old_contents: from django.db import models
  
  class Profile(models.Model):
      user = models.EmailField(unique=True)
      nickname = models.CharField(max_length=64, blank=True)
      intro = models.TextField(max_length=256, blank=True)
  
  
new_contents: from django.db import models
  from django.core.cache import cache
  from django.dispatch import receiver
  
  from settings import EMAIL_ID_CACHE_PREFIX, EMAIL_ID_CACHE_TIMEOUT
  from registration.signals import user_registered
  
  class Profile(models.Model):
      user = models.EmailField(unique=True)
      nickname = models.CharField(max_length=64, blank=True)
      intro = models.TextField(max_length=256, blank=True)
  
  
  @receiver(user_registered)
  def clean_email_id_cache(sender, **kwargs):
      user = kwargs['user']
      cache.set(EMAIL_ID_CACHE_PREFIX+user.email, user.id, EMAIL_ID_CACHE_TIMEOUT)
  
subject: Update email_id cache when user has registered