narainsagar narainsagar - 5 months ago 30
MySQL Question

How to Store MySQL Trigger exception / failure info into Table or in Variables

I am stuck at somewhere and I need some help from you.

Scenario



I have two databases i.e.,
test_db1
and
test_db2
and have
users
table on both of them. Both databases initially are empty (0 rows).

Here's
users
table schema:

DROP TABLE IF EXISTS `users`;
CREATE TABLE `users` (
`id` int(11) AUTO_INCREMENT,
`name` varchar(30) NOT NULL,
`age` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;


After that, I have written some triggers for
INSERT
,
UPDATE
and
DELETE
events on
test_db1.users
table, Below is what each trigger does:


  • on
    INSERT
    in
    test_db1.users
    , insert same row in
    test_db2.users

  • on
    UPDATE
    in
    test_db1.users
    , update same row in
    test_db2.users

  • on
    DELETE
    in
    test_db1.users
    , delete same row from
    test_db2.users



And here's the trigger code snippet.

DELIMITER //

-- TRIGGER FOR INSERT
DROP TRIGGER IF EXISTS `test_db1_users_bi`;
CREATE TRIGGER `test_db1_users_bi` BEFORE INSERT ON `users` FOR EACH ROW
BEGIN
INSERT INTO `test_db2`.`users` (id, name, age) VALUES (NEW.id, NEW.name, NEW.age);
END; //

-- TRIGGER FOR UPDATE
DROP TRIGGER IF EXISTS `test_db1_users_bu`;
CREATE TRIGGER `test_db1_users_bu` BEFORE UPDATE ON `users` FOR EACH ROW
BEGIN
UPDATE `test_db2`.`users`
SET name = NEW.name,
age = NEW.age
WHERE id = NEW.id;
END; //

-- TRIGGER FOR DELETE
DROP TRIGGER IF EXISTS `test_db1_users_bd`;
CREATE TRIGGER `test_db1_users_bd` BEFORE DELETE ON `users` FOR EACH ROW
BEGIN
DELETE FROM `test_db2`.`users`
WHERE id = OLD.id;
END; //

-- DELIMITER;


Now, the Question!

Currently, this doesn't have any errors/exceptions handlers defined in triggers.. So, I want to handle that too but I don't know how to do that. I just don't know how would I get the exception and it's properties like exceptions - error code, error message?

I just want to store the caught exception/error into
test_db1
.
errors
table from each of the trigger (if fails):

Here's
errors
table schema something looks like:

DROP TABLE IF EXISTS `errors`;
CREATE TABLE `errors` (
`id` int(11) AUTO_INCREMENT,
`error_code` varchar(30) DEFAULT NULL,
`error_message` TEXT DEFAULT NULL,
`emailed` TINYINT DEFAULT 0,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;


FYI: Below are the possible failures:


  • If
    test_db2
    is not there or unable to connect?

  • If
    INSERT
    trigger fails i.e., whatever the reason?

  • If
    UPDATE
    trigger fails i.e., whatever the reason?

  • If
    DELETE
    trigger fails i.e., whatever the reason?



If anyone can Just let me know how can I get the exception and it's properties like error code, error message and store it to variables from inside triggers so that then I will perform insert to store them into table?

I am running MySQL version: 5.5+

Thanks!

Answer

I found a hack via DECLARE CONTINUE HANDLER and GET DIAGNOSTICS CONDITION, so just thought, I must share it here.

Here's my complete final script which keeps backup (sync) for both databases users table what it means is that any update on test_db1 (which we may call it as a productionDB) will occur on test_db2 (which we may call it to as stagingDB):

/*
Create two databases:
    1. `test_db1`
    2. `test_db2`
and execute below create *Table script* on both databases.
after that execute *Triggers Script* on `test_db1` only..
*/

/*
    TABLE STRUCTURE FOR `users`
*/

DROP TABLE IF EXISTS `users`;
CREATE TABLE IF NOT EXISTS `users` (
  `id` int(11) AUTO_INCREMENT NOT NULL,
  `name` varchar(30) NOT NULL,
  `age` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

