Question

Welcome,

I have some problem with limiting choices related with ForeignKey. Below I’m attaching fragment of my code (models.py):

class Car(models.Model):
    name = models.CharField(max_length=50)
    ....

class Driver(models.Model):
    name = models.CharField(max_length=50)
    car = models.ForeignKey(Car)
    ....

class CarForm(ModelForm):
    class Meta:
        model = Car

class DriverForm(ModelForm):
    def __init__(self, *args, **kwargs):
        super (DriverForm,self).__init__(*args, **kwargs)
        self.fileds['car'].queryset = Car.objects.filter(???_1_???)    
    class Meta:
        model = Driver

Could anybody give me some advices how should be defined ???1??? to restrict available Car objects only to these which aren’t assign to any Driver?

Answer 1

First of all, you may want to consider changing the relationship between Car and Driver to a OneToOneField rather than a ForeignKey if each Car can always only have a single Driver.

However, if you just want to restrict the choices in the form, your queryset needs to be something like:

from django.db.models import Count
self.fields['car'].queryset = Car.objects.annotate(num_drivers=Count('driver')).filter(num_drivers=0)