class Airline(models.Model):

    code = models.CharField(max_length=3, db_index=True, unique=True)
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return u"%s (%s)" % (self.name, self.code)


class Airport(models.Model):

    code = models.CharField(max_length=4, db_index=True, unique=True)
    name = models.CharField(max_length=100)
    airlines = models.ManyToManyField(Airline)

    def __unicode__(self):
        return u"%s" % self.name