Error when accessing serializer.data that contains price-related fields (For example, CheckoutSerializer)

[rollue]

I overrode the checkoutserializer(added an extra sender_info field), so I was writing some tests on the serializer itself.

# test_serializers.py
...
cs = CheckoutSerializer(data=payload, context={"request": request})
cs.is_valid(raise_exception=True)
data = cs.data  <- error raised
...

The raised error was decimal.InvalidOperation: [<class 'decimal.ConversionSyntax'>].

I error message was not clear at first, so I did some digging in, and I found that the error was raised within the serializer's to_representation block.

...
# django-rest-framework(=3.10.3)'s serializers.py
...
...
check_for_none = attribute.pk if isinstance(attribute, PKOnlyObject) else attribute
if check_for_none is None:
    ret[field.field_name] = None
else:
    ret[field.field_name] = field.to_representation(attribute)  <- error here line 526

It seems the attribute is Price class return by the following line, in oscarapi's checkoutserializer's validate method.

total = OrderTotalCalculator().calculate(basket, shipping_charge)

So the attribute looks like this:

Price(currency='USD', excl_tax=Decimal('10000.00'), incl_tax=Decimal('10000.00'), tax=Decimal('0.00'))

So in order to access the serializer.data, one might have to handle decimal fields(total in this checkoutserializer) individually by using attribute.incl_tax as a parameter to to_representation method, when dealing with price-related fields. Or you can probably handle this at field level too.

This error may be trivial because it does NOT affect the core logic and purpose of the CheckoutSerializer - so this may not have to be fixed.

But I'm leaving this issue as a reference for someone who might need to access serializer.data like me. :) (FYI, you can still access serializer.validated_data without any extra error handling)

[maerteijn]

It indeed looks like the OrderTotalCalculator is returning a Price object and not a Decimal value.

My first thought is that the current CheckoutSerializer total field definition is wrong and should be replaced by a PriceSerializer

But I need more investigation for this, thanks for reporting!

[maerteijn]

As already thought, the input type for the total field is a Decimal, in the validate method we change this to a Price instance returned by the OrderTotalCalculator. We should not do this, see the pull request.

BTW, accessing the data attribute is a bit funky here as the CheckoutSerializer does not really fit into the normal" Django Rest Framework serializing objects" way of working.

See also the comment by Tom Christie.

Access validated_data instead, (which was also broken but fixed with this pull request)

[maerteijn]

@mhoonjeon The pull request is merged, see the comments above. Thanks you your input, closing this issue now

[rollue]

@maerteijn Sorry I checked this feedback a little late; I use gitlab for work most of the times and I only check github from time to time :(. Anyways, thanks for the feedback and I really appreciate how much you guys have put into this open source project. Keep up the good work!!