old_contents: from .base import BaseModel
  
  
  class Post(BaseModel):
  
      def __init__(self, **kwargs):
          self.kind = "Post"
          super().__init__(self.kind, **kwargs)
  
new_contents: from .base import BaseModel
  
  
  class Post(BaseModel):
  
      def __init__(self, **kwargs):
          self.kind = "Post"
          super().__init__(self.kind, **kwargs)
          self.comment_list = self.data.get("comment_list")
  
      def add_comment(self, comment_id):
          if not self.comment_list:
              self.comment_list = self.data["comment_list"] = []
          self.comment_list.append(comment_id)
          self.update()
  
      def update(self, entity_id=None, data=None):
          if not entity_id and not data:
              return super().update(self.data.get("id"), self.data)
          return super().update(entity_id, data)
  
subject: Update post model, add an add method and extends update