如何在创建模型实例时创建特殊函数？

from django.db import models
from django.utils import timezone

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    pub_date = models.DateTimeField('date published', auto_now_add=True)

    def save(self, *args, **kwargs):
        if not self.id:  # 只有在创建新实例时才设置pub_date
            self.pub_date = timezone.now()
        super(Post, self).save(*args, **kwargs)

    @classmethod
    def create_post(cls, title, content):
        post = cls(title=title, content=content)
        post.save()
        return post

def set_pub_date(func):
    def wrapper(self, *args, **kwargs):
        if not self.id:
            self.pub_date = timezone.now()
        return func(self, *args, **kwargs)
    return wrapper

class Post(models.Model):
    # ... 其他字段 ...

    @set_pub_date
    def save(self, *args, **kwargs):
        super(Post, self).save(*args, **kwargs)