CODEWITHSUNDEEP
javascriptnode.jsdb2
peterremec
peterremec

Reputation: 516

Node js database connection in a separate module

I made node.js app that includes some REST services. Those services connect to a database (for example Oracle or DB2) to execute some query.

Since I'm a beginner in node.js programming, I have a question about my case: What's the right way to access to a database? Is it better to have one connection reference while the app is running and use the same connection instance when REST services are called?

I found some examples that includes database connection in a separate module and use that module in app, something like that:

db2.js:

var db2 = require('ibm_db');

var db2ConnSettings = "DRIVER={DB2};DATABASE=mydb;HOSTNAME=localhost;UID=db2test;PWD=db2test;PORT=50000;PROTOCOL=TCPIP";

var db2Conn = db2.open(db2ConnSettings, function(err, conn) {
        if (err)
            return console.log(err);
    });

module.exports = db2Conn;

server.js:

var express = require('express');
var app = express();
var db2Connection = require('./db2.js');

app.get('/data', function(req, res) {
    console.log(db2Connection );
    // make some query
});

When this service is called, db2connection is undefined. How come? How should I retrieve a db2 connection from db2.js file?

Upvotes: 0

Views: 2555

Answers (2)

Christopher Jones
Christopher Jones

Reputation: 10496

For Oracle with node-oracledb it's simple to create and use a connection pool. Your app would just get a free connection from the pool whenever it handles an HTTP REST request. Look at webapp.js and webapppromises.js in the examples. Node-oracledb has a 'connection pool queue' (see doc) which handles connection load spikes. It also has a 'connection pool cache' (also see the doc) which makes it easy to access a pool created in a different module.

Upvotes: 2

Whothehellisthat
Whothehellisthat

Reputation: 2152

As said by @Sirko:

db2.js

var db2 = require('ibm_db');
var db2ConnSettings = "DRIVER={DB2};DATABASE=mydb;HOSTNAME=localhost;UID=db2test;PWD=db2test;PORT=50000;PROTOCOL=TCPIP";

var err, conn;
var callbacks = [];

module.exports = function(callback) {
  // db2 module is called

  if (err || conn) {
    // connection has already been established
    //   (results of db2.open have been stored)
    // callback immediately
    callback(err, conn);
  }
  else {
    // connection has not been established
    // store the callback for when db connects
    callbacks.push(callback);
  }
};

db2.open(db2ConnSettings, function(_err, _conn){
  // db has connected

  err = _err; conn = _conn; // store results
  var next_callback;

  // array.pop() removed the last item from the array
  // and returns it. if no items are left, returns null.
  // so this loops through all stored callbacks.
  while(next_callback = callbacks.pop()) {
    // the removed item is stored in next_callback
    next_callback(err, conn); // send connection results to callback
  }

  // no more items in callbacks to trigger
});

server.js

var express = require('express');
var app = express();
var db2Connection = require('./db2.js')(function(err, conn) {
  // triggered if the connection has already been established
  // or as soon as it HAS been established
  app.get('/data', function(req, res) {
      console.log(conn);
      // ...
  });
});

Upvotes: 2

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