Django怎么在一个表中写一个一对多的外键包含另一个包含外键的表

我的需求是这样的，在一个表OneCategory中用models.ManyToManyField('Post')

class Post(models.Model):
    ....
    tag = models.ManyToManyField('Tag')

class OneCategory(models.Model):
    name = models.CharField('一级分类')

我就是想实现这样的功能。

模型大意：表A中有外键链接到表B，表B中包含其他的外键，表C、D、E 等不包含外键。

我写了这样的模型，老是出现错误，有什么要注意的，我是新手大家看看我的代码错在哪里。

我的 models.py 代码

from django.db import models

class Post(models.Model):
    title = models.CharField('标题', max_length=100)
    content = models.TextField('内容')
    tag = models.ManyToManyField('Tag',blank=True)
    category = models.ForeignKey('Category',blank=True)
    comment = models.ManyToManyField('Comment',blank=True)
    pub_date = models.DateTimeField('发布日期', auto_now_add=True)

    def __str__(self):
        return self.title

    class Meta:
        verbose_name = '文章'
        verbose_name_plural = '文章'

class Category(models.Model):
    name = models.CharField('名称', max_length=30)
    des = models.CharField('描述', max_length=300)
    pub_date = models.DateTimeField('创建日期', auto_now_add=True, null=True)

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = '分类'
        verbose_name_plural = '分类'

class Tag(models.Model):
    name = models.CharField('名称', max_length=20)
    pub_date = models.DateTimeField('创建日期', auto_now_add=True, null=True)

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = '标签'
        verbose_name_plural = '标签'

class OneCategory(models.Model):
    name = models.CharField('一级分类', max_length=25)
    des = models.CharField('描述', max_length=300)
    pub_date = models.DateTimeField('创建日期', auto_now_add=True, null=True)
   post = models.ManyToManyField('Post',blank=True)

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = '主分类'
        verbose_name_plural = '主分类'

class Comment(models.Model):
    nickname = models.CharField('昵称'


    
, max_length=20)
    email = models.EmailField('邮箱', max_length=50)
    website = models.URLField('站点', blank=True)
    content = models.TextField('内容', max_length=1500)
    pub_date = models.DateTimeField('发布日期', auto_now_add=True, null=True)

    def __str__(self):
        return self.nickname

    class Meta:
        verbose_name = '评论'
        verbose_name_plural= '评论'

class Employeeship(models.Model): user = models.ForeignKey( User, on_delete=models.PROTECT, null = True, ) department = models.ForeignKey( Department, on_delete=models.PROTECT, null = True, ) def __str__ (self): return self.name class Meta: db_table = u'employeeship'

class Department(Common, Rowtracking, Recurrence): company = models.ForeignKey( Company, on_delete=models.PROTECT, null = True, ) #Link department to user employees = models.ManyToManyField( User, through='Employeeship', through_fields=('department', 'user'), ) def __str__ (self): return self.name class Meta: db_table = u'department'