sqlalchemy error when calling mysql stored procedure

Question

I'm using sqlalchemy to run query on a MySql server from python.

I initialize sqlalchemy with:

engine = create_engine("mysql+mysqlconnector://{user}:{password}@{host}:{port}/{database}".format(**connection_params))
conn = engine.connect()

Where connection_params is a dict containing the server access details.

I'm running this query:

SELECT 
new_db.asset_specification.identifier_code, 
new_db.asset_specification.asset_name, 
new_db.asset_specification.asset_type, 
new_db.asset_specification.currency_code, 
new_db.sector_map.sector_description, 
new_db.super_sector_map.super_sector_description, 
new_db.country_map.country_description, 
new_db.country_map.country_macro_area 

FROM new_db.asset_specification 
INNER JOIN new_db.identifier_code_legal_entity_map on new_db.asset_specification.identifier_code = new_db.identifier_code_legal_entity_map.identifier_code 
INNER JOIN new_db.legal_entity_map on projecthf_db.identifier_code_legal_entity_map.legal_entity_code = new_db.legal_entity_map.legal_entity_code 
INNER JOIN new_db.sector_map on new_db.legal_entity_map.legal_entity_sector = new_db.sector_map.sector_code 
INNER JOIN new_db.super_sector_map on projecthf_db.legal_entity_map.legal_entity_super_sector = new_db.super_sector_map.super_sector_code 
INNER JOIN new_db.country_map on new_db.legal_entity_map.legal_entity_country = new_db.country_map.country_code 
WHERE new_db.asset_specification.identifier_code = str_identifier_code;

Using conn.execute(query) (where i set query equal to the string above).

This runs just fine.

I tried to put my query in a stored procedure like:

CREATE DEFINER=`root`@`localhost` PROCEDURE `test_anag`(IN str_identifier_code varchar(100))
BEGIN
SELECT 
new_db.asset_specification.identifier_code, 
new_db.asset_specification.asset_name, 
new_db.asset_specification.asset_type, 
new_db.asset_specification.currency_code, 
new_db.sector_map.sector_description, 
new_db.super_sector_map.super_sector_description, 
new_db.country_map.country_description, 
new_db.country_map.country_macro_area 

FROM new_db.asset_specification 
INNER JOIN new_db.identifier_code_legal_entity_map on new_db.asset_specification.identifier_code = new_db.identifier_code_legal_entity_map.identifier_code 
INNER JOIN new_db.legal_entity_map on projecthf_db.identifier_code_legal_entity_map.legal_entity_code = new_db.legal_entity_map.legal_entity_code 
INNER JOIN new_db.sector_map on new_db.legal_entity_map.legal_entity_sector = new_db.sector_map.sector_code 
INNER JOIN new_db.super_sector_map on projecthf_db.legal_entity_map.legal_entity_super_sector = new_db.super_sector_map.super_sector_code 
INNER JOIN new_db.country_map on new_db.legal_entity_map.legal_entity_country = new_db.country_map.country_code 
WHERE new_db.asset_specification.identifier_code = str_identifier_code;

END

I can run the stored procedure from the query editor in mysql workbench with CALL new_db.test_anag('000000') and I get the desired result (which is a single line).

Now I try to run:

res = conn.execute("CALL new_db.test_anag('000000')")

But it fails with the following exception

sqlalchemy.exc.InterfaceError: (mysql.connector.errors.InterfaceError) Use multi=True when executing multiple statements [SQL: "CALL projecthf_db.test_anag('0237400')"]

I looked around but I can't find anything useful on this error and for the love of me I can't get my head around it. I'm not an expert on either Mysql nor sqlalchemy (or anything RDBMS) but this one looks like it should be easy to fix. Let me know if more info is required.

Thank in advance for the help

Answer 1

From reading a related question it can be seen that mysql.connector automatically fetches and stores multiple result sets when executing stored procedures producing such, even if only one result set is produced. SQLAlchemy on the other hand does not support multiple result sets – directly. To execute stored procedures use callproc(). To access a DB-API cursor in SQLAlchemy you have to use a raw connection. In case of mysql.connector the produced result sets can be accessed using stored_results():

from contextlib import closing

# Create a raw MySQLConnection
conn = engine.raw_connection()

try:
    # Get a MySQLCursor
    with closing(conn.cursor()) as cursor:
        # Call the stored procedure
        result_args = cursor.callproc('new_db.test_anag', ['000000'])
        # Iterate through the result sets produced by the procedure
        for result in cursor.stored_results():
            result.fetchall()

finally:
    conn.close()