Code to reproduce a probable issue within django-rest-framework. A Place may have many acronyms. The reverse fk relationship ('acronyms') is serialized with a nested AcronymSerializer. When issuing PUT to edit the place, the old acronyms not in the json payload anymore, are not removed from the DB. The HTML form shows the error: non_field_errors…

places.py

## Models
class Place(models.Model):
    name = models.CharField(max_length=255, blank=True)
    slug = models.SlugField(max_length=255, null=True, blank=True)

class PlaceAcronym(models.Model):
    place = models.ForeignKey('Place', related_name="acronyms")
    acronym = models.CharField(_("acronym"), max_length=128,
        help_text=_("An acronym for the place, e.g. 'PV'")
    )


## Detail View
class PlaceDetail(generics.RetrieveUpdateDestroyAPIView):
    model = Place
    serializer_class = PlaceSerializer


## Serializers
class AcronymSerializer(serializers.ModelSerializer):
    def get_identity(self, data):
        return data

    def to_native(self, value):
        return '%s' % (value.acronym, )

    def from_native(self, data, files):
        value =  super(AcronymSerializer, self).from_native({'acronym': data}, files)
        return value


    class Meta:
        model = PlaceAcronym
        fields = ('acronym',)


class PlaceSerializer(serializers.ModelSerializer):
    acronyms = AcronymSerializer(many=True, allow_add_remove=True)

    class Meta:
        model = Place
        view_name = 'maps:place-detail'
        lookup_field = 'slug'
        _self = serializers.HyperlinkedIdentityField(view_name='maps:place-detail')
        fields = (
            '_self',
            'slug', 'name', 'acronyms',
        )

Acronyms are not specified by ID, so the AcronymSerializer needs to override the get_identity hook, and use

return data.get('acronym', None)

instead of

return data.get('id', None)

Acronyms are not specified by ID, so the AcronymSerializer needs to override the get_identity hook, and use

return data.get('acronym', None)

instead of

return data.get('id', None)