使用get_queryset（）方法还是设置queryset变量？ [英] Use get_queryset() method or set queryset variable?

问题描述

这两个代码在第一次出现时是相同的：

These two pieces of code are identical at the first blush:

class IndexView(generic.ListView):
    template_name = 'polls/index.html'
    context_object_name = 'latest_poll_list'
    queryset = Poll.active.order_by('-pub_date')[:5]

和

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

    def get_queryset(self):
        return Poll.active.order_by('-pub_date')[:5]

它们之间是否有任何区别？如果是这样的话：

Is there any difference between them? And if it is:

哪种方法更好？还是设置 queryset 变量比覆盖 get_queryset 方法更好？

What approach is better? Or when setting queryset variable is better than override the get_queryset method? And vice versa.

推荐答案

在您的示例中，覆盖 queryset 和 get_queryset 具有相同的效果。我会稍微喜欢设置 queryset ，因为它不太冗长。

In your example, overriding queryset and get_queryset have the same effect. I would slightly favour setting queryset because it's less verbose.

当您设置 queryset ，启动服务器时，只会创建一次查询集。另一方面，每个请求都调用 get_queryset 方法。

When you set queryset, the queryset is created only once, when you start your server. On the other hand, the get_queryset method is called for every request.

这意味着 get_queryset 在要动态调整查询时非常有用。例如，您可以返回属于当前用户的对象：

That means that get_queryset is useful if you want to adjust the query dynamically. For example, you could return objects that belong to the current user:

class IndexView(generic.ListView):
    def get_queryset(self):
        """Returns Polls that belong to the current user"""
        return Poll.active.filter(user=self.request.user).order_by('-pub_date')[:5]

另一个示例，其中 get_queryset 很有用，当您想基于可调用项进行过滤时，例如返回今天的民意调查：

Another example where get_queryset is useful is when you want to filter based on a callable, for example, return today's polls:

class IndexView(generic.ListView):
    def get_queryset(self):
        """Returns Polls that were created today"""
        return Poll.active.filter(pub_date=date.today())

如果您尝试通过设置 queryset ，然后 date.today（）只会在加载视图时被调用一次，并且一段时间后视图将显示错误的结果。

If you tried to do the same thing by setting queryset, then date.today() would only be called once, when the view was loaded, and the view would display incorrect results after a while.

class IndexView(generic.ListView):
    # don't do this!
    queryset = Poll.active.filter(pub_date=date.today())

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