Backend Notes

These notes are created from the youtube channel Sheriyans Coding School and from the following videos:

• 🚀 Backend - The EndGame (Part-1)
• 🚀 Backend - The EndGame (Part-2)

Topic 1: Express Generator

• It is used to automatically create all the files and folder structure for the express js project.

• To use express-generator, run the following commands in the terminal:

  • To globally install express-generator in the system

    npm i express-generator -g

  • To create a project with express generator

    express appname --view=ejs

  • To go to the project directory

    cd appname

  • To install the node modules in the project

    npm install

  • Run only if nodemon is not installed

    npm i nodemon

  • To run the server

    npx nodemon

  • NOTE: Do not provide filename while using express-generator. Example, npx nodemon script.js

• The changes that occurred because of using express-generator are:

  • app.get is converted to router.get in index.js and user.js
  • npx nodemon script.js is converted to npx nodemon

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Topic 2: Mongo db

• It is used to create database for a project.

• The following are the things you should keep in mind while understanding mongo db.

  Code side	MongoDB side
  1. DB Setup	DB Formation
  2. Model	Collection
  3. Schema	Documents

• Lets understand these terms:

  • DB Setup: Creation of database
  • Model: It is the code written to create a collection.
  • Collection: A collection is a specific section of the database wherea a particular data is stored. Example, user collection - here all the data of different users will be stored.
  • Schema: It is the code written to define the structure of a document. It specifies the information to be stored in the collection and its data type.
  • Document: A document is the single entity of the collection. Example, information about a single user present in the users collection.

Steps to setup Mongo db:

• Install community edition of mongo db. It requires internet connection for installation.

• Instal mongoose js by writing command in the terminal:

   npm i mongoose

• Follow the steps and write the code in the users.js file to setup connection.

  • Step 1: Require mongoose

    const mongoose = require('mongoose');

  • Step 2: Create Database

    mongoose.connect("mongodb://127.0.0.1:27017/database_name")

    here,

    • connect() is a function of mongoose. It is used to establish a connection to a MongoDB database.
    • mongodb://: indicates the protocol used to connect to MongoDB.
    • 127.0.0.1: is the IP address (localhost) where the MongoDB server is running.
    • 27017: is the default port number for MongoDB. MongoDB listens for client connections on this port by default.
    • database_name: is the name of the specific database to which you want to connect.

  • Step 3: Create Schema

    const schemaName = mongoose.Schema({
     //   ( information : Data type ) => Format
        username : String,
        name : String,
        age : Number
    })

  • Step 4: Create model and export

    module.exports = mongoose.model( "collectionName", schemaName )

• After performing all the steps, the users.js file will look like.

  const mongoose = require("mongoose");
  
  mongoose.connect("mongodb://127.0.0.1:27017/database_name");
  
  const schemaName = mongoose.Schema({
      username : String,
      name : String,
      age : Number
  })
  
  module.exports = mongoose.model( "collectionName" , schemaName )

Steps to use Mongo db:

• Import express package and userModel from users.js to index.js.

  var express = require('express');
  var router = express.Router();
  
  const userModel = require("./users");

• To create a user in a collection, write the following code below the above code:

  router.get("/create" , async function(req, res){
      const createdUser = await userModel.create({
          username : "Username",
          name : "Your Name",
          age : 10
      });
      res.send(createdUser);
  })

• To find all users in a collection, write the following code below the above code:

  router.get("/allusers", async function(req, res){
      const allusers = await userModel.find();
      res.send(allusers);
  })

• To find single user in a collection, write the following code below the above code:

  router.get("/user", async function(req, res){
      const user = await userModel.findOne({username : "Username"});
      res.send(user);
  })

• To delete single user in a collection, write the following code below the above code:

  router.get("/delete", async function(req, res){
      const deletedUser = await userModel.findOneAndDelete({username : "Username"});
      res.send(deletedUser);
  })

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Topic 3: Session

• Session is used to store the data on the server.

• It can be stored as key-value pairs where keys are unique identifiers and values are the corresponding data.

• It can be stored for a specific duration or until the browser session ends.

• Express provides middleware called session which allows us to use sessions in our application.

• Steps To implement Sessions in your app are as follows :

  • Install the required package.

    npm install express-session

  • Require express-session in app.js by using

    var session = require("express-session")

  • Configure session in middleware using

    app.use(session({
        resave : false,
        saveUninitialized: false,
        secret : "holabolaholabola"
    }));

    here,

    • resave: This option controls whether the session should be saved back to the session store if it was not modified during the request. Setting it to false helps to prevent unnecessary session saves.
    • saveUninitialized: This option controls whether a session should be stored if it is unmodified (not initialized).
    • secret: This is the secret used to sign the session ID cookie.

• Steps to create a session. Write the below code in index.js

  • To create a session, write the code in the following way:

    router.get("/", function(req,res){
        req.session.ban = true;
        res.render("index");
    })

  • To check a session, write the code in the following way:

    router.get("/checkban", function (req, res) {
        if (req.session.ban === true) res.send("User Banned");
        else res.send("User is not banned");
    });

  • To destroy a session, write the code in the following way:

    router.get("/remove", function (req, res) {
        req.session.destroy(function (err) {
            if (err) throw Error();
            res.send("Ban removed");
        });
    });

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Topic 4: Cookies

• Cookie is used to store the data on the browser.

• They are very useful when you want to keep some information about the user even after he closes the browser.

• To create cookie, you have to install cookie-parser package. This package is automatically installed by the express-generator.

• Also this package is initialized by the express-generator using app.use(cookieParser());.

• Steps to create Cookie. Write the below code in index.js

  • To create a cookie, write the code in the following way:

    router.get('/', function(req, res){
        res.cookie("age" , 25)
        res.send("Created")
    });

  • To check a cookie, write the code in the following way:

    router.get('/find', function(req, res){
        console.log(req.cookies);
        res.send("found")
    });

  • To clear a cookie, write the code in the following way:

    router.get('/clear', function(req, res){
        res.clearCookie("age");
        res.send("Cleared")
        });

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Congratulations.... 🥳🎉🎊

You have succesfully learnt express-generator, Mongo DB, Session and Cookies