Selected Related Example with Querysets

models.py

from django.db import models
from localflavor.us.models import USStateField


class State(models.Model):
    name = USStateField(unique=True)
    incits_code = models.CharField(max_length=250)
    
    class Meta:
        ordering = ['name', ]


class County(models.Model):
    name = models.CharField(max_length=250)
    state = models.ForeignKey(State)
    objects = CountyManager()

    class Meta:
        verbose_name_plural = 'Counties'
        unique_together = ('name', 'state')
        ordering = ['name', ]
    
    def __unicode__(self):
        return self.county_and_state_display
    
    @property
    def county_and_state_display(self):
        """
        Returns a human-readable display of counties and states
        """
        return u'{0}, {1}'.format(self.name, self.state)


class CountyManager(models.Manager):
    def get_queryset(self):
        return super(CountyManager, self).get_queryset().select_related('state')