old_contents: from django.db import models
  
  class Task(models.Model):
      owner = models.ForeignKey('TaskOwner', on_delete=models.CASCADE)
      source = models.TextField()
      dest = models.TextField()
      content = models.TextField()
      ready_time = models.DateTimeField(auto_now=True, auto_now_add=True)
      modified = models.DateTimeField(auto_now=True, auto_now_add=True)
  
  class TaskOwner(models.Model):
      email = models.EmailField()
      key = models.CharField(max_length=255)
      modified = models.DateTimeField(auto_now=True, auto_now_add=True)
  
new_contents: from django.db import models
  
  class Task(models.Model):
      owner = models.ForeignKey('TaskOwner', on_delete=models.CASCADE)
      source = models.CharField(max_length=255)
      dest = models.CharField(max_length=255)
      content = models.TextField()
      ready_time = models.DateTimeField(auto_now=True, auto_now_add=True)
      modified = models.DateTimeField(auto_now=True, auto_now_add=True)
  
  class TaskOwner(models.Model):
      email = models.EmailField()
      key = models.CharField(max_length=255)
      modified = models.DateTimeField(auto_now=True, auto_now_add=True)
  
subject: change fields to indexable type for equality queries for duplicates