Introduction

To get paid for goods and services provided, businesses need to send invoices to their customers informing them of the services that they will be charged for. Back then, people had paper invoices which they gave to the customers when they contacted them for their services. With the advent and advancement of technology, people are now able to send electronic invoices to their customers.

In this tutorial you will build an invoicing application using Vue and NodeJS. This application will perform functions such as creating, sending, editing, and deleting an invoice.

Requirements

To follow through the article adequately, you’ll need the following:

• Node installed on your machine
• Node Package Manager (NPM) installed on your machine

Run the following to verify that Node is installed on your machine:

node --version

Run the following to verify that NPM is installed on your machine:

npm --version

If you get version numbers as results then you’re ready to proceed.

Step 1 — Setting Up Server

Now that we have the requirements all set, the next thing to do is to create the backend server for the application. The backend server will maintain the database connection.

Start by creating a folder to house the new project:

mkdir invoicing-app

Initialize it as a Node project:

cd invoicing-app && npm init

For the server to function appropriately, there are some Node packages that need to be installed. You can install them by running this command:

npm install --save express body-parser connect-multiparty sqlite3 bluebird path umzug bcrypt

That command installs the following packages:

• bcrypt to hash user passwords
• express to power our web application
• sqlite3 to create and maintain the database
• path to resolve file paths within our application
• bluebird to use Promises when writing migrations
• umzug as a task runner to run our database migrations
• body-parser and connect-multiparty to handle incoming form requests

Create a server.js file that will house the application logic:

touch server.js

In the server.js file, import the necessary modules and create an express app:

    const express = require('express')
    const bodyParser = require('body-parser');
    const sqlite3 = require('sqlite3').verbose();
    const PORT = process.env.PORT || 3128;

    const app = express();
    app.use(bodyParser.urlencoded({extended: false}));
    app.use(bodyParser.json());

    [...]

Create a / route to test that the server works:

    [...]

    app.get('/', function(req,res){
        res.send("Welcome to Invoicing App");
    });

    app.listen(PORT, function(){
        console.log(`App running on localhost:${PORT}`);
    });

app.listen() tells the server the port to listen to for incoming routes. To start the server, run the following in your project directory:

node server

Your application will now begin to listen to incoming requests.

Step 2 — Creating and Connecting To Database Using SQLite

For an invoicing application, a database is needed to store the existing invoices. SQLite is going to be the database client of choice for this application.

Start by creating a database folder:

mkdir database

Next, move into the new directory and create a file for your database:

cd database && touch InvoicingApp.db

In the database directory, run the sqlite3 client:

invoicing-app/database/   sqlite3

Open the InvoicingApp.db database:

.open InvoicingApp.db

Now that the database has been selected, next thing is to create the needed tables.

This application will use three tables:

• Users - This will contain the user data (id, name, email, company_name, password)
• Invoices - Store data for an invoice (id, name, paid, user_id)
• Transactions - Singular transactions that come together to make an invoice (name, price, invoice_id)

Since the necessary tables have been identified, the next step is to run the queries to create the tables.

Migrations are used to keep track of changes in a database as the application grows. To do this, create a migrations folder in the database directory.

mkdir migrations

This will house all the migration files.

Now, create a 1.0.js file in the migrations folder. This naming convention is to keep track of the newest changes.

cd migrations && touch 1.0.js

In the 1.0.js file, you first import the node modules:

    "use strict";
    const Promise = require("bluebird");
    const sqlite3 = require("sqlite3");
    const path = require('path');

    [...]

Then, the idea now is to export an up function that will be executed when the migration file is run and a down function to reverse the changes to the database.

    [...]
    module.exports = {
      up: function() {
        return new Promise(function(resolve, reject) {
          /* Here we write our migration function */
          let db = new sqlite3.Database('./database/InvoicingApp.db');
          //   enabling foreign key constraints on sqlite db
          db.run(`PRAGMA foreign_keys = ON`);

          [...]

In the up function, connection is first made to the database. Then the foreign keys are enabled on the sqlite database. In SQLite, foreign keys are disabled by default to allow for backwards compatibility, so the foreign keys have to be enabled on every connection.

