Dfyjkt

This is my model (the relevant part):

class Country(models.Model):
 name = models.CharField(max_length=500, choices=COUNTRY_NAME_CHOICE)
 country_id = models.CharField(max_length=500,choices=COUNTRY_ID_CHOICE,primary_key=True,unique=True)
 def __str__(self):
 return self.name

class City(models.Model):
 name = models.CharField(max_length=500,choices=CITY_NAME_CHOICE)
 country = models.ForeignKey('Country',on_delete=models.CASCADE)
 zip= models.CharField(max_length=500, choices=ZIP_CHOICE, primary_key=True,unique=True)
 def __str__(self):
 return self.name

class Cost(models.Model):
 date = models.ForeignKey('Date' ,on_delete=models.CASCADE)
 city= models.ForeignKey('City' ,on_delete=models.CASCADE)
 value = models.FloatField(validators=[MinValueValidator(0)])
 entry_time = models.DateTimeField(auto_now_add=True)
 user = models.ForeignKey(User, on_delete=models.CASCADE)
 def __str__(self):
 return self.city.name + ' ' +str(self.value) 

For model Cost, I have a Django form CostForm that I am listing out on a template, so that users can insert new costs.

class CostForm(ModelForm):
 class Meta:
 model = Cost
 exclude = ['user','entry_time'] 

 #Makes only FR, NO, and RU cities available 
 def __init__(self, *args, **kwargs):
 super(CostForm, self).__init__(*args, **kwargs)
 self.fields['city'].queryset = City.objects.filter(country__name__in=['France','Norway','Russia'])

On the template city field is shown as a dropdown. I have already managed to limit this field to the values I want in the form above (user can input costs only for Russia, Norway and France, because their cities are the only options they see in the dropdown).

Here is my problem: I need to make another option available for the
users in the city dropdown. A city that doesn't exist for real in the
database. Lets call it "X". When user chooses city X, that would be a
sign that I need to do some additional calculations in the backend, and
split up cost between some other cities.

I thought I could manually add this city X to the queryset in the CostForm, but after some extensive research I hit the wall. Everyone is saying that the queryset object is not there to be edited, but only represents the result of a query.

Then I tried editing the dropdown in javascript and adding a new option for city X there, and I managed, BUT, I cannot work with this entry with city X, because the form is not valid. So, the user just gets the message similar to "Please choose a valid option for the field".

So now I am back to exploring the possibility of adding this city X manually to the queryset in the CostForm... Does anyone know how?? Also, if you have any other ideas on how I could solve this problem, please share.