old_contents: import datetime
  
  from django.db import models
  from django.core.validators import RegexValidator
  
  
  class Link(models.Model):
      url = models.URLField(max_length=2083)
      alias = models.CharField(max_length=255, unique=True, validators=[
          RegexValidator(
              regex=r'^[a-z0-9-_]+$',
              code='invalid_alias',
              message='Alias can only contain lowercase alphabets, numerals, underscores and hyphens',
          ),
      ])
      clicks_count = models.PositiveIntegerField(default=0)
      date_created = models.DateField(auto_now_add=True)
  
      def __str__(self):
          return '{0} -> {1}'.format(self.alias, self.url)
  
new_contents: from django.db import models
  from django.core.validators import RegexValidator
  
  
  class Link(models.Model):
      url = models.URLField(max_length=2083)
      alias = models.CharField(max_length=255, unique=True, validators=[
          RegexValidator(
              regex=r'^[a-z0-9-_]+$',
              code='invalid_alias',
              message='Alias can only contain lowercase alphabets, numerals, underscores and hyphens',
          ),
      ])
      clicks_count = models.PositiveIntegerField(default=0)
      date_created = models.DateField(auto_now_add=True)
  
      def __str__(self):
          return '{0} -> {1}'.format(self.alias, self.url)
  
subject: remove unused import