Django模型API通过中间表反向查找多对多关系

问题描述

我有一个居民，但似乎无法获取该居民所属的SSA集合。我试过res.ssa_set.all().ssas_set.all()和.ssa_resident_set.all()。似乎做不到。通过另一个表进行反向M2M查找的语法是什么？

编辑：我收到‘QuerySet as no Attribute’错误。ERM？

class SSA(models.Model):
    name = models.CharField(max_length=100)
    cost_center = models.IntegerField(max_length=4)
    street_num = models.CharField(max_length=9)
    street_name = models.CharField(max_length=40)
    suburb = models.CharField(max_length=40)
    post_code = models.IntegerField(max_length=4, blank=True, null=True)

    def __unicode__(self):
        return self.name

class Resident(models.Model):
    cris_id = models.CharField(max_length=10, primary_key=True)
    first_name = models.CharField(max_length=20)
    last_name = models.CharField(max_length=20)
    ssas = models.ManyToManyField('SSA', through='SSA_Resident', verbose_name="SSAs")

    def __unicode__(self):
        return self._get_full_name()

    def _get_full_name(self):
        return u"%s %s" %(self.first_name, self.last_name)

    full_name = property(_get_full_name)

class SSA_Resident(models.Model):
    id = models.AutoField(primary_key=True)
    resident = models.ForeignKey('Resident')
    ssa = models.ForeignKey('SSA', verbose_name="SSA")
    active = models.BooleanField(default=True)
    def __unicode__(self):
        return u"%s - %s" %(self.resident.full_name, self.ssa.name)

推荐答案

我正在尝试计算查询集对象，而不是对象本身。对查询集执行GET，然后查找关系集就可以很好地工作。我要换成社区维基，把这个留在这里，以防其他人像我一样愚蠢。

工作示例：

resident = Resident.objects.filter(name='Johnny')
resident.ssa_set.all() # fail
resident = resident.get() # will fail if more than one returned by filter
resident.ssa_set.all() # works, since we're operating on an instance, not a queryset