Django model choice field - depend on other field's choice

Question

I need django modelform with 2 fields, where second field choice list depends on what was chosen in first one. My model:

class Offer(BaseModel):

    VEHICLE_TYPES = (
        ('personal','Personal car'),
        ('truck','Truck'),
    )
    vehicle_type = models.CharField(max_length=32, choices=VEHICLE_TYPES, default='personal', verbose_name='Vehicle type')

    PERSONAL_MAKES = (
        ('',''),
    )
    TRUCK_MAKES = (
        ('',''),
    )
    make = models.CharField(max_length=32)#what more??

How can I set choices of make field to PERSONAL_MAKES if vehicle_type is set to personal? How can I do this? Is it possible on model level?

Answer 1

You probably can't because it depends of user interaction with your form: your server can't know in advance which element your user will select before sending the form to the browser. You could probably achieve this using ajax. I think a working process could be :

• Create a form with all the fields, and make make field hidden
• Create a view (I'll call it AjaxMakeFieldView) that will catch an ajax request taking a vehicle_type argument and return the HTML for make field, populated with relevant data. Add a URL in your URLConf for this view.
• In your template, add a Javascript binding : when user select a vehicle_type, the browser will send aan ajax request to AjaxMakeFieldView and replace hidden make field with returned HTML

If you don't want javascript, another way would be a two step form :

• A first form with a vehicle_type field
• Once the first form is submitted, your user get a second form with a make field, which initial data is populated depending of vehicle_type selected in the first form.

I've never done this, but Django documentation on Form wizard seems a good place to start.