Next, specify the queries to create the tables:

          [...]
          db.serialize(function() {
            db.run(`CREATE TABLE users (
              id INTEGER PRIMARY KEY,
              name TEXT,
              email TEXT,
              company_name TEXT,
              password TEXT
            )`);

            db.run(`CREATE TABLE invoices (
              id INTEGER PRIMARY KEY,
              name TEXT,
              user_id INTEGER,
              paid NUMERIC,
              FOREIGN KEY(user_id) REFERENCES users(id)
            )`);

            db.run(`CREATE TABLE transactions (
              id INTEGER PRIMARY KEY,
              name TEXT,
              price INTEGER,
              invoice_id INTEGER,
              FOREIGN KEY(invoice_id) REFERENCES invoices(id)
            )`);
          });
          db.close();
        });
      },
      [...]

The serialize() function is used to specify that the queries will be ran sequentially and not simultaneously.

Afterwards, the queries to reverse the changes are also specified in the down() function:

      [...]

      down: function() {
        return new Promise(function(resolve, reject) {
          /* This runs if we decide to rollback. In that case we must revert the `up` function and bring our database to it's initial state */
          let db = new sqlite3.Database("./database/InvoicingApp.db");
          db.serialize(function() {
            db.run(`DROP TABLE transactions`);
            db.run(`DROP TABLE invoices`);
            db.run(`DROP TABLE users`);
          });
          db.close();
        });
      }
    };

Once the migration files have been created, the next step is running them to make the changes in the database. To do this, create a scripts folder from the root of your application:

mkdir scripts

Then create a file called migrate.js:

cd scripts && touch migrate.js

Add the following to the migrate.js file:

    const path = require("path");
    const Umzug = require("umzug");

    let umzug = new Umzug({
      logging: function() {
        console.log.apply(null, arguments);
      },
      migrations: {
        path: "./database/migrations",
        pattern: /\.js$/
      },
      upName: "up",
      downName: "down"
    });

    [...]

First, the needed node modules are imported. Then a new umzug object is created with the configurations. The path and pattern of the migrations scripts are also specified. To learn more about the configurations, head over to the umzug GitHub page.

To also give some verbose feedback, create a function to log events as shown below and then finally execute the up function to run the database queries specified in the migrations folder:

    [...]

    function logUmzugEvent(eventName) {
      return function(name, migration) {
        console.log(`${name} ${eventName}`);
      };
    }

    // using event listeners to log events
    umzug.on("migrating", logUmzugEvent("migrating"));
    umzug.on("migrated", logUmzugEvent("migrated"));
    umzug.on("reverting", logUmzugEvent("reverting"));
    umzug.on("reverted", logUmzugEvent("reverted"));

    // this will run your migrations
    umzug.up().then(console.log("all migrations done"));

Now, to execute the script, go to your terminal and in the root directory of your application, run:

~/invoicing-app node scripts/migrate.js up

You will see output similar to the following:

Output
    all migrations done
    == 1.0: migrating =======
    1.0 migrating

Step 3 — Creating Application Routes

Now that the database is adequately set up, the next thing is to go back to the server.js file and create the application routes. For this application, the following routes will be made available:

URL	METHOD	FUNCTION
/register	POST	To register a new user
/login	POST	To log in an existing user
/invoice	POST	To create a new invoice
/invoice/user/{user_id}	GET	To fetch all the invoices for a user
/invoice/user/{user_id}/{invoice_id}	GET	To fetch a certain invoice
/invoice/send	POST	To send invoice to client

To register a new user, a post request will be made to the /register route of your server. This route will look like this:

    [...]
    const bcrypt = require('bcrypt')
    const saltRounds = 10;
    [...]

    app.post('/register', function(req, res){
        // check to make sure none of the fields are empty
        if( isEmpty(req.body.name)  || isEmpty(req.body.email) || isEmpty(req.body.company_name) || isEmpty(req.body.password) ){
            return res.json({
                'status' : false,
                'message' : 'All fields are required'
            });
        }
        // any other intendend checks

        [...]

A check is made to see if any of the fields are empty and if the data sent matches all the specifications. If an error occurs, an error message is sent to the user as a response. If not, the password is hashed and the data is then stored in the database and a response is sent to the user informing them that they are registered.

        bcrypt.hash(req.body.password, saltRounds, function(err, hash) {
        let db = new sqlite3.Database("./database/InvoicingApp.db");
        let sql = `INSERT INTO users(name,email,company_name,password) VALUES('${
          req.body.name
        }','${req.body.email}','${req.body.company_name}','${hash}')`;
        db.run(sql, function(err) {
          if (err) {
            throw err;
          } else {
            return res.json({
              status: true,
              message: "User Created"
            });
          }
        });
        db.close();
      });
    });

If an existing user tries to log in to the system using the /login route, they need to provide their email address and password. Once they do that, the route handles the request as follows:

    [...]

    app.post("/login", function(req, res) {
      let db = new sqlite3.Database("./database/InvoicingApp.db");
      let sql = `SELECT * from users where email='${req.body.email}'`;
      db.all(sql, [], (err, rows) => {
        if (err) {
          throw err;
        }
        db.close();
        if (rows.length == 0) {
          return res.json({
            status: false,
            message: "Sorry, wrong email"
          });
        }

      [...]

A query is made to the database to fetch the record of the user with a particular email. If the result returns an empty array, then it means that the user doesn’t exist and a response is sent informing the user of the error.

If the database query returns user data, a further check is made to see if the password entered matches that password in the database. If it does, then a response is sent with the user data.

      [...]
        let user = rows[0];
        let authenticated = bcrypt.compareSync(req.body.password, user.password);
        delete user.password;
        if (authenticated) {
          return res.json({
            status: true,
            user: user
          });
        }
        return res.json({
          status: false,
          message: "Wrong Password, please retry"
        });
      });
    });

    [...]

When the route is tested, you will receive either a successful or failed result.

The /invoice route handles the creation of an invoice. Data passed to the route will include the user ID, name of the invoice, and invoice status. It will also include the singular transactions to make up the invoice.

The server handles the request as follows:

    [...]
    app.post("/invoice", multipartMiddleware, function(req, res) {
      // validate data
      if (isEmpty(req.body.name)) {
        return res.json({
          status: false,
          message: "Invoice needs a name"
        });
      }
      // perform other checks

      [...]

First, the data sent to the server is validated. Then a connection is made to the database for the subsequent queries.

      [...]
      // create invoice
      let db = new sqlite3.Database("./database/InvoicingApp.db");
      let sql = `INSERT INTO invoices(name,user_id,paid) VALUES(
        '${req.body.name}',
        '${req.body.user_id}',
        0
      )`;
      [...]

The INSERT query needed to create the invoice is written and then executed. Afterwards, the singular transactions are inserted into the transactions table with the invoice_id as foreign key to reference them.

      [...]
      db.serialize(function() {
        db.run(sql, function(err) {
          if (err) {
            throw err;
          }
          let invoice_id = this.lastID;
          for (let i = 0; i < req.body.txn_names.length; i++) {
            let query = `INSERT INTO transactions(name,price,invoice_id) VALUES(
                '${req.body.txn_names[i]}',
                '${req.body.txn_prices[i]}',
                '${invoice_id}'
            )`;
            db.run(query);
          }
          return res.json({
            status: true,
            message: "Invoice created"
          });
        });
      });
    [...]

Once this is executed, the invoice is successfully created.

On checking the SQLite database, the following result is obtained:

    sqlite> select * from invoices;
    1|Test Invoice New|2|0
    sqlite> select * from transactions;
    1|iPhone|600|1
    2|Macbook|1700|1

Now, when a user wants to see all the created invoices, the client will make a GET request to the /invoice/user/:id route. The user_id is passed as a route parameter. The request is handled as follows:

      [...]
    app.get("/invoice/user/:user_id", multipartMiddleware, function(req, res) {
      let db = new sqlite3.Database("./database/InvoicingApp.db");
      let sql = `SELECT * FROM invoices LEFT JOIN transactions ON invoices.id=transactions.invoice_id WHERE user_id='${req.params.user_id}'`;
      db.all(sql, [], (err, rows) => {
        if (err) {
          throw err;
        }
        return res.json({
          status: true,
          transactions: rows
        });
      });
    });

    [...]

A query is run to fetch all the invoices and the transactions related to the invoice belonging to a particular user.

To fetch a specific invoice, a GET request is made with the user_id and invoice_id to the /invoice/user/{user_id}/{invoice_id} route. The request is handled as follows:

    [...] 

    app.get("/invoice/user/:user_id/:invoice_id", multipartMiddleware, function(req, res) {
      let db = new sqlite3.Database("./database/InvoicingApp.db");
      let sql = `SELECT * FROM invoices LEFT JOIN transactions ON invoices.id=transactions.invoice_id WHERE user_id='${
        req.params.user_id
      }' AND invoice_id='${req.params.invoice_id}'`;
      db.all(sql, [], (err, rows) => {
        if (err) {
          throw err;
        }
        return res.json({
          status: true,
          transactions: rows
        });
      });
    });

    // set application port
    [...]

A query is ran to fetch a single invoice and the transactions related to the invoice belonging to the user.

Conclusion

In this tutorial, you set up your server with all the needed routes for a lightweight invoicing application.