Django View Types

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Django View Types

Basic information

  • Django version: 2.1

Introduction

當一個 HTTP request被WSGI server接收時，在WSGIHandler中會根據url.py配置，找到對應的view function
相應代碼在WSGIHandler父類BaseHandler @django/core/handlers/base.py

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class BaseHandler:
    def _get_response(self, request):
        # ...
        resolver_match = resolver.resolve(request.path_info)
        callback, callback_args, callback_kwargs = resolver_match
        request.resolver_match = resolver_match
        # ...
        if response is None:
            wrapped_callback = self.make_view_atomic(callback)
            try:
                response = wrapped_callback(request, *callback_args, **callback_kwargs)
            except Exception as e:
                response = self.process_exception_by_middleware(e, request)

wrapped_callback就是View function，上述可知，View function是一個接收三個參數的function

Django View Types

Django常用的view可以分為以下兩類

  • FBV(Function Based View)

    • 優點
      • 寫法容易，容易理解
      • 可以直接使用Decorator
    • 缺點
      • 不便於繼承與重用
      • 處理HTTP methods時，需要在內部使用條件判斷處理

    • 示例

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      path("", index)
      def index(request):
          return HttpResponse("It is the index page")

  • CBV(Class Based View)

    • Django提供許多Built-in class-based views，分成以下兩類
      • Base views
        • 提供最基本的常用功能，可以直接使用或者繼承後使用
        • Generic views的父類
      • Generic views
        • 提供常用的功能，例如數據展現或修改頁面
        • 常用功能與對應Generic views如下:
          • Display views
            • ListView: 展現數據列表
            • DetailView: 展現特定數據的詳細資料
          • Edit views
            • FormView: 用戶填寫Form後轉跳到對應頁面
            • CreateView: 透過Form創建某項數據
            • UpdateView: 更改數據資料
            • DeleteView: 刪除數據
          • Generic date views
            • ArchiveIndexView: 從最近日期開始顯示數據列表
            • YearArchiveView: 根據年過濾顯示數據列表
            • MonthArchiveView: 根據年/月過濾顯示數據列表
            • WeekArchiveView: 根據年/週過濾顯示數據列表
            • DayArchiveView: 根據年/月/日過濾顯示數據列表
            • TodayArchiveView: 根據今日過濾顯示數據列表
            • DateDetailView: 顯示特定日期數據的詳細資料
    • 可以搭配Class-based views mixins使用
    • 上述提到View function只能是一個接收三個參數的function，Django在所有View的父類View @django/views/generic/base.py 提供一個as_view方法，可將CBV轉換成View function

    • 當WSGIHandler的調用View function時，as_view內部會呼叫自身的dispatch，dispatch會根據http method調用View所實作對應名稱的function

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      class View:
          @classonlymethod
          def as_view(cls, **initkwargs):
              # ...
              def view(request, *args, **kwargs):
                  print("[View] cls to init object")
                  self = cls(**initkwargs)
                  if hasattr(self, 'get') and not hasattr(self, 'head'):
                      self.head = self.get
                  self.setup(request, *args, **kwargs)
                  if not hasattr(self, 'request'):
                      raise AttributeError(
                          "%s instance has no 'request' attribute. Did you override "
                          "setup() and forget to call super()?" % cls.__name__
                      )
                  return self.dispatch(request, *args, **kwargs)
              # ...
              return view
          def dispatch(self, request, *args, **kwargs):
              # Try to dispatch to the right method; if a method doesn't exist,
              # defer to the error handler. Also defer to the error handler if the
              # request method isn't on the approved list.
              if request.method.lower() in self.http_method_names:
                  handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
              else:
                  handler = self.http_method_not_allowed
              return handler(request, *args, **kwargs)

    • 示例

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      path("", IndexView.as_view())
      class IndexView(View):
          def get(self, request, *args, **kwarg):
              return HttpResponese("It is the index page")