问题描述
这两段代码乍一看是一样的:
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]
它们之间有什么区别吗?如果是:
Is there any difference between them? And if it is:
哪种方法更好?或者当设置 queryset
变量比覆盖 get_queryset
方法更好?反之亦然.
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.我稍微倾向于设置 queryset
因为它不那么冗长.
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
时,查询集只会在您启动服务器时创建一次.另一方面,每个请求都会调用 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.
这意味着如果您想动态调整查询,get_queryset
很有用.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 get_queryset
有用的例子是当你想根据一个可调用对象进行过滤时,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())
如果你试图通过设置 queryset
来做同样的事情,那么 date.today()
只会在视图加载时被调用一次,并且视图一段时间后会显示不正确的结果.
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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