how to modify choices on admin pages - django

Question

I have a model that has a field named "state":

class Foo(models.Model):
    ...
    state = models.IntegerField(choices = STATES)
    ...

For every state, possible choices are a certain subset of all STATES. For example:

if foo.state == STATES.OPEN:     #if foo is open, possible states are CLOSED, CANCELED
    ...
if foo.state == STATES.PENDING:  #if foo is pending, possible states are OPEN,CANCELED
    ...

As a result, when foo.state changes to a new state, its set of possible choices changes also.

How can I implement this functionality on Admin add/change pages?

Answer 1

You need to use a custom ModelForm in the ModelAdmin class for that model. In the custom ModelForm's __init__ method, you can dynamically set the choices for that field:

class FooForm(forms.ModelForm):
    class Meta:
        model = Foo

    def __init__(self, *args, **kwargs):
        super(FooForm, self).__init__(*args, **kwargs)
        current_state = self.instance.state
        ...construct available_choices based on current state...
        self.fields['state'].choices = available_choices

You'd use it like this:

class FooAdmin(admin.ModelAdmin):
    form = FooForm

Answer 2

When you create a new admin interface for a model (e.g. MyModelAdmin) there are specific methods for override the default choices of a field. For a generic choice field:

class MyModelAdmin(admin.ModelAdmin):
    def formfield_for_choice_field(self, db_field, request, **kwargs):
        if db_field.name == "status":
            kwargs['choices'] = (
                ('accepted', 'Accepted'),
                ('denied', 'Denied'),
            )
            if request.user.is_superuser:
                kwargs['choices'] += (('ready', 'Ready for deployment'),)
        return super(MyModelAdmin, self).formfield_for_choice_field(db_field, request, **kwargs)

But you can also override choices for ForeignKey and Many to Many relationships.