old_contents: from django.db import models
  from django.conf import settings
  
  
  class UserSetting(models.Model):
      user = models.OneToOneField(
          settings.AUTH_USER_MODEL,
          related_name="settings",
      )
  
  
  class ArbitrarySetting(models.Model):
      setting = models.ForeignKey(UserSetting)
      key = models.CharField(max_length=32)
      value = models.CharField(max_length=128)
  
new_contents: from django.db import models
  from django.conf import settings
  
  
  class UserSetting(models.Model):
      user = models.OneToOneField(
          settings.AUTH_USER_MODEL,
          related_name="settings",
      )
  
      def __str__(self):
          return self.user.username
  
  
  class ArbitrarySetting(models.Model):
      setting = models.ForeignKey(UserSetting)
      key = models.CharField(max_length=32)
      value = models.CharField(max_length=128)
  
      def __str__(self):
          return "'%s': '%s' for user %s" % (
              self.key,
              self.value,
              self.setting.user.username,
          )
          
  
subject: add __str__ to the models