can't handle db connection error

[sashsvamir]

I'm using mysql-query-promise with koa. When mysql has failed to connect to db, nodejs has been exited.

Error: ER_DBACCESS_DENIED_ERROR: Access denied for user 'root'@'localhost' to database 'dbtest'
    at Handshake.Sequence._packetToError (...../koa/node_modules/mysql/lib/protocol/sequences/Sequence.js:52:14)
    at Handshake.ErrorPacket (...../koa/node_modules/mysql/lib/protocol/sequences/Handshake.js:130:18)
    at Protocol._parsePacket (...../koa/node_modules/mysql/lib/protocol/Protocol.js:279:23)
    at Parser.write (...../koa/node_modules/mysql/lib/protocol/Parser.js:76:12)
    at Protocol.write (...../koa/node_modules/mysql/lib/protocol/Protocol.js:39:16)
    at Socket.<anonymous> (...../koa/node_modules/mysql/lib/Connection.js:103:28)
    at Socket.emit (events.js:180:13)
    at addChunk (_stream_readable.js:274:12)
    at readableAddChunk (_stream_readable.js:261:11)
    at Socket.Readable.push (_stream_readable.js:218:10)
    --------------------
    at Protocol._enqueue (...../koa/node_modules/mysql/lib/protocol/Protocol.js:145:48)
    at Protocol.handshake (...../koa/node_modules/mysql/lib/protocol/Protocol.js:52:23)
    at PoolConnection.connect (...../koa/node_modules/mysql/lib/Connection.js:130:18)
    at Pool.getConnection (...../koa/node_modules/mysql/lib/Pool.js:48:16)
    at PoolCluster._getConnection (...../koa/node_modules/mysql/lib/PoolCluster.js:229:13)
    at PoolNamespace.getConnection (...../koa/node_modules/mysql/lib/PoolNamespace.js:40:11)
    at ...../koa/node_modules/mysql/lib/PoolNamespace.js:45:17
    at ...../koa/node_modules/mysql/lib/PoolCluster.js:232:7
    at Handshake.onConnect [as _callback] (...../koa/node_modules/mysql/lib/Pool.js:58:9)
    at Handshake.Sequence.end (...../koa/node_modules/mysql/lib/protocol/sequences/Sequence.js:88:24)
[nodemon] app crashed - waiting for file changes before starting...

I want to handle connection error, so i tried to handle error on koa middleware (see below), koa event handler and on mysql-query-promise promise catch handler (see below), but any of this both methods not executes on connection error and node has falled.

// koa middleware error handler
app.use((ctx, next) => {
  try {
    await next()
  } catch (err) {
    console.error(err)
  }
})

// koa event error handler
app.on('error', err => {
  console.log(err)
})

// mysql-query-promise error handler
const query = require('mysql-query-promise')
const q = query(`SELECT * from ${tableName}`, [String(token)])
await q
  .then((rows) => {
    // success
  }, (err) => {
    console.log('CATCH ERROR!')
  })

How can i handle mysql-query-promise connection error?

[ApelSYN]

node-mysql-query-promise works together with the config module.
To setup connection please create folder "config" in root of your project and put file "default.js" to config folder.
Example of default.js:

module.exports = {
    database: {
        'master': {
            host: 'localhost',
            user: 'username',
            password: 'password',
            port: '3306',
            database: 'database',
            connectionLimit: 10
        },
        'slave': {
            host: 'localhost',
            user: 'username',
            password: 'password',
            port: '3306',
            database: 'database',
            connectionLimit: 10
        }
    }
};

Edit this file for your settings.

Вот пример использования:

    var query = require('mysql-query-promise'),
        qs = 'SELECT * FROM foo WHERE bar=?';
        
    query(qs, ['baz'], 'master')
        .then(function(rows){
            /* Do what you need with query results here */
        }, function(err){
            /* Errors handler */
        });

Note that the function has 3 arguments:
The query, the list of escaped fields, and the third argument of the section name in the configuration file.

Edit your example:

// ...
const q = query(`SELECT * from ${tableName}`, [], 'master')
// ...

or

// ...
const q = query(`SELECT * from ?`, [tableName], 'master')
// ...

[sashsvamir]

I know how to configure mysql-query-promise, this issue was opened because now on failed db connection nodejs has falled. And i can't find way to catch this errors.

[ApelSYN]

Try:

try {
    let rows = await q
} catch (err) {
    console.log("Error!")
}

[sashsvamir]

no, error still not catching!

[ApelSYN]

Unfortunately I do not have the opportunity to quickly fix this problem, because the error occurs in the mysql-query module, which is written in the callback style. That's why koa can not catch this error.

We can fix this error in the following releases.