Django rest framework foreign key constraint fails creating model

Question

I have the following in a Django Rest Framework setup:

models.py:

class Sku(BaseModel):
    sku_code = models.CharField(max_length=18, primary_key=True)
    supplier_id = models.PositiveIntegerField(db_index=True)
    soh = models.PositiveIntegerField(default=0)
    reserved = models.PositiveIntegerField(default=0)
    broken = models.PositiveIntegerField(default=0)
    unallocated = models.PositiveIntegerField(default=0)
    reorder = models.PositiveIntegerField(default=0)

class Reservation(BaseModel):
    sku = models.ForeignKey(Sku, db_column='sku_code')
    order_id = models.PositiveIntegerField(db_index=True)

serializers.py:

class SkuSerializer(serializers.ModelSerializer):
    class Meta:
        model = Sku
        fields = (
            'sku_code',
            'supplier_id',
            'soh',
            'reserved',
            'broken',
            'unallocated',
            'reorder',
            'created_at',
            'modified_at',
        )


class ReservationSerializer(serializers.ModelSerializer):
    sku = SkuSerializer(read_only=True)

    class Meta:
        model = Reservation
        fields = (
            'id',
            'order_id',
            'sku',
            'created_at',
            'modified_at'
        )

views.py:

class ReservationList(mixins.CreateModelMixin,
                      generics.GenericAPIView):

    queryset = Reservation.objects.all()
    serializer_class = ReservationSerializer

    def post(self, request, *args, **kwargs):
        sku = get_object_or_404(Sku, sku_code=request.data['sku_code'])
        request.data['sku'] = sku
        return self.create(request, *args, **kwargs)

Now when I post to the url linked to ReservationList.post view above I get the error: IntegrityError: (1048, "Column 'sku_code' cannot be null").

It seems to be bypassing the serializers validation and failing on the database layer. For some reason it doesn't accept the SKU being passed in.

What am I doing wrong here? I have tried to follow the example at http://www.django-rest-framework.org/api-guide/relations/#nested-relationships but this seems to break down with the CreateModelMixin. I can't tell if there is something wrong with how my models or serializers are set up.

vikki · Accepted Answer · 2015-10-13 13:18:26Z

4

You've set the sku field to read only, that's why the serializer is ignoring it when you post.

From the relevant documentation

Read-only fields are included in the API output, but should not be included in the input during create or update operations. Any 'read_only' fields that are incorrectly included in the serializer input will be ignored.

answered Oct 13, 2015 at 13:18

vikki

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3 Comments

nicja Over a year ago

Arg, so annoying that I didn't spot this. I had made it read_only as it should not be updated, but needs to be set at creation time. Do you know if there is a way to handle this type of scenario, or would I need to cater for it specifically?

Roba Over a year ago

Overwrite get_serializer() in the view and there test the method - if it's create then remove the field from the read-only fields (_meta class). Or, perhaps cleaner, overwrite get_serializer_class and return a different serializer when creating objects then when updating them.

vikki Over a year ago

@nicja yeah just do it manually. Remove the read_only arg and add required=False then make sure the serializer doesn't receive the sku during updates.

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