Django外键查询和反向查询

class A(models.Model):
    name= models.CharField('类A', max_length=32)

class B(models.Model):
    a= models.ForeignKey(A, verbose_name='A类',related_name = "test")
    name = models.CharField('类B', max_length=16)

class C(models.Model):
    a= models.ForeignKey(A, verbose_name='A类')
    name = models.CharField('类C', max_length=16)

aa = A.objects.get(id=A_id)

b = B.objects.filter(a=aa).all()