django - 嵌套查询过滤器_Django

Question

我保持简单。我有 3 个模型。

 class C(models.model):
    some_field = models.BooleanField(default=False)

 class B(models.model):
    b = models.ForeignKey(C)

 class A(models.model):
    a = models.ForeignKey(B)

我需要一个获取 A.a.b.some_field = True 的查询过滤器。我怎样才能做到这一点？

Answer 1

您可以过滤满足此条件的 A 对象:

A.objects.filter(<b>a__b__some_field=True</b>)

这将生成一个看起来或多或少像这样的查询:

SELECT a.*
FROM a
JOIN b ON a.a_id = b.id
JOIN c ON b.b_id = c.id
WHERE c.some_field = 1

双下划线 (__) 可用于“透视”关系(如 ForeignKey、OneToOneField 和 ManyToManyField)。如果它是...对多字段，这是存在量化的。但这里的 ForeignKey 是多对一关系，所以这无关紧要。

Note: ForeignKeys to B (or C) is typically named b (or c), not a (or b), since that is the name of the current model. The name of a relation typically specifies how the object(s) it targets relate to the current model.