Nodejs Multiple pools created on refresh - node.js

Question

I have several DBs for which i am using connection pools in node.js. Every time i refresh page i think pools are created again. i refresh page 3 times and 3 times promises resolved. i have removed several databases just to make it little bit easier to read here.
and if i un-comment connection close line my app crashes. i can't seem to figure out why
const config = require("../config/config");
const oracledb = require("oracledb");
var crm1connPromise = new Promise((resolve, reject) => {
oracledb.createPool({
user: config.crm1.user,
password: config.crm1.password,
connectString: config.crm1.connectString,
poolAlias: config.crm1.poolAlias,
poolMin: 0,
poolMax: 10,
poolTimeout: 300
}, (error, pool) => {
if (error) {
reject(err);
}
resolve("CRM1 Promise resolved")
});
});
var query2connPromise = new Promise((resolve, reject) => {
oracledb.createPool({
user: config.query2.user,
password: config.query2.password,
connectString: config.query2.connectString,
poolAlias: config.query2.poolAlias,
poolMin: 0,
poolMax: 10,
poolTimeout: 300
}, (error, pool) => {
if (error) {
reject(err);
}
resolve("QUERY2 Promise resolved --------")
});
});
var promiseArray = [crm1connPromise, crm2connPromise, crm3connPromise, crm4connPromise, csfp1connPromise, csfp2connPromise, csfp3connPromise, csfp4connPromise, cact1connPromise, cact2connPromise, cact3connPromise, cact4connPromise, cospconnPromise, cchnconnPromise, bbaseconnPromise, bcdrconnPromise, vcdbconnPromise, crptconnPromise, query2connPromise];
function getDBConnection (dbname) {
return new Promise((resolve, reject) => {
try {
Promise.all(promiseArray).then((message) => {
console.log(message);
const pool = oracledb.getPool(dbname);
pool.getConnection( (err, connection) => {
if (err) {
reject(err);
console.log(err);
}
resolve(connection);
});
});
} catch (error) {
reject(error);
}
});
}
module.exports.query = function(dbname, sql, bind = []){
return new Promise ((resolve,reject) =>{
var conn
try {
getDBConnection(dbname).then((connection) =>{
connection.execute(sql,bind,(err,result)=>{
if (err){
reject(err);
}
resolve(result);
})
//connection.close(0);
})
} catch (error) {
reject(error);
}
})
}

Answer 1

you can use 'Singleton'
please google 'Singleton pattern' and examples.
like this:
dataBaseManager.js:
'use strict'
var Singleton = (function () {
var instance;
function createInstance() {
var object = new dataBaseManager();
return object;
}
return {
getInstance: function () {
if (!instance) {
instance = createInstance();
}
return instance;
}
};
})();
function dataBaseManager() {
this.connected = false;
this.client = null;
this.dataBase = null;
//public methods
this.connect = function () {
try {
your_database.connect({}, (err, client) => {
if (err) {
this.connected = false;
this.client = null;
this.dataBase = null;
return;
}
this.connected = true;
this.client = client;
this.dataBase = client.db();
});
} catch (error) {
}
};
this.disconnect = function () {
try {
if (this.client) {
this.client.close();
this.connected = false;
this.client = null;
this.dataBase = null;
}
} catch (error) {
}
}
}
module.exports = Singleton;
repository.js:
const dataBaseManager = require("./dataBaseManager").getInstance();
your_get_dample_data_from_data_base_func = function (data) {
dataBaseManager.dataBase
.find({})
.toArray(function (err, result) {
if (err) {
return callback(err, null);
}
callback(null, result);
});
};
index.js:
const dataBaseManager = require("./dataBaseManager").getInstance();
function connect() {
dataBaseManager.connect();
}
function disconnect() {
dataBaseManager.disconnect();
}

Answer 2

Look at the node-oracledb example webappawait.js which starts the pool outside the web listener code path.
async function init() {
try {
await oracledb.createPool({
user: dbConfig.user,
password: dbConfig.password,
connectString: dbConfig.connectString
});
const server = http.createServer();
server.on('error', (err) => {
console.log('HTTP server problem: ' + err);
});
server.on('request', (request, response) => {
handleRequest(request, response);
});
await server.listen(httpPort);
console.log("Server is running at http://localhost:" + httpPort);
} catch (err) {
console.error("init() error: " + err.message);
}
}
async function handleRequest(request, response) {
. . .
}