Creating a dynamic choice field

Question

I'm having some trouble trying to understand how to create a dynamic choice field in django. I have a model set up something like:

class rider(models.Model):
     user = models.ForeignKey(User)
     waypoint = models.ManyToManyField(Waypoint)

class Waypoint(models.Model):
     lat = models.FloatField()
     lng = models.FloatField()

What I'm trying to do is create a choice Field whos values are the waypoints associated with that rider (which would be the person logged in).

Currently I'm overriding init in my forms like so:

class waypointForm(forms.Form):
     def __init__(self, *args, **kwargs):
          super(joinTripForm, self).__init__(*args, **kwargs)
          self.fields['waypoints'] = forms.ChoiceField(choices=[ (o.id, str(o)) for o in Waypoint.objects.all()])

But all that does is list all the waypoints, they're not associated with any particular rider. Any ideas? Thanks.

Answer 1

you can filter the waypoints by passing the user to the form init

class waypointForm(forms.Form):
    def __init__(self, user, *args, **kwargs):
        super(waypointForm, self).__init__(*args, **kwargs)
        self.fields['waypoints'] = forms.ChoiceField(
            choices=[(o.id, str(o)) for o in Waypoint.objects.filter(user=user)]
        )

from your view while initiating the form pass the user

form = waypointForm(user)

in case of model form

class waypointForm(forms.ModelForm):
    def __init__(self, user, *args, **kwargs):
        super(waypointForm, self).__init__(*args, **kwargs)
        self.fields['waypoints'] = forms.ModelChoiceField(
            queryset=Waypoint.objects.filter(user=user)
        )

    class Meta:
        model = Waypoint

Answer 2

There's built-in solution for your problem: ModelChoiceField.

Generally, it's always worth trying to use ModelForm when you need to create/change database objects. Works in 95% of the cases and it's much cleaner than creating your own implementation.