Question

Hi I have an ajax call which is hooked up with a small view:

def get_spans(snow_load, wind_speed, module_length):
    spans = Spans.objects.values_list('span').filter(
        snow=snow_load,
        wind=wind_speed,
        module_length__gte=module_length,
    ).order_by('span')
    try:
        max_span = max(spans)
    except ValueError:
        max_span = 0
    return max_span

def GetSpans(request):
    # get variables from ajax request
    snow_load = request.GET.get('snow_load', None)
    wind_speed = request.GET.get('wind_speed', None)
    module_length = request.GET.get('module_length', None)
    # call get_spans()
    max_span = get_spans(snow_load, wind_speed, module_length)
    # json encode it
    max_span = simplejson.dumps(max_span, cls=DjangoJSONEncoder)
    return HttpResponse(
        max_span,
        mimetype='application/json'
    )

The problem is that any of these get variables could be '' or decimals. My question is what is the best way to handle these? If the variables are '' I get invalid literal for int() with base 10: errors. Should I replace all empty strings with None for example? Should I cast all values to float?

Any help much appreciated

Answer 1

Filters in django can be chained, so you can do this:

spans = Spans.objects.values_list('span')
if snow_load:
   spans.filter(snow=snow_load)
if wind_speed:
    spans.filter(wind=wind_speed)
if module_length:
    spans.filter(module_length__gte=module_length)

return max(spans.order_by('span'))