old_contents: from django.db import models
  
  # Create your models here.
  
  class Person(models.Model):
      name = models.CharField(max_length=255)
      birth_date = models.DateTimeField()
      parent = models.ForeignKey('self')
  
  class Family(models.Model):
      members = models.ManyToManyField(Person)
  
new_contents: from datetime import datetime
  
  from django.db import models
  
  # Create your models here.
  
  class Person(models.Model):
      name = models.CharField(max_length=255)
      birth_date = models.DateTimeField(default=datetime.now)
      parent = models.ForeignKey('self', null=True)
  
  class Family(models.Model):
      members = models.ManyToManyField(Person)
  
subject: Tweak models.