django ORM-带Max的子查询

在尝试将Django ORM与子查询和Max函数(db:PostgreSQL 15)一起使用时,我遇到了一些问题

在以下型号上:

class Task(models.Model):
    declaration = models.ForeignKey(
        Declaration,
        null=True,
        default=None,
        on_delete=models.CASCADE,
        related_name="tasks",
    )
    sequence = models.PositiveIntegerField(blank=True, null=True)
    #
    # other fields

我正在尝试筛选与具有最高序列的声明相关的任务 。 以下是我的尝试:

sequences = Task.objects.filter(declaration=OuterRef("declaration")).exclude(sequence__isnull=True).order_by("sequence").distinct().values("sequence")
max_sequences = sequences.annotate(max_seq=Max("sequence")).values("max_seq")
qs = Task.objects.filter(sequence=Subquery(max_sequences))

然而,迭代qs会抛出以下错误:

ProgrammingError: more than one row returned by a subquery used as an expression

检查SQL,如下所示:

SELECT "task"."id",
       "task"."declaration_id",
       "task"."sequence"
FROM "task"
WHERE "task"."sequence" = (
    SELECT "subquery"."max_seq"
    FROM (SELECT DISTINCT MAX(U0."sequence") AS "max_seq", U0."sequence"
            FROM "task" U0
            WHERE (U0."declaration_id" = ("task"."declaration_id") AND
            NOT (U0."sequence" IS NULL))
    GROUP BY U0."sequence"
    ORDER BY U0."sequence" ASC) subquery)

并且执行返回相同的错误。

正在添加 LIMIT 1 到第一个子查询,在dbshell上解决它:

SELECT "task"."id",
       "task"."declaration_id",
       "task"."sequence"
FROM "task"
WHERE "task"."sequence" = (
    SELECT "subquery"."max_seq"
    FROM (SELECT DISTINCT MAX(U0."sequence") AS "max_seq", U0."sequence"
            FROM "task" U0
            WHERE (U0."declaration_id" = ("task"."declaration_id") AND
            NOT (U0."sequence" IS NULL))
    GROUP BY U0."sequence"
    ORDER BY U0."sequence" ASC LIMIT 1) subquery)`

但我不知道如何使用Django查询集。 有什么帮助吗?

谢谢