Nodejs 连接 mysql时报Error: Cannot enqueue Query after fatal error错误的处理办法

首先，需要理解该错误的产生原因，即在于连接的mysql实例出现了致命错误，后续再进行查询等操作就会出现该错误。

处理该错误的方式如下：

1. 在创建连接的时候，加上supportBigNumbers: true, 与 bigNumberStrings: true配置。

const mysql = require('mysql');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'user',
  password: 'password',
  database: 'database',
  supportBigNumbers: true,
  bigNumberStrings: true
});

connection.connect((err) => {
  if (err) {
    console.error('error connecting: ' + err.stack);
    return;
  }

  console.log('connected as id ' + connection.threadId);
});

1. 在进行mysql操作之前，需要验证连接状态，如果连接不正常，需要进行重连。

const mysql = require('mysql');

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

  connection.connect((err) => {
    if (err) {
      console.error('error connecting: ' + err.stack);
      setTimeout(handleDisconnect, 2000);
      return;
    }

    console.log('connected as id ' + connection.threadId);
  });

  connection.on('error', (err) => {
    if (err.code === 'PROTOCOL_CONNECTION_LOST') {
      console.error('Database connection was closed.');
      handleDisconnect();
    } else {
      throw err;
    }
  });
}

handleDisconnect();

示例1：使用第一种方式处理同步查询mysql出现该错误的情况。

const mysql = require('mysql');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'user',
  password: 'password',
  database: 'database',
  supportBigNumbers: true,
  bigNumberStrings: true
});

connection.connect((err) => {
  if (err) {
    console.error('error connecting: ' + err.stack);
    return;
  }

  console.log('connected as id ' + connection.threadId);

  connection.query('SELECT * FROM users', (error, results, fields) => {
    if (error) {
      console.log('Error occurred:', error);
      return;
    }

    console.log('Results:', results);
  });
});

示例2：使用第二种方式处理同步查询mysql出现该错误的情况。

const mysql = require('mysql');

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

  connection.connect((err) => {
    if (err) {
      console.error('error connecting: ' + err.stack);
      setTimeout(handleDisconnect, 2000);
      return;
    }

    console.log('connected as id ' + connection.threadId);

    connection.query('SELECT * FROM users', (error, results, fields) => {
      if (error) {
        console.log('Error occurred:', error);
        return;
      }

      console.log('Results:', results);
      connection.end();
    });
  });

  connection.on('error', (err) => {
    if (err.code === 'PROTOCOL_CONNECTION_LOST') {
      console.error('Database connection was closed.');
      handleDisconnect();
    } else {
      throw err;
    }
  });
}

handleDisconnect();

通过以上两种方式，可以避免出现Nodejs连接mysql时报Error: Cannot enqueue Query after fatal error错误，并保证mysql连接正常进行数据操作。