Use marshmallow-sqlalchemy to deserialize the object, but an error occurred. I have passed the session object, which is a database DB, but still no effect, this problem has been 2 days, still can not solve.

my_db.py

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, scoped_session

DATABASE_URL = "mysql+pymysql://root:Cfzy2018!@xxxxx:xxxx/fastapi"
engine = create_engine(DATABASE_URL, echo=True)
SessionLocal = sessionmaker(
    bind=engine,
    autocommit=False,
    autoflush=False,
    expire_on_commit=False
)
my_session = scoped_session(SessionLocal)

Base = declarative_base()

Base.metadata.create_all(bind=engine)

def get_db():
    session_db = my_session()
    try:
        yield session_db
    except Exception as e:
        logger.error("Exception info: %s", str(e))
        session_db.rollback()
        raise e
    finally:
        session_db.close()

song.py

@app.post("/create_song_sheet/")
async def create_song_sheet(request: Request, db: Session = Depends(get_db)):
    user_dict = request.state.user  # user_dict_data
    user: UserDB = UserSchema().load(user_dict, session=db)

    # other code
    return {"status": "success", "data": user}

my_schemas.py

class SongSchema(SQLAlchemySchema):

class Meta:
    model = SongDB
    load_instance = True
    include_relationships = True

My code should be working, but I don’t know what the problem is.