old_contents: from django.db import models
  from model_utils.models import TimeStampedModel
  
  from warp.users.models import User
  
  
  class Presentation(TimeStampedModel):
      subject = models.CharField(max_length=50)
      author = models.ForeignKey(User, on_delete=models.CASCADE)
      views = models.IntegerField(default=0)
      is_public = models.BooleanField(default=True)
  
  
  class Slide(TimeStampedModel):
      presentation = models.ForeignKey(Presentation, on_delete=models.CASCADE)
      slide_order = models.PositiveSmallIntegerField()
      markdown = models.TextField()
      html = models.TextField()
  
new_contents: from django.db import models
  from model_utils.models import TimeStampedModel
  
  from warp.users.models import User
  
  
  class Presentation(TimeStampedModel):
      subject = models.CharField(max_length=50)
      author = models.ForeignKey(User, on_delete=models.CASCADE)
      views = models.IntegerField(default=0)
      is_public = models.BooleanField(default=True)
  
      def __str__(self):
          return self.subject
  
  
  class Slide(TimeStampedModel):
      presentation = models.ForeignKey(Presentation, on_delete=models.CASCADE)
      slide_order = models.PositiveSmallIntegerField()
      markdown = models.TextField()
  
      def __str__(self):
          return self.markdown
  
subject: Add __str__ on models