An example of chained foreign keys using django-smart-selects from PyPi.

models.py

from django.conf import settings
from django.contrib.gis.db import models
from smart_selects.db_fields import ChainedForeignKey 
from common.models import AuditableModel
from ubigeos import strings 


class Department(models.Model):
    """
    A peruvian department.
    """

    name = models.CharField(
        verbose_name=strings.DEPARTMENT_NAME,
        max_length=128,
    )

    def __unicode__(self):
        return self.name

    class Meta:
        verbose_name = strings.DEPARTMENT_VERBOSE_NAME
        verbose_name_plural = strings.DEPARTMENT_VERBOSE_NAME_PLURAL

    @staticmethod
    def get_or_create_from_name(name):
        try:
            return Department.objects.get(name=name)
        except Department.DoesNotExist:
            obj = Department(name=name)
            obj.save()
            return obj
        

class Province(models.Model):
    """
    A peruvian province.
    """

    name = models.CharField(
        verbose_name=strings.PROVINCE_NAME,
        max_length=128,
    )

    department = models.ForeignKey(Department,
        verbose_name=strings.PROVINCE_DEPARTMENT
    )

    def __unicode__(self):
        return self.name

    class Meta:
        verbose_name = strings.PROVINCE_VERBOSE_NAME
        verbose_name_plural = strings.PROVINCE_VERBOSE_NAME_PLURAL

    @staticmethod
    def get_or_create_from_csv_record(record, delimiter=','):
        parts = record.split(delimiter)
        department_name = parts[0].strip()
        province_name = parts[1].strip()
        # Get or create deparment
        department = Department.get_or_create_from_name(department_name)
        # Get or create province
        try:
            return Province.objects.get(
                name=province_name, 
                department=department
            )
        except Province.DoesNotExist:
            obj = Province(name=province_name, department=department)
            obj.save()
            return obj


class District(models.Model):
    """
    A peruvian district.
    """

    name = models.CharField(
        verbose_name=strings.DISTRICT_NAME,
        max_length=128,
    )

    province = models.ForeignKey(Province,
        verbose_name=strings.DISTRICT_PROVINCE
    )

    def __unicode__(self):
        return self.name

    class Meta:
        verbose_name = strings.DISTRICT_VERBOSE_NAME
        verbose_name_plural = strings.DISTRICT_VERBOSE_NAME_PLURAL

    @staticmethod
    def get_or_create_from_csv_record(record, delimiter=','):
        parts = record.split(delimiter)
        department_name = parts[0]
        province_name = parts[1]
        district_name = parts[2]
        # Get or create province
        province = Province.get_or_create_from_csv_record(
            record=("%s%s%s" % (department_name, delimiter, province_name,)),
            delimiter=delimiter
        )
        # Get or create district
        try:
            return District.objects.get(
                name=district_name, 
                province=province
            )
        except District.DoesNotExist:
            obj = District(
                name=district_name,
                province=province
            )
            obj.save()
            return obj


class Ubigeo(models.Model):
    """
    A peruvian ubigeo code.
    """

    code = models.CharField(
        verbose_name=strings.UBIGEO_CODE,
        max_length=6,
        unique=True
    )

    department = models.ForeignKey(Department,
        verbose_name=strings.UBIGEO_DEPARTMENT,
        blank=True,
        null=True
    )

    province = ChainedForeignKey(Province,
        verbose_name=strings.UBIGEO_PROVINCE,
        chained_field="department",
        chained_model_field="department", 
        show_all=False, 
        auto_choose=True,
        blank=True,
        null=True
    )

    district = ChainedForeignKey(District,
        verbose_name=strings.UBIGEO_DISTRICT,
        chained_field="province",
        chained_model_field="province", 
        show_all=False, 
        auto_choose=True,
        blank=True,
        null=True
    )

    def __unicode__(self):
        return self.code

    class Meta:
        verbose_name = strings.UBIGEO_VERBOSE_NAME
        verbose_name_plural = strings.UBIGEO_VERBOSE_NAME_PLURAL

hello dear Sir,
i want your help regarding all the things that has to be done for using ChainedForeignKey
i've been trying for so many days..