How to reconnect MySQL connection in Node.js program?

How to reconnect MySQL connection in Node.js program?

MySQL is a popular relational database, and Node.js is a very popular server-side programming language. It's common to use the two together. Connecting to a MySQL database in a Node.js program allows us to manipulate, store and retrieve data. However, sometimes the MySQL connection may be disconnected due to various reasons. At this time, we need to implement a reconnection mechanism in the program to ensure the stability and reliability of the program. This article will introduce how to implement MySQL connection reconnection in Node.js program.

1. Install the MySQL module

Before we start, we need to install the MySQL module in the Node.js project. You can use the npm command to install:

npm install mysql

2. Create a MySQL connection

In the Node.js program, we need to use the MySQL module to create a connection to the database. You can use the following code to create a MySQL connection:

const mysql = require('mysql');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: 'password',
  database: 'mydatabase'
});

connection.connect(function(err) {
  if (err) {
    console.error('Error connecting to MySQL database: ' + err.stack);
    return;
  }

  console.log('Connected to MySQL database as ID: ' + connection.threadId);
});

In the above code, we pass the connection configuration object, which contains database-related information, such as host address, user name, password, and database name. By calling the connect method, we can create a connection to the database. If the connection fails, an error message will be printed; if the connection is successful, the connection's thread ID will be printed.

3. Listening to MySQL connection errors

In order to implement the reconnection mechanism, we need to monitor MySQL connection errors. When a connection error occurs, we will perform a reconnection operation. Connection errors can be monitored through the following code:

connection.on('error', function(err) {
  console.error('MySQL connection error: ' + err.stack);

  // 重连
  connection.connect(function(err) {
    if (err) {
      console.error('Error reconnecting to MySQL database: ' + err.stack);
      return;
    }

    console.log('Reconnected to MySQL database as ID: ' + connection.threadId);
  });
});

In the above code, we use the connection.on method to bind the error event. When a connection error occurs, The callback function will be executed. In the callback function, we can output the stack of error information, and then call the connect method again to try to reconnect to the database.

4. Writing a reconnection strategy

In actual applications, simply performing unlimited reconnections may lead to too many connection attempts, causing adverse effects on the database and server. necessary burden. Therefore, we need to implement a reasonable reconnection strategy. The following code exemplifies a simple reconnection strategy, which reconnects every once in a while until the connection is successful:

function reconnect() {
  // 尝试重新连接
  connection.connect(function(err) {
    if (err) {
      console.error('Error reconnecting to MySQL database: ' + err.stack);
      setTimeout(reconnect, 2000); // 2秒后再次尝试重连
      return;
    }

    console.log('Reconnected to MySQL database as ID: ' + connection.threadId);
  });
}

// 失败后尝试连接
connection.on('error', function(err) {
  console.error('MySQL connection error: ' + err.stack);
  reconnect();
});

In the above code, we define a method named reconnect The function performs the reconnection operation in the function. If the connection fails, an error message will be printed and the connection will be tried again after 2 seconds. At the same time, we also bind the error event to the reconnect function to reconnect when an error occurs in the connection.

5. Start the connection

After everything is ready, we only need to start the MySQL connection at the right time. This usually happens at program startup or where there is a need to access a database. The connection can be initiated through the following code:

connection.connect(function(err) {
  if (err) {
    console.error('Error connecting to MySQL database: ' + err.stack);
    return;
  }

  console.log('Connected to MySQL database as ID: ' + connection.threadId);
});

In the above code, we simply called the connect method to establish the connection. If the connection fails, an error message will be printed; if the connection is successful, the connection's thread ID will be printed.

Summary:

Reconnection is a very important mechanism to ensure a stable and reliable connection between the Node.js program and the MySQL database. By listening for connection errors and implementing a reasonable reconnection strategy, we can ensure that when the connection is disconnected, it can be reconnected in time to avoid program crashes or data loss. I hope this article can help you implement MySQL connection reconnection in Node.js programs.

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