Django无法确定简单的注释函数

Question

我试图在一个queryset类上创建一个注释，它只是添加一个布尔值，这是一些标准查询的结果。在

CustomQueryset(models.QuerySet):
    """ An extension of the traditional queryset to support
        filtering on accepting_offers """

    def annotate_with_accepting_offers(self):
        """ Add a lovely little variable to the SELECT that
            says if the listing is accepting offers.

            A <thing> is accepting offers when its:
                + not cancelled
                + expire date is today or in the future
                + has spaces left
        """
        return self.annotate(accepting_offers=Q(cancelled=False) & Q(expire_date__gte=date.today()) & Q(spaces_left__gt=0))

    def accepting_offers(self):
        """ Annotate with 'accepting_offers' and filter the results that are True """
        return self.annotate_with_accepting_offers().filter(accepting_offers=True)

    def not_accepting_offers(self):
        """ Annotate with 'accepting_offers' and filter the results that are False """
        return self.annotate_with_accepting_offers().filter(accepting_offers=False)

可惜这不管用，有什么想法注释会怎样？在

如果这是SQL，那么最上面一行应该是：

^{pr2}$

---

编辑： 我打算创建这个注释的原因是为了使对变量的过滤更容易，这可以在接下来的两个函数中看到。在

这两种方法将在更大的查询链中使用，因此（具有讽刺意味的是）通过注释保持简单应该会有所帮助。在

Answer 1

正如我在评论中提到的，这根本不是Q表达式的用途。我想你想要的是conditional expression：

return self.annotate(
  accepting_offers=Case(
    When(cancelled=False, expire_date__gte=date.today(), spaces_left__gt=0, then=Value(True)),
    default_value=Value(False),
    output_field=models.BooleanField()
  )
)