can't patch nested values from django rest framework

Question

I am trying to develop a REST API with django-rest-framework for updating a django model.

I want to unit test it with the following unit test

from rest_framework.test import APITestCase
class PatchInvestmentTest(APITestCase):

    def test_repartition(self):

        investment = Investment.objects.create()
        sponsor1 = Investment.objects.create(InvestmentSponsor, name='A')
        sponsor2 = Investment.objects.create(InvestmentSponsor, name='B')

        url = reverse('investments:investments-detail', args=[investment.id])
        data = {
            'sponsorships': [
                {'sponsor': sponsor1.id, 'percentage': 80},
                {'sponsor': sponsor2.id, 'percentage': 10},
            ]
        }

        print("> data", data)

        response = self.client.patch(url, data=data)

        self.assertEqual(response.status_code, status.HTTP_200_OK)

        self.assertEqual(1, Investment.objects.count())
        investment = Investment.objects.all()[0]
        # It fails below : no investments are created
        self.assertEqual(len(investment.sponsorships()), 2)

The model can be summed up with

class Investment(models.Model):
    # ... a few fields

    def sponsorships(self):
        return self.investmentsponsorship_set.all().order_by('sponsor__ordering', 'sponsor__name')


class InvestmentSponsor(models.Model):
    name = models.CharField(max_length=200, verbose_name=_('name'))
    ordering = models.IntegerField(default=0)

    class Meta:
        ordering = ('ordering', 'name', )


class InvestmentSponsorship(models.Model):
    sponsor = models.ForeignKey(InvestmentSponsor)
    investment = models.ForeignKey(Investment)
    percentage = models.DecimalField(max_digits=5, decimal_places=2)

The api is using rest-framework base classes

class InvestmentViewSet(viewsets.ModelViewSet):
    model = Investment

    def get_serializer_class(self):
        serializers_class_map = {
            'default': InvestmentSerializer,
            'partial_update': PartialUpdateInvestmentSerializer,
        }
        return serializers_class_map.get(self.action, serializers_class_map['default'])

    def perform_update(self, serializer):
         serializer.save()

Then I expect to get and handle the "sponsorhips" data in the serializers

class InvestmentSponsorshipSerializer(serializers.ModelSerializer):

    class Meta:
        model = models.InvestmentSponsorship
        fields = ('sponsor', 'percentage', )


class PartialUpdateInvestmentSerializer(serializers.ModelSerializer):
    sponsorships = InvestmentSponsorshipSerializer(many=True)

    class Meta:
        model = models.Investment
        fields = (
            'id', '... others', 'sponsorships',
        )

    def validate_sponsorships(self, value):
        print("validate_sponsorships", value)
        return value

    def update(self, instance, validated_data):
        """update only fields in data"""

        data = validated_data.copy()

        print("*** DATA", validated_data)

        instance.save()

        return instance

The problem is that the data I received from the serializer is empty

 > data {'sponsorships': [{'sponsor': 1, 'percentage': 80}, {'sponsor': 2, 'percentage': 10}]}
 validate_sponsorships []
 *** DATA {'sponsorships': []}

This seems to occur only when unit testing. It seems to work from the dango-rest-framework admin.

I've tried to investigate why I don't received the data as validated_data in the update with no success yet.

Any idea?

Have you tried defining a related_name='sponsorships' for investment foreign key on InvestmentSponsorship model ? (you would have to get rid of the sponsorship method on Investment). If that works, you can had ordering on InvestmentSponsorship Meta. — Michael Rigoni
thanks for suggestion which is valid. Unfortunately, it doesn't change anything for this problem — luc

Michael Rigoni Michael Rigoni · Accepted Answer · 2018-01-17T23:44:36

You should add format parameter when calling patch:

        response = self.client.patch(url, data=data, format='json')

Default multipart format does not support nesting I think.

can't patch nested values from django rest framework

2 Answers