In PYTHON-4550, we accidentally added this API to UpdateResult:

class UpdateResult(_WriteResult):
...
    @property
    def did_upsert(self) -> bool:
        """Whether or not an upsert took place."""
        assert self.__raw_result is not None
        return len(self.__raw_result.get("upserted", {})) > 0

did_upsert is unnessecary because an app can already check for an upsert like this: res.upserted_id is not None

I'm also suspicious of the in_client_bulk flag that was added to UpdateResult and any logic that depends on it.

Originally reported here: https://www.mongodb.com/community/forums/t/pymongo-bug-updateresult-did-upsert-throws/298787/1

I'm using pymongo 4.9.1 with a local, docker-deployed atlas install of MongoDB 7.0.12.

MRE:

from pymongo import MongoClient

mc = MongoClient(directConnection=True)

# Record to be upserted just needs to not already exist
update_result = mc.mydatabase.mycollection.update_one(
    {"hi": 55, "ok": 10},
    {"$set": {"well": 55}},
    upsert=True,
)

update_result.did_upsert
Evaluating did_upsert throws because:

python3.10/site-packages/pymongo/results.py", line 176, in did_upsert
      return len(self.__raw_result.get("upserted", {})) > 0
  TypeError: object of type 'ObjectId' has no len()
As the error implies, self.__raw_result["upserted"] is a bson.objectid.ObjectId.

Seems like a very straightforward bug to me. Let me know if you need any more information.