机构里面关联了城市的外键，在机构的表里面生成的是city_id

class CourseOrg(models.Model):
    name = models.CharField(max_length=50, verbose_name=u"机构名称")
    desc = models.TextField(verbose_name=u"机构描述")
    tag = models.CharField(default="全国知名", max_length=10, verbose_name=u"机构标签")
    category = models.CharField(default="pxjg", verbose_name=u"机构类别", max_length=20,
                                choices=(("pxjg", "培训机构"), ("gr", "个人"), ("gx", "高校")))
    click_nums = models.IntegerField(default=0, verbose_name=u"点击数")
    fav_nums = models.IntegerField(default=0, verbose_name=u"收藏数")
    image = models.ImageField(upload_to="org/%Y/%m", verbose_name=u"logo", max_length=100, null=True, blank=True)
    address = models.CharField(max_length=150, verbose_name=u"机构地址")
    city = models.ForeignKey(CityDict, on_delete=models.CASCADE, verbose_name=u"所在城市")
    students = models.IntegerField(default=0, verbose_name=u"学习人数")
    course_nums = models.IntegerField(default=0, verbose_name=u"课程数")
    add_time = models.DateTimeField(default=datetime.now)

为什么xadmin里面显示的是城市的名字，如果我想显示城市的其他字段，比如desc，那怎么改写呢

class CityDict(models.Model):
    desc = models.CharField(max_length=200, verbose_name=u"描述")
    name = models.CharField(max_length=20, verbose_name=u"城市")
    add_time = models.DateTimeField(default=datetime.now)

    class Meta:
        verbose_name = u"城市"
        verbose_name_plural = verbose_name

    def __str__(self):
        return self.name