Issue with find_one_and_update when including sort key and excluding _id

[val500]

When including a sort key to the find_one_and_update function, while excluding the "_id" with a projection, find_one_and_update will find the document with sorting, but will update a different document. Here's a short script to demonstrate this behavior:

import mongomock


class MongoClientMock(mongomock.MongoClient):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def start_session(self, *args, **kwargs):
        return super().start_session(*args, **kwargs)


def without_id():
    print("without id")
    mock_mongo = MongoClientMock()
    mock_mongo.db.my_collection.insert_one(
        {"field1": "mydata", "field2": 10},
    )
    mock_mongo.db.my_collection.insert_one(
        {"field1": "mydata", "field2": 20},
    )

    # This is the document that is found with this query
    found_response = mock_mongo.db.my_collection.find_one_and_update(
        {"field1": "mydata"},
        {"$set": {"field1": "mynewdata"}},
        projection={
            "_id": False,
        },
        sort=[("field2", -1)],
    )
    print(found_response)

    # This is the document that was updated by the previous query
    updated_response = mock_mongo.db.my_collection.find_one(
        {"field1": "mynewdata"}
    )
    print(updated_response)
    # These documents should be the same but are different


def with_id():
    print("with id")
    mock_mongo = MongoClientMock()
    mock_mongo.db.my_collection.insert_one(
        {"field1": "mydata", "field2": 10},
    )
    mock_mongo.db.my_collection.insert_one(
        {"field1": "mydata", "field2": 20},
    )
    found_response = mock_mongo.db.my_collection.find_one_and_update(
        {"field1": "mydata"},
        {"$set": {"field1": "mynewdata"}},
        sort=[("field2", -1)],
    )
    print(found_response)

    updated_response = mock_mongo.db.my_collection.find_one(
        {"field1": "mynewdata"}
    )
    print(updated_response)
    # These documents are the same as expected when _id is included


if __name__ == "__main__":
    without_id()
    with_id()

[val500]

I believe it is because this query only gets reupdated if "_id" is found in that document:

mongomock/mongomock/collection.py

Line 1368 in d821f32

if old and '_id' in old: