old_contents: from django.db import models
  import swapper
  
  
  class BaseType(models.Model):
      name = models.CharField(max_length=255)
  
      class Meta:
          abstract = True
  
  
  class Type(BaseType):
      class Meta:
          swappable = swapper.swappable_setting("default_app", "Type")
  
  
  class Item(models.Model):
      type = models.ForeignKey(swapper.get_model_name('default_app', "Type"))
      name = models.CharField(max_length=255)
      description = models.TextField()
  
new_contents: from django.db import models
  import swapper
  
  
  class BaseType(models.Model):
      name = models.CharField(max_length=255)
  
      class Meta:
          abstract = True
  
  
  class Type(BaseType):
      class Meta:
          swappable = swapper.swappable_setting("default_app", "Type")
  
  
  class Item(models.Model):
      type = models.ForeignKey(
          swapper.get_model_name('default_app', "Type"), on_delete=models.CASCADE
      )
      name = models.CharField(max_length=255)
      description = models.TextField()
  
subject: Add on_delete to ForeignKey