python - 排除 vs 过滤器，当使用 Q 对象时

Question

无法理解这是怎么可能的:

A = object_list.filter( Q(sales__sale_starts__lte=today) & Q(sales__sale_ends__gte=today) )
# query inside filter catches 2 objects

B = object_list.exclude( Q(sales__sale_starts__lte=today) & Q(sales__sale_ends__gte=today) )
# query inside exclude catches 3 objects,
# though it is the same as previous

# in other words: object_list contains 20 objects,
# A - 2 objects, and B - 17 objects

使用 Q 对象时，filter() 和 exclude() 的工作方式有什么不同吗？谢谢。

我希望 B 如下所示:

B = object_list.difference(A)
# B contains 18 objects

Answer 1

行为应该是一样的。如果您查看 .exclude() 和 .filter() 源代码，它们的作用相同:

def exclude(self, *args, **kwargs):
    """
    Returns a new QuerySet instance with NOT (args) ANDed to the existing
    set.
    """
    return self._filter_or_exclude(True, *args, **kwargs)

def filter(self, *args, **kwargs):
    """
    Returns a new QuerySet instance with the args ANDed to the existing
    set.
    """
    return self._filter_or_exclude(False, *args, **kwargs)

而 _filter_or_exclude() 只是用 ~ 否定你的 Q 过滤器

def _filter_or_exclude(self, negate, *args, **kwargs):
    if args or kwargs:
        assert self.query.can_filter(), \
            "Cannot filter a query once a slice has been taken."

    clone = self._clone()
    if negate:
        clone.query.add_q(~Q(*args, **kwargs))
    else:
        clone.query.add_q(Q(*args, **kwargs))
    return clone