How to write triggers in MySQL using JavaScript

How to write triggers using JavaScript in MySQL

MySQL is a powerful relational database management system that provides many functions and tools to handle database operations. In MySQL, we can use JavaScript to write triggers to implement automated operations. This article will introduce how to use JavaScript to write triggers in MySQL and provide some specific code examples.

1. Preparation
   First, we need to ensure that the MySQL version is 5.7 or higher and the MySQL Shell has been installed. MySQL Shell is an interactive command line tool that supports the use of JavaScript to write and execute MySQL scripts. You can download and install MySQL Shell from the MySQL official website.
2. Create a database
   Before we start writing triggers, we first need to create a database. In MySQL Shell, use the following command to create a new database:

CREATE DATABASE mydb;

3. Create a table
   Next, we need to create a table Create a new table in the created database. Tables will be used to store data and trigger trigger actions. Create a new table in MySQL Shell using the following command:

USE mydb;
CREATE TABLE users (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50),
age INT
);

4. Writing Triggers
   Once the database and tables are ready, we can start writing JavaScript triggers. In the MySQL Shell, create a new file and copy the following code into the file:

//Introduce the modules you need to use
var mysqlx = require('mysqlx');

//Connect to the database
var session = mysqlx.getSession({
user: 'root',
password: 'password',
host: 'localhost',
port: 33060
});

// Create trigger
session.sql("CREATE TRIGGER after_insert_users AFTER INSERT ON users FOR EACH ROW BEGIN
DECLARE msg VARCHAR(255) ;
SET msg = CONCAT('A new user has been inserted. User ID: ', NEW.id);
INSERT INTO log (message) VALUES (msg);
END;")
.execute();

// Close the session
session.close();

Please note that the trigger in the above code is named "after_insert_users", and in each Executed every time a new row is inserted. In this example, the trigger will insert a record into another table named "log", recording the information of the newly inserted user.

5. Execute trigger
   Once the trigger has been written, we can use MySQL Shell to execute the trigger. In MySQL Shell, use the following command to load and execute the file we wrote earlier:

source /path/to/trigger.js

Please change "/path/to/trigger .js" with the actual path where you saved the trigger file.

6. Testing the Trigger
   Now we can test that the trigger works as expected. Try to insert a new record into the "users" table and check whether the "log" table has a corresponding record. An example is as follows:

INSERT INTO users (name, age) VALUES ('John Doe', 25);

SELECT * FROM log;

If everything is OK , you should be able to see a record in the "log" table containing the newly inserted user information.

Summary
In this article, we learned how to write triggers in MySQL using JavaScript. We first prepared the MySQL environment, and then created a database and a table. Next, we wrote a trigger to automate the action. Finally, we executed the trigger and tested that it worked as expected.

Please keep in mind that this is just a very simple example, you can write more complex triggers based on your needs and business logic. I hope this article helps you understand how to write triggers in MySQL using JavaScript!

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