RESTful APIs using NodeJS, ExpressJS, and MS SQL Server

REST (REpresentational State Transfer) is an architectural style for developing web services that uses HTTP. REST server provides access to resource and REST client modifies the resources. REST is popular due to its simplicity. REST uses different representation methods to represent resources like JSON, XML and text but most popular one is JSON.

Advantages of Restful services

Language independent architectural style
simple
reliable
scalable
implementation is easy

NodeJS is a very popular and powerful JavaScript framework. we can develop attractive web applications like video streaming sites, single page web applications, etc. And Node is open source.

Advantages of NodeJS

Easy implementation
Lightweight, fast and scalable
streaming capability
high performance
real-time web applications
Community friendly

ExpressJS is also written in JavaScript and it is also open source. We can use ExpressJS for build web applications and APIs. It has been called the de facto standard server framework for Node.js.

Advantages of ExpressJS

Has the biggest Community
Most matured framework
simple
code re usability
easy implementation
allows you o define error handling middle-ware.

Let's start to implement a RESTful Web Service,

Step 1 :- Create a package.json file. That file contains the initial configuration and we can use following commands to create that.

npm init or npm init -y

Step 2 :- Create server.js file. That contains server configurations and initialization of database connection and also it contains APIs as your requirement.

Example:-

//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);
});

Step 3 :- I recommend the Visual studio code to do the implementation. If not you can run those commands using CMD and if using VS Code you can run commands using VS Code terminal. Run npm install command to that installs all the necessary node modules. After that run node server.js command and it will starts the server on localhost:8080.

Step 4 :- We can test our APIs using API testing tool like katalon studio, postman, apigee, etc. I recommend postman to do the API testings. It is open source and easy to use.

Following video will give you brief idea about node APIs using ExpressJs,