如何在Django中定义模型之间的多态关系？

from django.db import models
from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType

class TaggedItem(models.Model):
    tag = models.SlugField()
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

    def __str__(self):
        return self.tag

from django.db import models
from django.contrib.contenttypes.fields import GenericRelation

class BlogPost(models.Model):
    title = models.CharField(max_length=255)
    content = models.TextField()
    tags = GenericRelation(TaggedItem)

    def __str__(self):
        return self.title

from django.contrib.contenttypes.models import ContentType
from myapp.models import BlogPost, TaggedItem

post = BlogPost.objects.create(title='My first blog post', content='Hello, world!')
tagged_item = TaggedItem.objects.create(tag='python', content_object=post)