Nested serializer source argument fails silently: field missing

[dennisvang]

This looks like a bug, but maybe there's some documentation that I missed.

Suppose I have a model serializer with a field based on a nested serializer:

class MyModelSerializer(serializers.ModelSerializer):
    class Meta:
        model = MyModel
        fields = ('my_field')

    my_field = BarSerializer(
        source='foo.bar_set', many=True, read_only=True
    )

Normally this works.

However, there are (afaik) two cases in which my_field is completely omitted from the serialized data:

• if there is a typo in the source argument (e.g. I erroneously tried to use django lookup syntax: 'foo__bar_set')
• if there is no related foo object, i.e. if MyModel.foo is None

There is no error to warn about the missing field.

Using DRF 3.15.2 on windows 10 or linux, python 3.11.

Also see here.

[lovelydinosaur]

https://github.com/encode/django-rest-framework/blob/master/rest_framework/fields.py#L431

I had to remind myself from the source what's going on here. Looks like you'll get an error if the field is required otherwise it'll be omitted. I'd suggest this neither is nor isn't a bug, it's just fuzzy behavior.

[dennisvang]

@tomchristie Thanks for looking into this!

For me it was quite surprising that the entire field is omitted, instead of e.g. including the field with a value of None.

This caused a bug in my code, which, imho, would have been much easier to track down if there had been a warning or error message.

Anyway, thank you for creating this wonderful thing called DRF!