old_contents: from django.db import models
  from django.contrib.auth.models import User
  
  class Procedure(models.Model):
      title = models.CharField(max_length=50)
      author = models.CharField(max_length=50)
      uuid = models.IntegerField(null=True)
      version = models.CharField(max_length=50, null=True)
      owner = models.ForeignKey(User, unique=True)
  
  class Page(models.Model):
      procedure = models.ForeignKey(Procedure)
  
new_contents: from django.db import models
  from django.contrib.auth.models import User
  
  class Procedure(models.Model):
      title = models.CharField(max_length=50)
      author = models.CharField(max_length=50)
      uuid = models.IntegerField(null=True, unique=True)
      version = models.CharField(max_length=50, null=True)
      owner = models.ForeignKey(User, unique=True)
  
  class Page(models.Model):
      procedure = models.ForeignKey(Procedure)
  
subject: Make uuid on procedures unique