“QuerySet”对象没有属性错误，试图获取许多tomany字段的相关数据

i have the following models:

我有以下模型:

class Tag(models.Model):
    tag_name = models.CharField(max_length=250)
    tagcat = models.ForeignKey('TagCat')

class Subject(models.Model):
    user = models.ManyToManyField(User)
    tags = models.ManyToManyField(Tag)

class TagCat(models.Model):
    cat_name = models.CharField(max_length=100)
class