Mastering Logic Flow: Send Email Notifications when Product Quantity Hits the Desired Level with NestJS

Are you struggling to implement a seamless logic flow for sending email notifications when your product quantity reaches a desired level? Look no further! In this comprehensive guide, we’ll walk you through the process of creating an efficient email notification system using NestJS. By the end of this article, you’ll be equipped with the knowledge to automate email notifications and take your e-commerce game to the next level.

Understanding the Problem Statement

We’ve all been there – stuck trying to figure out why our email notifications aren’t firing off when product quantities dip below a certain threshold. It’s frustrating, to say the least. But fear not, dear developer! With NestJS, we can create a robust and scalable solution to tackle this issue once and for all.

The Desired Outcome

Our ultimate goal is to send an email notification to relevant stakeholders when the product quantity falls below or equals the desired quantity. This will ensure that our inventory management system is always on top of things, and our customers receive timely updates about product availability.

Setting Up the Project

Before we dive into the juicy logic flow stuff, let’s get our project set up. Create a new NestJS project using the following command:

npx @nestjs/cli new email-notification-app

Next, navigate into the project directory and install the required dependencies:

npm install --save @nestjs/microservices

We’ll be using the @nestjs/microservices package to handle our email notifications.

Defining the Logic Flow

Now that our project is set up, let’s define the logic flow for sending email notifications. We’ll break it down into three main steps:

1. Product Quantity Check: We’ll create a function to check the current product quantity and compare it to the desired quantity.
2. Email Notification Trigger: If the product quantity is less than or equal to the desired quantity, we’ll trigger the email notification process.
3. Email Notification Service: We’ll create a separate service to handle the email notification process, including sending the actual email.

Product Quantity Check Function

Create a new file called product.service.ts and add the following code:

import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { Product } from './product.entity';

@Injectable()
export class ProductService {
  constructor(
    @InjectRepository(Product)
    private readonly productRepository: Repository<Product>,
  ) {}

  async checkProductQuantity(productId: number, desiredQuantity: number): Promise<boolean> {
    const product = await this.productRepository.findOne(productId);
    if (!product) {
      throw new Error('Product not found');
    }
    return product.quantity <= desiredQuantity;
  }
}

This function takes two parameters: productId and desiredQuantity. It retrieves the product entity from the database and checks if the current quantity is less than or equal to the desired quantity. If true, it returns a boolean value indicating that the notification should be triggered.

Email Notification Trigger

Create a new file called email.trigger.ts and add the following code:

import { Injectable } from '@nestjs/common';
import { ProductService } from './product.service';

@Injectable()
export class EmailTrigger {
  constructor(private readonly productService: ProductService) {}

  async triggerEmailNotification(productId: number, desiredQuantity: number): Promise<void> {
    const shouldTrigger = await this.productService.checkProductQuantity(productId, desiredQuantity);
    if (shouldTrigger) {
      // Trigger email notification service
      console.log('Email notification triggered!');
    }
  }
}

This service imports the ProductService and calls the checkProductQuantity function to determine whether the email notification should be triggered. If true, it logs a message to the console indicating that the email notification has been triggered.

Email Notification Service

Create a new file called email.service.ts and add the following code:

import { Injectable } from '@nestjs/common';
import * as nodemailer from 'nodemailer';

@Injectable()
export class EmailService {
  private transporter: nodemailer.Transporter;

  constructor() {
    this.transporter = nodemailer.createTransport({
      host: 'your-smtp-host',
      port: 587,
      secure: false, // or 'STARTTLS'
      auth: {
        user: 'your-email-username',
        pass: 'your-email-password',
      },
    });
  }

  async sendEmailNotification(to: string, subject: string, message: string): Promise<void> {
    const mailOptions = {
      from: 'your-email-username',
      to,
      subject,
      text: message,
    };
    await this.transporter.sendMail(mailOptions);
  }
}

This service uses the nodemailer package to create a transporter instance, which we’ll use to send email notifications. The sendEmailNotification function takes three parameters: to, subject, and message. It uses the transporter instance to send the email notification.

Wiring it all Together

Now that we have our logic flow components ready, let’s wire them together. Create a new file called app.service.ts and add the following code:

import { Injectable } from '@nestjs/common';
import { EmailService } from './email.service';
import { EmailTrigger } from './email.trigger';

@Injectable()
export class AppService {
  constructor(private readonly emailService: EmailService, private readonly emailTrigger: EmailTrigger) {}

  async handleProductQuantity(productId: number, desiredQuantity: number): Promise<void> {
    await this.emailTrigger.triggerEmailNotification(productId, desiredQuantity);
    if (await this.emailTrigger.shouldTriggerEmailNotification(productId, desiredQuantity)) {
      const to = 'recipient-email@example.com';
      const subject = 'Product Quantity Alert';
      const message = `Product ${productId} has reached a quantity of ${desiredQuantity} or less.`;
      await this.emailService.sendEmailNotification(to, subject, message);
    }
  }
}

This service imports the EmailService and EmailTrigger instances. It defines a handleProductQuantity function that takes two parameters: productId and desiredQuantity. It triggers the email notification process by calling the triggerEmailNotification function, and then checks if the notification should be sent. If true, it sends the email notification using the EmailService.

Testing the Logic Flow

Let’s create a test case to verify that our logic flow is working as expected. Create a new file called app.test.ts and add the following code:

import { Test, TestingModule } from '@nestjs/testing';
import { AppService } from './app.service';
import { ProductService } from './product.service';
import { EmailTrigger } from './email.trigger';
import { EmailService } from './email.service';

describe('AppService', () => {
  let appService: AppService;
  let productService: ProductService;
  let emailTrigger: EmailTrigger;
  let emailService: EmailService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [AppService, ProductService, EmailTrigger, EmailService],
    }).compile();

    appService = module.get(AppService);
    productService = module.get(ProductService);
    emailTrigger = module.get(EmailTrigger);
    emailService = module.get(EmailService);
  });

  it('should send email notification when product quantity reaches desired level', async () => {
    const productId = 1;
    const desiredQuantity = 10;
    jest.spyOn(productService, 'checkProductQuantity').mockReturnValue(true);
    jest.spyOn(emailService, 'sendEmailNotification').mockImplementation(() => Promise.resolve());
    await appService.handleProductQuantity(productId, desiredQuantity);
    expect(emailService.sendEmailNotification).toHaveBeenCalledTimes(1);
  });
});

This test case creates a mock implementation of the checkProductQuantity function to always return true, and a mock implementation of the sendEmailNotification function to resolve immediately. It then calls the handleProductQuantity function and expects the sendEmailNotification function to be called once.

Conclusion

And that’s it! You now have a comprehensive guide on how to implement logic flow for sending email notifications when product quantities hit the desired level using NestJS. By following this tutorial, you should be able to create a robust and scalable email notification system that integrates seamlessly with your e-commerce application.

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