text: from django.db import models
  from django.contrib.auth.models import User
  
  
  class PrivateMessage(models.Model):
      id = models.AutoField(primary_key=True)
      title = models.CharField(max_length=127)
      text = models.TextField()
      sent_date = models.DateField(auto_now_add=True, null=True)
      to_address = models.CharField(max_length=255)
      from_address = models.CharField(max_length=255)
      
      def __str__(self):
          return "From: " + self.from_address + " To: " + self.to_address + " Title: " + self.title
      
      class Meta:
          db_table = 'at_private_messages'
  
  
  class Teacher(models.Model):
      teacher_id = models.AutoField(primary_key=True)
      user = models.ForeignKey(User)
      
      def __str__(self):
          return self.user.first_name + " " + \
              self.user.last_name + " "
      
      class Meta:
          db_table = 'at_teachers'
          
  class Student(models.Model):
      student_id = models.AutoField(primary_key=True)
      user = models.ForeignKey(User)
      
      def __str__(self):
          return self.user.first_name + " " + \
                            self.user.last_name 
      
      class Meta:
          db_table = 'at_students'