Model serialization drops keys

There may be an issue affecting the serialize_model methods of the Pydantic models in this library.

Taking the DocumentContent model as an example, we see:

class DocumentContent(BaseModel):
    full_text_list: Annotated[
        Optional[List[str]], pydantic.Field(alias="fullTextList")
    ] = None
    r"""The plaintext content of the document."""

    @model_serializer(mode="wrap")
    def serialize_model(self, handler):
        optional_fields = set(["fullTextList"])
        serialized = handler(self)
        m = {}

        for n, f in type(self).model_fields.items():
            k = f.alias or n
            val = serialized.get(k)

            if val != UNSET_SENTINEL:
                if val is not None or k not in optional_fields:
                    m[k] = val

        return m

This model uses a field alias that, when constructing the Pydantic object from an API response, will map the fullTextList field of the JSON object to the full_text_list field of the Pydantic object.

However, the model serializer uses:

...
k = f.alias or n
val = serialized.get(k)
...

which means that the field alias (fullTextList) will be used to extract the value rather than the Pydantic field name. This results in value being None and in missing keys in the returned dictionary m when the field name and its alias are different.

To support this claim, please find attached a documents.json file that contains an anonymized response collected from the Glean API (/rest/api/v1/getdocuments endpoint).

And below is a simple debug.py script to run alongside it:

import pathlib

from glean.api_client import models
from glean.api_client.utils.unmarshal_json_response import unmarshal_json_response


class DummyHttpResponse:
    def __init__(self, text):
        self.status_code = 200
        self.text = text


with pathlib.Path("documents.json").open("r") as f:
    http_res = DummyHttpResponse(
        text=f.read(),
    )


documents_response = unmarshal_json_response(models.GetDocumentsResponse, http_res)


assert isinstance(documents_response, models.GetDocumentsResponse)
assert documents_response.documents is not None
assert isinstance(
    documents_response.documents["https://company.com/Test"].content,
    models.DocumentContent,
)
assert (
    documents_response.documents["https://company.com/Test"].content.full_text_list[0]
    == "This is a test document."
)

serialized_document_response = documents_response.model_dump()

assert isinstance(serialized_document_response, dict)
assert serialized_document_response["documents"] is not None

# Here's the problem: no `full_text_list` or `fullTextList` in the serialized response!
assert (
    len(serialized_document_response["documents"]["https://company.com/Test"]["content"])
    > 0
)

Running it yields:

$ ls    
debug.py  documents.json

$ python debug.py
Traceback (most recent call last):
  File "/workspace/app/debug/debug.py", line 40, in <module>
    len(serialized_document_response["documents"]["https://company.com/Test"]["content"])
    > 0
AssertionError

Note that I'm using:

pydantic_core==2.41.5
pydantic==2.12.5
glean-api-client==0.11.27

Start with src/glean/api_client/models/documentcontent.py and inspect serialize_model, then run debug.py with documents.json through unmarshal_json_response. Done means the serialized DocumentContent content is non-empty and includes the affected field, as checked by the assertions in debug.py.