Why does grouping by one column return a list of strings instead of a list of dictionaries in SQLModel?

Explanation: The provided code uses the SQLModel library in Python to create a SQLite database and store records in it. The Model class represents the schema of the database table and inherits from the SQLModel class. Two functions, select_groupby_one_col() and select_groupby_more_col(), execute SQL queries using the Session class and the select() method of the sqlmodel library.

The select_groupby_one_col() function should return a list of dictionaries with two keys, 'userId' and 'compl', but it returns a list of strings with only the 'userId' values. In contrast, the select_groupby_more_col() function returns a list of tuples with three values, 'userId', 'year', and 'compl'.

My concern is that, given the implementation of the Model class and the use of the SQLModel library, why does select_groupby_one_col() return a list of strings instead of a list of dictionaries?

from sqlmodel import SQLModel, create_engine, Field, Session, select, func
import random
from pandas import date_range

class Model(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    year: int
    month: int
    userId: str = Field(max_length=10)
    compl: float = Field(...)
    
sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

engine = create_engine('sqlite:///:memory:', echo=True)

def create_db_and_tables():
    SQLModel.metadata.create_all(engine)
    
def create_records():
    
    date_array = date_range(
        start = '2017-01-01',
        periods = 50,
        freq='MS'
    ).date
    list_records = []
    for i,d in enumerate(date_array):
        prod_dict = Model(
            year = d.year,
            month = d.month,
            userId=f'W00000000{random.randint(1,5)}',
            compl = i,
        )
        list_records.append(prod_dict)
    with Session(engine) as session:
        session.bulk_save_objects(list_records)
        session.commit()
        
def select_groupby_one_col():
    with Session(engine) as session:
        statement = select(
            Model.userId,
        ).group_by(
            Model.userId
        )
        statement = statement.add_columns(
            func.sum(Model.compl)
        )
        results = session.exec(statement).all()

        return results 
    
def select_groupby_more_col():
    with Session(engine) as session:
        statement = select(
            Model.userId,
            Model.year
        ).group_by(
            Model.userId
        )
        statement = statement.add_columns(
            func.sum(Model.compl)
        )
        results = session.exec(statement).all()

        return results 
    
def main():
    create_db_and_tables()
    create_records()
    one_col_results = select_groupby_one_col()
    more_col_results = select_groupby_more_col()
    print(one_col_results)
    print(more_col_results)
    

if __name__ == "__main__":
    main()
        

the prints are:

['W000000001', 'W000000002', 'W000000003', 'W000000004', 'W000000005']
[('W000000001', 2017, 109.0), ('W000000002', 2017, 386.0), ('W000000003', 2018, 332.0), ('W000000004', 2017, 148.0), ('W000000005', 2017, 250.0)]

source https://stackoverflow.com/questions/76114759/why-does-grouping-by-one-column-return-a-list-of-strings-instead-of-a-list-of-di