/*
    TABLE STRUCTURE FOR `errors`
*/

DROP TABLE IF EXISTS `errors`;
CREATE TABLE IF NOT EXISTS `errors` (
  `id` int(11) AUTO_INCREMENT NOT NULL,
  `code` varchar(30) NOT NULL,
  `message` TEXT NOT NULL,
  `query_type` varchar(50) NOT NULL,
  `record_id` int(11) NOT NULL,
  `on_db` varchar(50) NOT NULL,
  `on_table` varchar(50) NOT NULL,
  `emailed` TINYINT DEFAULT 0,
  `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

/*
    TRIGGERS SCRIPTS FOR INSERT, UPDATE AND DELETE OPERATIONS
*/

DELIMITER //

-- TRIGGER FOR INSERT
DROP TRIGGER IF EXISTS `test_db1_users_ai`;
CREATE TRIGGER `test_db1_users_ai` AFTER INSERT ON `users` FOR EACH ROW 
BEGIN
    -- Declare variables to hold diagnostics area information
    DECLARE errorCode CHAR(5) DEFAULT '00000';
    DECLARE errorMessage TEXT DEFAULT '';

    -- Declare exception handler for failed insert
    DECLARE CONTINUE HANDLER FOR SQLEXCEPTION 
    BEGIN
      GET DIAGNOSTICS CONDITION 1
        errorCode = RETURNED_SQLSTATE, errorMessage = MESSAGE_TEXT;
    END;

    -- Perform the insert
    INSERT INTO `test_db2`.`users` (id, name, age) VALUES (NEW.id, NEW.name, NEW.age);

    -- Check whether the insert was successful
    IF errorCode != '00000' THEN
        INSERT INTO `errors` (code, message, query_type, record_id, on_db, on_table) VALUES (errorCode, errorMessage, 'insert', NEW.id, 'test_db2', 'users');
    END IF;
END; //

-- TRIGGER FOR UPDATE
DROP TRIGGER IF EXISTS `test_db1_users_au`;
CREATE TRIGGER `test_db1_users_au` AFTER UPDATE ON `users` FOR EACH ROW 
BEGIN
    -- Declare variables to hold diagnostics area information
    DECLARE errorCode CHAR(5) DEFAULT '00000';
    DECLARE errorMessage TEXT DEFAULT '';

    -- Declare exception handler for failed insert
    DECLARE CONTINUE HANDLER FOR SQLEXCEPTION 
    BEGIN
      GET DIAGNOSTICS CONDITION 1
        errorCode = RETURNED_SQLSTATE, errorMessage = MESSAGE_TEXT;
    END;

    -- Perform the update
    UPDATE `test_db2`.`users`
        SET name = NEW.name,
            age = NEW.age
        WHERE id = NEW.id;

    -- Check whether the update was successful
    IF errorCode != '00000' THEN
        INSERT INTO `errors` (code, message, query_type, record_id, on_db, on_table) VALUES (errorCode, errorMessage, 'update', NEW.id, 'test_db2', 'users');
    END IF;
END; //

-- TRIGGER FOR DELETE
DROP TRIGGER IF EXISTS `test_db1_users_ad`;
CREATE TRIGGER `test_db1_users_ad` AFTER DELETE ON `users` FOR EACH ROW 
BEGIN
    -- Declare variables to hold diagnostics area information
    DECLARE errorCode CHAR(5) DEFAULT '00000';
    DECLARE errorMessage TEXT DEFAULT '';

    -- Declare exception handler for failed insert
    DECLARE CONTINUE HANDLER FOR SQLEXCEPTION 
    BEGIN
      GET DIAGNOSTICS CONDITION 1
        errorCode = RETURNED_SQLSTATE, errorMessage = MESSAGE_TEXT;
    END;

    -- Perform the delete
    DELETE FROM `test_db2`.`users`
        WHERE id = OLD.id;

    -- Check whether the insert was successful
    IF errorCode != '00000' THEN
        INSERT INTO `errors` (code, message, query_type, record_id, on_db, on_table) VALUES (errorCode, errorMessage, 'delete', OLD.id, 'test_db2', 'users');
    END IF;
END; //

-- DELIMITER;

Hope this will help others when they come over here.

Cheers,

Comments