Django通用的基于类的视图示例：** kwargs来自哪里？

问题描述

在这个例子中，我经常看到** kwargs传递，没有提到它来自哪里：

  from django.views.generic import DetailView 
 from books.models import Publisher，Book 
 
 class PublisherDetailView（DetailView）：
 
 context_object_name =publisher
 model = Publisher 
 
 def get_context_data（self，** kwargs）：
＃首先调用基本实现以获取上下文
 context = super（PublisherDetailView，self）.get_context_data（ ** kwargs）
＃添加所有书籍的查询集
上下文['book_list'] = Book.objects.all（）
返回上下文
  

** kwargs是从哪里神奇地拔出来的？

此外，这不是一个额外的工作，只是为了添加一个单一的字典对象？

解决方案

查看 SingleObjectMixin 的基本实现（原始 get_context_data ）。

它只是返回 ** kwargs 作为上下文（一个字典），同时添加正在编辑的对象键指定。

  def get_context_data（self，** kwargs）：
 context = kwargs 
 context_object_name = self.get_context_object_name（self.object）
如果context_object_name：
上下文[context_object_name] = self.object 
返回上下文
  

在 DetailView 中，kwargs从任何调用它/通过这些kwargs的神奇地采摘。在你的情况下，这将是 BaseDetailView.get（）。

  class BaseDetailView（SingleObjectMixin，View）：
 def get（self，request，** kwargs）：
 self.object = self.get_object（）
 context = self.get_context_data（object = self .object）
 return self.render_to_response（context）
  

它被许多视图类使用（如 render_to_response（self.get_context_data）），它将原始上下文字典传递给 self .response_class 这是默认情况下 django.template.TemplateResponse 。

TemplateResponse 知道如何渲染自己，在其 resolve_context 函数中，最后将字典转换为 django。 template.Context

你真的可以从原始方法一直跟随源。

In the examples, I constantly see **kwargs passed around with no mention of where it is coming from:

from django.views.generic import DetailView
from books.models import Publisher, Book

class PublisherDetailView(DetailView):

    context_object_name = "publisher"
    model = Publisher

    def get_context_data(self, **kwargs):
        # Call the base implementation first to get a context
        context = super(PublisherDetailView, self).get_context_data(**kwargs)
        # Add in a QuerySet of all the books
        context['book_list'] = Book.objects.all()
        return context

Where is **kwargs being magically plucked from?

Also, does this not seem like a whole lot of extra work just to add a single dictionary object?

解决方案

Look at the base implementation of SingleObjectMixin (the "original" get_context_data).

It simply returns **kwargs as the context (a dictionary), while adding the object being edited with the key specified.

 def get_context_data(self, **kwargs):
            context = kwargs
            context_object_name = self.get_context_object_name(self.object)
            if context_object_name:
                context[context_object_name] = self.object
            return context

In a DetailView, the kwargs are "magically plucked" from whatever is calling it / passing in those kwargs. In your case, that would be BaseDetailView.get().

class BaseDetailView(SingleObjectMixin, View):
        def get(self, request, **kwargs):
            self.object = self.get_object()
            context = self.get_context_data(object=self.object)
            return self.render_to_response(context)

It's later used by many view classes (as in render_to_response(self.get_context_data)) which passes the raw context dictionary to self.response_class which is by default django.template.TemplateResponse.

TemplateResponse knows how to render itself, and in its resolve_context function, finally converts the dictionary to a django.template.Context

You really can follow the source all the way from the original method all the way down.

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