Dynamic serializer fields are not supported

[melvinkcx]

Hi, I'm trying to use a serializer that adds fields dynamically. However, XLSXRenderer is not able to pick up those fields.

Here's a simple example:

class MySerializer(serializers.Serializer):
    field_1 = serializers.CharField()

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields["dynamic_field_1"] = serializers.CharField(label="Dynamic Field", allow_null=True)

In the output XLSX, only field_1 is included.

I believe the use of serializer.get_fields() is the root cause:

drf-excel/drf_excel/renderers.py

Line 277 in 0d47d7b

_fields = serializer.get_fields()

The default implementation of get_fields() in BaseSerializer returns self._declared_fields. This can be resolved by referencing to serializer.fields instead.

Let me know what you think. I can create an MR to fix it.

IMO, I think we should update this line to use serializer.fields as well.

https://github.com/django-commons/drf-excel/blob/0d47d7bdfcfbe8d09e6186bfea46f8cdc76e2adc/drf_excel/renderers.py#L156C18-L156C29

[browniebroke]

Interesting... Didn't know it was a thing, is it something well supported by DRF? I'm wondering if there would be any unintended side effects. If you can make a PR with some good testing, I'll be happy to look into it, yes.

[FlipperPA]

There's another reference to get_fields() here:

drf-excel/drf_excel/renderers.py

Line 244 in 0d47d7b

for k, v in serializer.get_fields().items():

We should review and make sure there wouldn't be side-effects there.

[rptmat57]

I thought serializer.fields was already calling get_fields() anyway... but I might be wrong, I haven't looked at that code in a bit.

[melvinkcx]

@rptmat57 you're right. serializer.fields is calling get_fields(). However, if extra fields are being added dynamically to serializer.fields in the constructor, get_fields() of the BaseSerializer will not be able to include them. Hence, I think it'd be better to retrieve all fields with serializer.fields rather than serializer.get_fields()