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How to config Sequelize ORM to execute serialized queries

I'm working on an electron app which executes write queries like - insert, delete, update etc. concurrently. I'm using SQLite which is single threat database, So if the app fires multiple write queries concurrently, the SQLite database is showing error that Database is locked. So How can I config the sequelize to execute serialized queries?
const { app } = require('electron')
const { Sequelize } = require('sequelize')
const path = require('path')
const cls = require('cls-hooked')
const namespace = cls.createNamespace('P&C.Beejak')
Sequelize.useCLS(namespace)
const db = new Sequelize({
dialect: 'sqlite',
storage: path.join(app.getPath('userData') + '/database', 'database.db'),
})
module.exports = db

Use transactions w/ the correct isolation method: https://sequelize.org/master/manual/transactions.html
// You can overwrite the isolationLevel setting globally with an option in the Sequelize constructor:
const { Sequelize, Transaction } = require('sequelize');
const sequelize = new Sequelize('sqlite::memory:', {
isolationLevel: Transaction.ISOLATION_LEVELS.SERIALIZABLE
});

TypeError: Cannot read property 'execute' of undefined . node.js how to export oracle db connection

Hi I am new to node and oracle.I have created a app and made a successfull connection to db.
I need to use connection object across the application how can i do that?
Below is my index.js file
const express = require("express");
const app = express();
const authRoute = require("./routes/auth");
app.use(express.json());
app.use("/api",authRoute) ;
app.listen(3000,function(){
console.log("Node Server : Running on port 3000...");
})
database connection file => connect.js
const oracledb = require('oracledb');
const dotenv = require('dotenv');
dotenv.config();
const connection = oracledb.getConnection(
{
user : process.env.USER,
password : process.env.PASS,
connectString : process.env.ConnectString
},
function(err, connection)
{
if (err) {
console.error(err.message);
return;
}
console.log('Connection was successful!');
connection.close(function(err){
if (err) {
console.error(err.message);
return;
}
});
});
module.exports = connection;
I want to use this db connection in my auth.js file
const router = require('express').Router();
const db = require('../database/connect');
router.post("/authenticate",function(req,res){
//console.log(req);
const user = req.body.username;
const username = {"name" : user};
const pass = req.body.key;
const password = {"pass" : pass};
//const result = db.execute('select * from usertable');// this doesn't work
//console.log(result.rows);
res.send('success');
});
module.exports = router;
when i run const result = db.execute('select * from usertable'); I get the error below.
TypeError: Cannot read property 'execute' of undefined
What am i doing wrong.Can anyone please help.Thanks in advance

I had faced this problem. You must install Oracle install client v 19 in your machine. You have to go to web install oracle instant client base on your machine.

(Update: there is a multi-part series with code showing what you want at https://github.com/oracle/oracle-db-examples/tree/main/javascript/rest-api)
Use a connection pool that is opened at app start. Then the pool cache can be used to get the pool (and then connections) in other modules.
For a web app like yours you definitely want to use a connection pool for performance.
There's a big section on connection pooling in the documentation. E.g see Connection Pool Cache which says:
When pools are created, they can be given a named alias. The alias can
later be used to retrieve the related pool object for use. This
facilitates sharing pools across modules and simplifies getting
connections.
The examples are worth reviewing.

How to reuse mongo client using globals, best practices

So, I have read other topics here in StackOverflow that try to touch on this but don't have a clear solution to the problem.
First I created a config file for the mongo client which is exported from it.
const { MongoClient } = require('mongodb');
const authMechanism = 'SCRAM-SHA-1';
const user = encodeURIComponent(process.env.MONGODB_USER);
const password = encodeURIComponent(process.env.MONGODB_PASSWORD);
const uri = `mongodb://${user}:${password}#${process.env.MONGODB_URI}?authMechanism=${authMechanism}`;
const client = new MongoClient(uri, {
useUnifiedTopology: true,
useNewUrlParser: true,
loggerLevel: 'info',
});
module.exports = client;
From there I understand that you must have mongo client initialised once, and only once, before you listen to your application, hence I have created this index.js (entry point to the app) file that does that requiring the typical app.js where all the node config is.
const app = require('./app');
const db = require('../configs/db/db-config');
const port = process.env.PORT;
db.connect((err, client) => {
if (err) {
throw err;
}
const database = client.db('dbnamegoeshere');
app.listen(port, () => console.log(`Listening on port ${port}...`));
});
Now, in order for me to reuse that db anywhere I want to make queries or whatever, what is the best practice? How could I add it globally? would adding it globally affect the performance or be a bad practice?
I have seen other examples where people perform these two tasks using a class but yet again all in the same file, not with an export or a global.
One final question, where, and why should I close the db client connection.
Thank you.

