text: from djmodels.contrib.contenttypes.fields import (
      GenericForeignKey, GenericRelation,
  )
  from djmodels.contrib.contenttypes.models import ContentType
  from djmodels.db import models
  
  
  class Square(models.Model):
      root = models.IntegerField()
      square = models.PositiveIntegerField()
  
      def __str__(self):
          return "%s ** 2 == %s" % (self.root, self.square)
  
  
  class Person(models.Model):
      first_name = models.CharField(max_length=20)
      last_name = models.CharField(max_length=20)
  
      def __str__(self):
          return '%s %s' % (self.first_name, self.last_name)
  
  
  class SchoolClass(models.Model):
      year = models.PositiveIntegerField()
      day = models.CharField(max_length=9, blank=True)
      last_updated = models.DateTimeField()
  
  
  class VeryLongModelNameZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ(models.Model):
      primary_key_is_quite_long_zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz = models.AutoField(primary_key=True)
      charfield_is_quite_long_zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz = models.CharField(max_length=100)
      m2m_also_quite_long_zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz = models.ManyToManyField(Person, blank=True)
  
  
  class Tag(models.Model):
      name = models.CharField(max_length=30)
      content_type = models.ForeignKey(ContentType, models.CASCADE, related_name='backend_tags')
      object_id = models.PositiveIntegerField()
      content_object = GenericForeignKey('content_type', 'object_id')
  
  
  class Post(models.Model):
      name = models.CharField(max_length=30)
      text = models.TextField()
      tags = GenericRelation('Tag')
  
      class Meta:
          db_table = 'CaseSensitive_Post'
  
  
  class Reporter(models.Model):
      first_name = models.CharField(max_length=30)
      last_name = models.CharField(max_length=30)
  
      def __str__(self):
          return "%s %s" % (self.first_name, self.last_name)
  
  
  class ReporterProxy(Reporter):
      class Meta:
          proxy = True
  
  
  class Article(models.Model):
      headline = models.CharField(max_length=100)
      pub_date = models.DateField()
      reporter = models.ForeignKey(Reporter, models.CASCADE)
      reporter_proxy = models.ForeignKey(
          ReporterProxy,
          models.SET_NULL,
          null=True,
          related_name='reporter_proxy',
      )
  
      def __str__(self):
          return self.headline
  
  
  class Item(models.Model):
      name = models.CharField(max_length=30)
      date = models.DateField()
      time = models.TimeField()
      last_modified = models.DateTimeField()
  
      def __str__(self):
          return self.name
  
  
  class Object(models.Model):
      related_objects = models.ManyToManyField("self", db_constraint=False, symmetrical=False)
  
      def __str__(self):
          return str(self.id)
  
  
  class ObjectReference(models.Model):
      obj = models.ForeignKey(Object, models.CASCADE, db_constraint=False)
  
      def __str__(self):
          return str(self.obj_id)
  
  
  class RawData(models.Model):
      raw_data = models.BinaryField()
  
  
  class Author(models.Model):
      name = models.CharField(max_length=255, unique=True)
  
  
  class Book(models.Model):
      author = models.ForeignKey(Author, models.CASCADE, to_field='name')
  