text: from __future__ import unicode_literals
  
  from django.contrib.contenttypes.fields import (
      GenericForeignKey, GenericRelation
  )
  from django.contrib.contenttypes.models import ContentType
  from django.db import models, connection
  from django.utils.encoding import python_2_unicode_compatible
  
  
  @python_2_unicode_compatible
  class Square(models.Model):
      root = models.IntegerField()
      square = models.PositiveIntegerField()
  
      def __str__(self):
          return "%s ** 2 == %s" % (self.root, self.square)
  
  
  @python_2_unicode_compatible
  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()
  
  # Unfortunately, the following model breaks MySQL hard.
  # Until #13711 is fixed, this test can't be run under MySQL.
  if connection.features.supports_long_model_names:
      class VeryLongModelNameZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ(models.Model):
          class Meta:
              # We need to use a short actual table name or
              # we hit issue #8548 which we're not testing!
              verbose_name = 'model_with_long_table_name'
          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, 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'
  
  
  @python_2_unicode_compatible
  class Reporter(models.Model):
      first_name = models.CharField(max_length=30)
      last_name = models.CharField(max_length=30)
      raw_data = models.BinaryField()
  
      def __str__(self):
          return "%s %s" % (self.first_name, self.last_name)
  
  
  class ReporterProxy(Reporter):
      class Meta:
          proxy = True
  
  
  @python_2_unicode_compatible
  class Article(models.Model):
      headline = models.CharField(max_length=100)
      pub_date = models.DateField()
      reporter = models.ForeignKey(Reporter)
      reporter_proxy = models.ForeignKey(ReporterProxy, null=True,
                                         related_name='reporter_proxy')
  
      def __str__(self):
          return self.headline
  
  
  @python_2_unicode_compatible
  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
  
  
  @python_2_unicode_compatible
  class Object(models.Model):
      related_objects = models.ManyToManyField("self", db_constraint=False, symmetrical=False)
  
      def __str__(self):
          return str(self.id)
  
  
  @python_2_unicode_compatible
  class ObjectReference(models.Model):
      obj = models.ForeignKey(Object, db_constraint=False)
  
      def __str__(self):
          return str(self.obj_id)
  