如何解决Django查询“'ExtractHour'对象没有'split'属性”错误？

Question

我使用的是Django和python3.7。我想在较大查询的条件中包含子查询。

from django.db.models.functions import ExtractHour
...
hour_filter = ExtractHour(ExpressionWrapper(
            F("article__created_on") + timedelta(0, avg_fp_time_in_seconds),
            output_field=models.DateTimeField()
        ),
)
query = StatByHour.objects.filter(hour_of_day=OuterRef(hour_filter))

...

包含它的更大的查询是

^{pr2}$

但是，当我运行这个时，我得到了错误

'ExtractHour' object has no attribute 'split'

这意味着什么？我如何调整我的过滤器，使这个错误消失？

编辑：添加生成外部查询的对象的模型。。。

class ArticleStat(models.Model):
    objects = ArticleStatManager()
    article = models.ForeignKey(Article, on_delete=models.CASCADE, related_name='articlestats')
    ...
    votes = models.FloatField(default=0, null=False)

Answer 1

OuterRef用于从父查询获取一个值，但是这里您根本不需要外部查询的引用。在

from django.db.models.functions import ExtractHour

hour_filter = ExtractHour(
    ExpressionWrapper(
        F('article__created_on') + timedelta(0, avg_fp_time_in_seconds),
        output_field=models.DateTimeField()
    )
)
query = StatByHour.objects.filter(hour_of_day=hour_filter)

所以这里不需要OuterRef。正如documentation on ^{}所说：

Use OuterRef when a queryset in a Subquery needs to refer to a field from the outer query. It acts like an F expression except that the check to see if it refers to a valid field isn’t made until the outer queryset is resolved.