How to switch from using mysql.createConnection to mysql.createPool - mysql

Question

I'm fairly new to how database connections work using nodejs, and I'm having issues with database connections that aren't being closed properly. I've asked a few questions on here before about it, and it seems like everyone is telling me to use pool instead of the way I have been doing it. The only problem is that when I search online about using pool from promise-mysql, everyone seems to use a very simple and generic approach, but I'm using it within a complex application using sockets. So I'm wondering how I can switch my old approach using createConnection() to using pool instead, in hopes of clearing up these connection issues.
Each time I call a socket it makes a connection to the database and then releases it after it is complete, or so it seems. It sounds like this is not a very scalable approach, and that using pool will help run multiple queries in parallel.
db.js:
import mysql from 'promise-mysql';
import env from '../../../env.config.json';
const db = async (sql, descriptor, serializedParameters = []) => {
return new Promise( async (resolve, reject) => {
try {
const connection = await mysql.createConnection({
host: env.DB.HOST,
user: env.DB.USER,
password: env.DB.PASSWORD,
database: env.DB.NAME,
port: env.DB.PORT
})
if (connection && env.ENV === "development") {
//console.log(/*"There is a connection to the db for: ", descriptor*/);
}
let result;
if(serializedParameters.length > 0) {
result = await connection.query(sql, serializedParameters)
} else result = await connection.query(sql);
connection.end();
resolve(result);
} catch (e) {
console.log("ERROR pool.db: " + e);
reject(e);
};
});
}
export default db;
This is an example of how I would create a connection to query the db
inventory.js:
import db from '../API/db';
export const selectAllFromBuildItems = () => {
return new Promise( async (resolve, reject) => {
try {
const getAllBuildItems = "SELECT * FROM mydb.build_items;"
const response = await db(getAllBuildItems, "AllBuildItems");
resolve(response);
} catch (e) {
console.log("ERROR inventory.selectAllFromBuildItems: " + e);
reject(e);
}
});
};
How can I change my code so that I use a pool instead. I have a lot of different queries that can be called from our application so I'm not quite sure what the right approach for this would be. I saw some people say that I should create the pool once and then use it throughout the application, but I don't know where that would go. If anyone has any suggestions on how I can make this switch, that would help me out a lot. Thanks!

Answer 1

Create the pool. Better if you create once when you run your application.
If it is in different file then you have export here and import in required file.
var pool = mysql.createPool({
host: env.DB.HOST,
user: env.DB.USER,
password: env.DB.PASSWORD,
database: env.DB.NAME,
connectionLimit: 10
});
I had to create this prototype function as the library had a bug of close connection was not returning the connection to the pool.
pool.prototype.releaseConnection = function releaseConnection(connection) {
return this.pool.releaseConnection(connection.connection);
};
Funtion for getting connection from the pool that is created earlier.
If you want you can call pool.getConnection() in all your query functions.
function connect() {
return pool.getConnection().then(function(connection) {
return connection
}).catch(function(e) {
console.log("Error Creating Connection");
throw e;
});
}
Now this is your query function to get data from dd.
function selectAllFromBuildItems() {
var sql_query = `SELECT * FROM mydb.build_items`;
return connect().then(function(conn) {
return conn.query(sql_query).then(function(rows) {
pool.releaseConnection(conn);
return rows;
});
}).catch(function(e) {
console.log("ERROR inventory.selectAllFromBuildItems: " + e);
throw e;
});
}
Update: Descriptions are added. Hope this helps you.