How to use a transaction in a stored procedure? - mysql

Question

I have an SQL script that I need to convert to a parameterized stored procedure. I've only written simple functions in the past, never a complex transactional query with parameters.
Any help is greatly appreciated - simplified queries below. This script could really be anything containing a transaction and some user inputs.
-- transaction ensures i can clean up a mess, if one happens
begin;
-- parameters for the script; currently set manually before execution
set #parent_id := 123;
set #identifier := 'someid';
-- insert some row with user-specified values
insert into users (field1, field2) values (#parent_id, #identifier);
-- get the new id
set #user_id := last_insert_id();
-- do another insert
insert into usersmeta (user_id, field1, field2) values (#user_id, 1, 2);
-- if no errors happened yet, commit transaction
commit;
-- "return value"; some select query (could be 1 or many rows)
select users.id userid, usersmeta metaid
from users
join usersmeta on usersmeta.user_id = users.id;
I started with but then I pretty much got stuck. I'm especially concerned with ensuring errors, in the event they occur, are somehow made visible to the calling code
delimiter ;;
CREATE PROCEDURE mytask(IN parent_id INT(11), IN identifier VARCHAR(200))
BEGIN
SET #query = ???
PREPARE q FROM #query;
EXECUTE q;
DEALLOCATE PREPARE q;
END;;
delimiter ;

Answer 1

It took a good amount of research, trial, and error, but I think I arrived at a pretty good solution.
DELIMITER //
CREATE PROCEDURE my_procedure (IN parent_id int, IN identifier varchar(255), OUT out_user_id int)
BEGIN
-- local variable, set later after user is created
DECLARE user_id int;
-- rollback transaction and bubble up errors if something bad happens
DECLARE exit handler FOR SQLEXCEPTION, SQLWARNING
BEGIN
ROLLBACK;
RESIGNAL;
END;
START TRANSACTION;
-- insert some row with user-specified values
INSERT INTO users (field1, field2) values (parent_id, identifier);
-- get the new id
SET user_id = last_insert_id();
-- do another insert
INSERT INTO usersmeta (user_id, field1, field2) values (user_id, 1, 2);
-- if no errors happened yet, commit transaction
COMMIT;
-- return
SELECT user_id INTO out_user_id;
END //
DELIMITER ;
I can use it like this
-- run the procedure
CALL my_procedure(123, 'some_id', #user_id);
-- get the "return" value
SELECT #user_id as user_id;
This is definitely the most complex stored procedure I've written. If anyone sees an area for improvement, I'd be happy to learn how I can make it better.