django/tests/modeltests/m2m_signals/models.py

from django.db import models
from django.utils.encoding import python_2_unicode_compatible


@python_2_unicode_compatible
class Part(models.Model):
    name = models.CharField(max_length=20)

    class Meta:
        ordering = ('name',)

    def __str__(self):
        return self.name

@python_2_unicode_compatible
class Car(models.Model):
    name = models.CharField(max_length=20)
    default_parts = models.ManyToManyField(Part)
    optional_parts = models.ManyToManyField(Part, related_name='cars_optional')

    class Meta:
        ordering = ('name',)

    def __str__(self):
        return self.name

class SportsCar(Car):
    price = models.IntegerField()

@python_2_unicode_compatible
class Person(models.Model):
    name = models.CharField(max_length=20)
    fans = models.ManyToManyField('self', related_name='idols', symmetrical=False)
    friends = models.ManyToManyField('self')

    class Meta:
        ordering = ('name',)

    def __str__(self):
        return self.name