I think adding the db connection object to the global object works perfectly. And if you are worried about performance, just reassign global vars to local ones.
//dbconnection.js
const debug = require('debug')('someapp:mongo');
const mongoClient = require('mongodb').MongoClient;
const mongoOptions = {};
const mongoUrl = process.env.MONGO_URL || "mongodb://localhost:27017/dbname";
function callback(err, r){
debug("callback: ", err, r);
};
module.exports = function () {
mongoClient.connect(mongoUrl, mongoOptions, (err, client) => {
if(err){
debug("MongoDB connection error: ", err);
throw err;
};
const db = global.db = client.db();
});
};
And just use it like so in your root application file, once added to the file the db connection should be globally available in other files in your project.
//server.js
require("./dbconnection")();
const userDB = global.db.collection("Users");
userDB.find({}).toArray((err, items)=>{});

Node JS mssql exporting database connection

I have hard time understanding why my code doesn't work. I am using node package mssql and want to have database pool connection initiation in separate file:
databaseConnection.js:
const sql = require("mssql/msnodesqlv8");
config = {
database: process.env.DB_NAME,
server: process.env.DB_SERVER,
driver: "msnodesqlv8",
options: {
trustedConnection: true
}
};
let pool = sql.connect(config);
module.exports = pool;
Then I have my express route file data.js
const express = require("express");
const router = express.Router();
const db = require("../configs/databaseConnection");
router.get("/dataList", async (req, res) => {
let allData = await db.request().query("select * from dataList");
console.log(allData);
res.render("dataList", { title: "Data list" });
});
module.exports = router;
However, when I start the server and go to the route I get error:
(node:13760) UnhandledPromiseRejectionWarning: TypeError: db.request is not a function
The thing is if I setup precisely as this example mssql documentation (where verything would be done in the route) it works. However, if database connection is in separate file it doesn't work.
I would appreciate any help understanding this
Regards,
Rokas

sql.connect returns a promise, so once we know that, we can either do a .then(result => ... or use await, for example:
If you want to store the db object at startup for later I'd suggest changing the line:
const db = require("../configs/databaseConnection");
to
let db = null;
require("../configs/databaseConnection").then(pool => {
db = pool;
});

Mongoose and multiple database in single node.js project

I'm doing a Node.js project that contains sub projects. One sub project will have one Mongodb database and Mongoose will be use for wrapping and querying db. But the problem is
Mongoose doesn't allow to use multiple databases in single mongoose instance as the models are build on one connection.
To use multiple mongoose instances, Node.js doesn't allow multiple module instances as it has caching system in require(). I know disable module caching in Node.js but I think it is not the good solution as it is only need for mongoose.
I've tried to use createConnection() and openSet() in mongoose, but it was not the solution.
I've tried to deep copy the mongoose instance (http://blog.imaginea.com/deep-copy-in-javascript/) to pass new mongoose instances to the sub project, but it throwing RangeError: Maximum call stack size exceeded.
I want to know is there anyways to use multiple database with mongoose or any workaround for this problem? Because I think mongoose is quite easy and fast. Or any other modules as recommendations?

According to the fine manual, createConnection() can be used to connect to multiple databases.
However, you need to create separate models for each connection/database:
var conn = mongoose.createConnection('mongodb://localhost/testA');
var conn2 = mongoose.createConnection('mongodb://localhost/testB');
// stored in 'testA' database
var ModelA = conn.model('Model', new mongoose.Schema({
title : { type : String, default : 'model in testA database' }
}));
// stored in 'testB' database
var ModelB = conn2.model('Model', new mongoose.Schema({
title : { type : String, default : 'model in testB database' }
}));
I'm pretty sure that you can share the schema between them, but you have to check to make sure.

