我们想使用 latest_question_list
+
+重启服务器后，就是新的投票应用（同样的html），但是内部用了generic view

src/polls/urls.py

@@ -5,11 +5,11 @@ from . import views
 app_name = 'polls'
 urlpatterns = [
     # ex: /polls/
-    path('', views.index, name='index'),
+    path('', views.IndexView.as_view(), name='index'),
     # ex: /polls/5/
-    path('<int:question_id>/', views.detail, name='detail'),
+    path('<int:pk>/', views.DetailView.as_view(), name='detail'),
     # ex: /polls/5/results/
-    path('<int:question_id>/results/', views.results, name='results'),
+    path('<int:pk>/results/', views.ResultsView.as_view(), name='results'),
     # ex: /polls/5/vote/
     path('<int:question_id>/vote/', views.vote, name='vote'),
 ]

src/polls/views.py

@@ -2,21 +2,25 @@ from django.http import request, HttpResponse, HttpResponseRedirect
 from django.shortcuts import render, get_object_or_404
 from django.template import loader
 from django.urls import reverse
+from django.views import generic
 
 from .models import Question, Choice
 
-def index(request):
-    latest_question_list = Question.objects.order_by('-pub_date')[:5]
-    context = {'latest_question_list': latest_question_list}
-    return render(request, 'polls/index.html', context)
+class IndexView(generic.ListView):
+    template_name = 'polls/index.html'
+    context_object_name = 'latest_question_list'
 
-def detail(request, question_id):
-    question = get_object_or_404(Question, pk=question_id)
-    return render(request, 'polls/detail.html', {'question': question})
+    def get_queryset(self):
+        """Return the last five published questions."""
+        return Question.objects.order_by('-pub_date')[:5]
 
-def results(request, question_id):
-    question = get_object_or_404(Question, pk=question_id)
-    return render(request, 'polls/results.html', {'question': question})
+class DetailView(generic.DetailView):
+    model = Question
+    template_name = 'polls/detail.html'
+
+class ResultsView(generic.DetailView):
+    model = Question
+    template_name = 'polls/results.html'
 
 def vote(request, question_id):
     question = get_object_or_404(Question, pk=question_id)