用相关查询集的集合注释

Question

我在解决django ORM查询时遇到麻烦。我有以下型号：

class Container(models.Model):
    name = models.CharField(...)


class ContainerItem(models.Model):
    amount = models.PositiveSmallIntegerField(...)
    date = models.DateTimeField(...)
    container = models.ForeignKey(Container)


class Group(models.Model):
    container = models.ForeignKey(Container)
    start_datetime = models.DateTimeField(...)
    end_datetime = models.DateTimeField(...)

对于Group查询集，我需要用amount ContainerItems内的group的{​​{1}}字段的总和来注释组。和start_datetime。到目前为止，这就是我所得到的，但是我不断得到end_datetime

'This queryset contains a reference to an outer query and may only be used in a subquery.'