Building RESTful APIs using Node JS, Express JS, and MS SQL Server

REST (Representational State Transfer) is web standards based architecture and uses HTTP Protocol. A REST Server simply provides access to resources and REST client accesses and modifies the resources using HTTP protocol. REST uses various representations to represent a resource like text, JSON, and XML but JSON is the most popular one.

Why do we need RESTful Web Services?

REST is an architecture style for designing networked applications. REST is a lightweight alternative to mechanisms like RPC (Remote Procedure Calls) and Web Services (SOAP, WSDL, et al.). The World Wide Web itself, based on HTTP, can be viewed as an REST-based architecture. The entire modern web browsers are REST client. RESTful applications use HTTP methods (GET, POST, PUT, and DELETE) to perform CRUD operations.

Advantages:

1. Simple
2. Easy to use/implement
3. Easy to build
4. Uniform interface
5. The REST API is always independent of the type of platform or languages
6. Visible, reliable, and scalable

Why opt Node JS for building RESTful APIS?

Node.js is a powerful JavaScript framework built on Google Chrome’s JavaScript V8 Engine. It is used to develop I/O intensive web applications like video streaming sites, single-page applications, etc. Node.js is open source and used by thousands of developers around the world.

Advantages:

1. Quick & easy development
2. High performance
3. Run on single thread to handle multiple concurrent requests
4. Easy to write API and interaction code
5. Streaming support
6. Monitoring possibilities
7. Authentication support
8. Lightweight, fast, and scalable

About Express JS:

Express is a flexible Node.js web application framework that provides a robust set of features to develop mobile and web applications. It facilitates the rapid development of Node based Web applications. Few core features of Express framework −

• Allows setting up of middleware to respond to HTTP Requests.
• Defines a routing table which is used to perform different actions based on HTTP Method and URL.

Allows to the dynamic rendering of HTML Pages based on passing arguments to templates.

Getting Started

Prerequisites:

1. Node JS
2. MS SQL Server Database

App Setup & Execution:

Step 1: Create a package.json file.

{
  "name": "<Application Name>",//e.g.  – node_app
  "version": "0.0.0",
  "description": "<Description about your application>",
  "main": "server.js",
    "dependencies": {
        "express": "^4.14.0",
        "body-parser": "^1.15.2",
         “mssql”:”^ 3.3.0”
    },
    "scripts": {
    "start": "node server.js"
  },
  "author": {
    "name": "<Your Name>",
    "email": "<Your Email>"
  }
}

Note:  The package.json file can be created by using npm init command (recommended way).

Step 2: Create server.js file.

//Initiallising node modules
var express = require("express");
var bodyParser = require("body-parser");
var sql = require("mssql");
var app = express(); 

// Body Parser Middleware
app.use(bodyParser.json()); 

//CORS Middleware
app.use(function (req, res, next) {
    //Enabling CORS 
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, contentType,Content-Type, Accept, Authorization");
    next();
});

//Setting up server
 var server = app.listen(process.env.PORT || 8080, function () {
    var port = server.address().port;
    console.log("App now running on port", port);
 });

//Initiallising connection string
var dbConfig = {
    user:  “<dbUserName>”,
    password: “<dbPassword>”,
    server: “<dbHost_URL>”,
    database:” <dbName>”
};

//Function to connect to database and execute query
var  executeQuery = function(res, query){             
     sql.connect(dbConfig, function (err) {
         if (err) {   
                     console.log("Error while connecting database :- " + err);
                     res.send(err);
                  }
                  else {
                         // create Request object
                         var request = new sql.Request();
                         // query to the database
                         request.query(query, function (err, res) {
                           if (err) {
                                      console.log("Error while querying database :- " + err);
                                      res.send(err);
                                     }
                                     else {
                                       res.send(res);
                                            }
                               });
                       }
      });           
}

//GET API
app.get("/api/user ", function(req , res){
                var query = "select * from [user]";
                executeQuery (res, query);
});

//POST API
 app.post("/api/user ", function(req , res){
                var query = "INSERT INTO [user] (Name,Email,Password) VALUES (req.body.Name,req.body.Email,req.body.Password”);
                executeQuery (res, query);
});

//PUT API
 app.put("/api/user/:id", function(req , res){
                var query = "UPDATE [user] SET Name= " + req.body.Name  +  " , Email=  " + req.body.Email + "  WHERE Id= " + req.params.id;
                executeQuery (res, query);
});

// DELETE API
 app.delete("/api/user /:id", function(req , res){
                var query = "DELETE FROM [user] WHERE Id=" + req.params.id;
                executeQuery (res, query);
});

Note: You can add multiple routes based on your requirement.

Step 3: Open CMD, execute npm install command.

Step 4:  After successful installation of node modules, run below command into CMD.

node server.js

The node server will start running into port number 8080 with corresponding API Routes; you can point to the below URL to test the application.

http://localhost:8080

Step 5: Testing REST APIs

We can use any of the REST Clients like Postman Chrome App or through any of the Programming languages like Java, C#, PHP, etc., to consume the APIs.

Here is the demonstration using Postman App

Note: The complete code reference can be downloaded from the below link,

https://github.com/avinashl3175/Vm_BlogContent/blob/master/Node_API_Demo.zip