old_contents: from django.db import models
  
  class User(models.Model):
      name = models.CharField(max_length=50)
      username = models.CharField(max_length=50, primary_key=True)
      avatar_url = models.CharField(max_length=100)
      def __str__(self):
          return self.name
  
  class Tutorial(models.Model):
      title = models.CharField(max_length=100)
      description = models.CharField(max_length=500)
      repo_url = models.CharField(max_length=100)
      owner = models.ForeignKey(User)
      def __str__(self):
          return self.title
  
  class Step(models.Model):
      title = models.CharField(max_length=100)
      content_before = models.CharField(max_length=500)
      content_after = models.CharField(max_length=500)
      tutorial = models.ForeignKey(Tutorial)
      def __str__(self):
          return self.title
  
  class Commit(models.Model):
      commit_url = models.CharField(max_length=100)
      code_url = models.CharField(max_length=100)
      step = models.OneToOneField(Step)
      def __str__(self):
          return commit_url
  
  class File(models.Model):
      commit = models.ForeignKey(Commit)
      name = models.CharField(max_length=100)
      def __str__(self):
          return name
  
  class Line(models.Model):
      src_file = models.ForeignKey(File)
      number = models.IntegerField()
      content = models.CharField(max_length=200)
      addition = models.BooleanField()
      deletion = models.BooleanField()
      def __str__(self):
          return content
  
new_contents: from django.db import models
  
  class User(models.Model):
      name = models.CharField(max_length=50)
      username = models.CharField(max_length=50, primary_key=True)
      avatar_url = models.CharField(max_length=100)
      def __str__(self):
          return self.name
  
  class Tutorial(models.Model):
      title = models.CharField(max_length=100)
      description = models.CharField(max_length=500)
      repo_url = models.CharField(max_length=100)
      owner = models.ForeignKey(User)
      def __str__(self):
          return self.title
  
  class Step(models.Model):
      title = models.CharField(max_length=100)
      content_before = models.CharField(max_length=500)
      content_after = models.CharField(max_length=500)
      tutorial = models.ForeignKey(Tutorial)
      def __str__(self):
          return self.title
  
  class Commit(models.Model):
      commit_url = models.CharField(max_length=100)
      code_url = models.CharField(max_length=100)
      step = models.OneToOneField(Step)
      def __str__(self):
          return commit_url
  
  class File(models.Model):
      commit = models.ForeignKey(Commit)
      name = models.CharField(max_length=100)
      def __str__(self):
          return name
  
  class Line(models.Model):
      src_file = models.ForeignKey(File)
      number = models.IntegerField()
      content = models.CharField(max_length=200)
      addition = models.BooleanField(default=False)
      deletion = models.BooleanField(default=False)
      def __str__(self):
          return content
  
subject: Set default values for bools in models