Django Rest Framework OneToOneField相关的BooleanFilter

Question

I'm using django with rest-framework.

Now I have models with OneToOne relations:

class ModelA(models.Model):
    pass

class ModelB(models.Model):
    a = models.OneToOneField(
        A, related_name='b')

And I have a ViewSet applied on A:

class ModelAViewSet(viewsets.ModelViewSet):
    queryset = ModelA.objects.all()
    serializer_class = ModelASerializer

Then, I want to add a BooleanFilter on ModelAViewSet to filter whether the ModelA object has a relating ModelB object.

And I tried the below:

class ModelAViewSet(viewsets.ModelViewSet):
    class Filter(FilterSet):
        has_b = filters.BooleanFilter('b')
    queryset = ModelA.objects.all()
    serializer_class = ModelASerializer
    filter_fields = ['has_b']

So, if it works, we got:

1. ?has_b=1 : returning all records without filtering;
2. ?has_b=2 : returning records which have relating ModelA object;
3. ?has_b=3 : returning records which NO NOT have relating ModelA object;

It almost worked, except the case 3 above.

So what's the correct way to do this?

Answer 1

from django_filters.rest_framework import FilterSet, filters

class Filter(FilterSet):
    has_b = filters.BooleanFilter(name='b', lookup_expr='isnull', exclude=True)

There are three changes here:

1. By importing from the rest_framework sub-package, an API-friendly BooleanWidget is used, so you can query ?has_b=true instead of ?has_b=1 .

2. The filter is using an isnull lookup, which allows you to test for existence of a related model.

3. b__isnull=True is testing for the lack of a related B , which is the opposite of what you want. Using exclude=True reverses the logic such that you instead filter for A s that have a related B instead.

The equivalent .filter() calls:

# before, incorrect
A.objects.filter(b=True)

# after, correct
A.objects.exclude(b__isnull=True)