Pretty late but this might help someone. The current answers assumes you are using the same file for your connections and models.
In real life, there is a high chance that you are splitting your models into different files. You can use something like this in your main file:
mongoose.connect('mongodb://localhost/default');
const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', () => {
console.log('connected');
});
which is just how it is described in the docs. And then in your model files, do something like the following:
import mongoose, { Schema } from 'mongoose';
const userInfoSchema = new Schema({
createdAt: {
type: Date,
required: true,
default: new Date(),
},
// ...other fields
});
const myDB = mongoose.connection.useDb('myDB');
const UserInfo = myDB.model('userInfo', userInfoSchema);
export default UserInfo;
Where myDB is your database name.

One thing you can do is, you might have subfolders for each projects. So, install mongoose in that subfolders and require() mongoose from own folders in each sub applications. Not from the project root or from global. So one sub project, one mongoose installation and one mongoose instance.
-app_root/
--foo_app/
---db_access.js
---foo_db_connect.js
---node_modules/
----mongoose/
--bar_app/
---db_access.js
---bar_db_connect.js
---node_modules/
----mongoose/
In foo_db_connect.js
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/foo_db');
module.exports = exports = mongoose;
In bar_db_connect.js
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/bar_db');
module.exports = exports = mongoose;
In db_access.js files
var mongoose = require("./foo_db_connect.js"); // bar_db_connect.js for bar app
Now, you can access multiple databases with mongoose.

As an alternative approach, Mongoose does export a constructor for a new instance on the default instance. So something like this is possible.
var Mongoose = require('mongoose').Mongoose;
var instance1 = new Mongoose();
instance1.connect('foo');
var instance2 = new Mongoose();
instance2.connect('bar');
This is very useful when working with separate data sources, and also when you want to have a separate database context for each user or request. You will need to be careful, as it is possible to create a LOT of connections when doing this. Make sure to call disconnect() when instances are not needed, and also to limit the pool size created by each instance.

Mongoose and multiple database in single node.js project
use useDb to solve this issue
example
//product databse
const myDB = mongoose.connection.useDb('product');
module.exports = myDB.model("Snack", snackSchema);
//user databse
const myDB = mongoose.connection.useDb('user');
module.exports = myDB.model("User", userSchema);

A bit optimized(for me atleast) solution. write this to a file db.js and require this to wherever required and call it with a function call and you are good to go.
const MongoClient = require('mongodb').MongoClient;
async function getConnections(url,db){
return new Promise((resolve,reject)=>{
MongoClient.connect(url, { useUnifiedTopology: true },function(err, client) {
if(err) { console.error(err)
resolve(false);
}
else{
resolve(client.db(db));
}
})
});
}
module.exports = async function(){
let dbs = [];
dbs['db1'] = await getConnections('mongodb://localhost:27017/','db1');
dbs['db2'] = await getConnections('mongodb://localhost:27017/','db2');
return dbs;
};

I have been using this method and it works great for me until now.
const mongoose = require('mongoose');
function makeNewConnection(uri) {
const db = mongoose.createConnection(uri, {
useNewUrlParser: true,
useUnifiedTopology: true
});
db.on('error', function (error) {
console.log(`MongoDB :: connection ${this.name} ${JSON.stringify(error)}`);
db.close().catch(() => console.log(`MongoDB :: failed to close connection ${this.name}`));
});
db.on('connected', function () {
mongoose.set('debug', function (col, method, query, doc) {
console.log(`MongoDB :: ${this.conn.name} ${col}.${method}(${JSON.stringify(query)},${JSON.stringify(doc)})`);
});
console.log(`MongoDB :: connected ${this.name}`);
});
db.on('disconnected', function () {
console.log(`MongoDB :: disconnected ${this.name}`);
});
return db;
}
// Use
const db1 = makeNewConnection(MONGO_URI_DB1);
const db2 = makeNewConnection(MONGO_URI_DB2);
module.exports = {
db1,
db2
}