Filtering records by incrementing parameters in Django

Question

I've been able to implement a filtering solution for my app...so far I have filtering by year, make and body style for a vehicle inventory. What I want to do is to filter the record this way:

Lets assume I choose Acura in make, in the resultant page, if I choose one of the other filters i.e. year or body style, I'll need only the records containing Acura and the chosen year or body style.

My code for one of the filters is as below:

def year_filter(request, year):   
   vehicle_query = Vehicle.objects.filter(
 common_vehicle__year__year__exact=year
 ).exclude(status__status='Incoming')

   vehicle_list = vehicle_query.order_by(
 'common_vehicle__series__model__manufacturer__manufacturer', 
 'common_vehicle__series__model__model', 
 'common_vehicle__year'
)

   vehicle = paginate(request, vehicle_list)

   year_count = vehicle_query.order_by(
 '-common_vehicle__year__year')
            .values('common_vehicle__year__year')
            .annotate(count=Count('id')
   )
   make_count = vehicle_query.order_by(
      'common_vehicle__series__model__manufacturer__manufacturer')
      .values('common_vehicle__series__model__manufacturer__manufacturer')
      .annotate(count=Count('id')
)
    style_count = vehicle_query.order_by(
   'common_vehicle__body_style__style')
       .values('common_vehicle__body_style__style')
       .annotate(count=Count('id')
)
    color_count = vehicle_query.order_by(
       'exterior_colour__exterior_colour')
       .values('exterior_colour__exterior_colour')
       .annotate(count=Count('id')
)

    return render_to_response('vehicles.html', {
      'vehicle': vehicle, 
      'make_count': make_count, 
      'year_count': year_count, 
      'style_count': style_count,
    })

Answer 1

Firstly, some style advice: you're making four separate queries, but each of them start in exactly the same way:

Vehicle.objects.filter(
   common_vehicle__series__model__manufacturer__manufacturer=make
).exclude(
   status__status='Incoming'
)

For the sake of readability, please consider assigning this to a variable, eg vehicle_query, which you can then use in each subsequent query:

vehicle_list = vehicle_query.order_by(
   'common_vehicle__series__model__manufacturer__manufacturer', 
   'common_vehicle__series__model__model', 
   'common_vehicle__year'
)

The query isn't evaluated until the last minute, so this won't affect efficiency, but will be much more readable.

Now, to answer your question: you'll obviously need some way of saving the chosen values from one view to the next. I can't quite understand how the other views fit with this one - my initial inclination would be to put it in a hidden field, or in the querystring. But maybe saving it in the session would be the best idea:

if request.POST:
    chosen_vehicle = request.POST['vehicle_type']
    request.session['vehicle_type'] = chosen_vehicle.id
    return HttpResponseRedirect('/next/view/')

and in the next view:

previously_chosen = request.session['vehicle_type']
filtered = Vehicle.objects.get(id=previously_chosen)

Does that work?