old_contents: from django.db import models
  from django.conf import settings
  
  
  class Tag(models.Model):
  
      name = models.TextField(
              max_length=10,
              )
  
      update_at = models.DateTimeField(
              auto_now_add=True,
              )
  
      create_at = models.DateTimeField(
              auto_now=True,
              )
  
      def __str__(self):
          return "#{tag}".format(
                  tag=self.name
                  )
  
new_contents: from django.db import models
  from django.conf import settings
  
  
  class Tag(models.Model):
  
      name = models.TextField(
              max_length=10,
              unique=True,
              )
  
      update_at = models.DateTimeField(
              auto_now_add=True,
              )
  
      create_at = models.DateTimeField(
              auto_now=True,
              )
  
      def __str__(self):
          return "#{tag}".format(
                  tag=self.name
                  )
  
subject: add unique config