django REST api通用视图的queryset属性 [英] the queryset attribute of django REST api generic views

问题描述

我试图理解django rest框架的通用API视图，该文档告诉我，虽然覆盖了通用视图的方法，但我不应该访问 queryset 属性直接访问，而是访问 get_queryset（）函数，因为显然queryset属性仅被评估一次， get_queryset（）做不同的事吗？
queryset属性是否曾经更新过？

I am trying to understand the django rest framework generic API views, the documentation tells me that while overriding methods of the generic views, I shouldn't be accessing the queryset attribute directly and instead access the get_queryset() function because apparently the queryset attribute is evaluated only once, what does the get_queryset() do differently? Does the queryset attribute ever get updated?

推荐答案

要进一步扩展，请源代码会告诉你真相。

To further expand, the source code will tell you the truth.

    assert self.queryset is not None, (
        "'%s' should either include a `queryset` attribute, "
        "or override the `get_queryset()` method."
        % self.__class__.__name__
    )

    queryset = self.queryset
    if isinstance(queryset, QuerySet):
        # Ensure queryset is re-evaluated on each request.
        queryset = queryset.all()
    return queryset

• 首先检查查询集是否已定义


• 其次检查指定的查询集是否为Django Queryset类的实例


• 再次对其进行重新评估（进行数据库查询）查询集并设置结果


• 第四次返回结果


• First it checks queryset is defined
• Second it checks if the queryset specified is an instance of Django's Queryset class
• Third it re-evaluates (makes a database query) the queryset and sets the results
• Fourth it returns the results

有关直接使用self.queryset的警告是，对结果进行评估时会缓存结果，因此与使用self.get_queryset（）相对，对该值的进一步引用将是最新的。

The warning about using self.queryset directly is that results are cached when evaluated so further references to this value will not be up to date as opposed of using self.get_queryset().

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