Django Rest Framework filtering calculated model property

Question

Sorry for a newbie question. I have a following model:

class WeightSlip(models.Model):

    grossdate = models.DateTimeField(auto_now=False, auto_now_add=False)
         


        

Answer 1

You can create custom filter for slipdate, netweight that will evaluate and filter this fields in db. For this you can use conditional expressions and F expression

from django.db.models import F, Case, When

class WeightSlipFilter(FilterSet):
    slipdate = DateTimeFilter(method='filter_slipdate')
    netweight = NumberFilter(method='filter_netweight')

    class Meta:
        model = WeightSlip
        fields = ('slipdate', 'netweight', 'vehicle')

    def filter_netweight(self, queryset, value):
        if value:
            queryset = queryset.annotate(netweight=F('grossweight') - F('tareweight')).filter(netweight=value)
        return queryset

    def filter_slipdate(self, queryset, value):
        if value:
            queryset = queryset.annotate(slipdate=Case(When(grossdate__gt=F('taredate'), then=F('grossdate')), default=F('taredate')).filter(slipdate=value)
        return queryset