Pydantic v1.10 handle _id with extended BaseModel

schemas.py

from pydantic import BaseModel, root_validator

# NOTE: this works (for me) with pydantic==1.10.13, 
#   but we'll be upgrading to v2 and you can do the same 
#   thing with the model_validator

# considerations:
#   - I'm using this in FastAPI, mostly read-only to my users, 
#     so I don't have a need to keep the ObjectId, and convert
#     back to the bson ObjectId as-needed
class BaselineOverrideID(BaseModel):
    """Inherit this to convert the bson.ObjectID to a string, and
    set the variable name to return using the _id_str_name variable

    USAGE:
        class TestOverride(BaselineOverrideID):
            _id_str_name = "test_id"
            test_id: Optional[str] = "gets_over_written"
            ...
        As long as the dict passed into the constructor for this has an _id,
        it overwrites the test_id default value with the str-equivalent. 

    EXAMPLE:
        test_dict = {"_id": bson.ObjectId("64a3752f7946675e994894df")}
        test_obj = TestOverride.parse_obj(test_dict)

        test_obj.test_id
        >>> "64a3752f7946675e994894df"

        type(test_obj.test_id)
        >>> str
    """
    _id_str_name: str

    # We have to set pre=True since the inheriting objects 
    # likely don't keep the _id field
    @root_validator(pre=True)
    def _set_fields(cls, values: dict) -> dict:
        """This is a validator that converts the _id 
        field into a string with the specified name.

        Args:
            values (dict): Stores the attributes of the extended object.
        """
        if "_id" in values.keys():
            values[cls._id_str_name] = str(values["_id"])
        return values

    
if __name__=="__main__":
    import bson
    class ExampleUser(BaselineOverrideID):
        _id_str_name = "user_id"
        user_id: Optional[str] = None
        email: str
        # ... + more fields

    example_user_d = {
        "_id": bson.ObjectId("63a3752f7946675e994894df"),
        "email": "sam@uptrends.ai"
    }
    example_no_id_user_d = {
        "email": "idk@internet.xyz"
    }
    
    example_user = ExampleUser(**example_user_d)
    example_no_id_user = ExampleUser(**example_no_id_user_d)
    print(f"user w/ id:  type(user_id)=={type(example_user.user_id)} ({example_user.user_id})")
    print(f"user w/o id: type(user_id)=={type(example_no_id_user.user_id)} ({example_no_id_user.user_id})")
    """OUTPUT >>
    user w/ id:  type(user_id)==<class 'str'> (63a3752f7946675e994894df)
    user w/o id: type(user_id)==<class 'NoneType'> (None)
    """