I have three model classes that look as below:

class Model(models.Model):
   model = models.CharField(max_length=20, blank=False)
   manufacturer = models.ForeignKey(Manufacturer)
   date_added = models.DateField(default=datetime.today)
   def __unicode__(self):
      name = ''+str(self.manufacturer)+" "+str(self.model)
      return name 

class Series(models.Model):
   series = models.CharField(max_length=20, blank=True, null=True)
   model = models.ForeignKey(Model)
   date_added = models.DateField(default=datetime.today)
   def __unicode__(self):
      name = str(self.model)+" "+str(self.series)
      return name
class Manufacturer(models.Model):
   MANUFACTURER_POPULARITY_CHOICES = (
      ('1', 'Primary'),
      ('2', 'Secondary'),
      ('3', 'Tertiary'),
   )

   manufacturer = models.CharField(max_length=15, blank=False)
   date_added = models.DateField(default=datetime.today)
   manufacturer_popularity = models.CharField(max_length=1,
      choices=MANUFACTURER_POPULARITY_CHOICES)
   def __unicode__(self):
      return self.manufacturer

I want to have the fields for model series and manufacturer represented as dropdowns instead of text fields. I have customized the model forms as below:

class SeriesForm(ModelForm):
   series = forms.ModelChoiceField(queryset=Series.objects.all())
   class Meta:
      model = Series
      exclude = ('model', 'date_added',)

class ModelForm(ModelForm):
   model = forms.ModelChoiceField(queryset=Model.objects.all())
   class Meta:
      model = Model
      exclude = ('manufacturer', 'date_added',)

class ManufacturerForm(ModelForm):
   manufacturer = forms.ModelChoiceField(queryset=Manufacturer.objects.all())
   class Meta:
      model = Manufacturer
      exclude = ('date_added',)

However, the dropdowns are populated with the unicode in the respective class...how can I further customize this to get the end result I want?

Also, how can I populate the forms with the correct data for editing? Currently only SeriesForm is populated. The starting point of all this is from another class whose declaration is as below:

class CommonVehicle(models.Model):
   year = models.ForeignKey(Year)
   series = models.ForeignKey(Series)
   ....

   def __unicode__(self):
      name = ''+str(self.year)+" "+str(self.series)
      return name