Queue producers in NestJS - Mini Project: Build & Apply

Queue Producers with NestJS

📖 Scenario: You are building a simple NestJS application that sends messages to a queue system. This is common in real-world apps where tasks are processed asynchronously, like sending emails or processing orders.

🎯 Goal: Create a NestJS queue producer that sends messages to a queue named task_queue. You will set up the data, configure the queue name, implement the message sending logic, and complete the producer service.

📋 What You'll Learn

Create a message object with specific content

Define a queue name variable

Implement a method to send the message to the queue

Complete the NestJS service class with the producer logic

💡 Why This Matters

🌍 Real World

Queue producers are used in applications to send tasks or events to be processed asynchronously, improving performance and user experience.

💼 Career

Understanding how to create queue producers is essential for backend developers working with microservices, event-driven architectures, and scalable systems.

1

Create the message data

Create a constant object called message with the exact properties: { taskId: 101, taskName: 'SendEmail' }.

NestJS

# Create the message object
# Your code here

Hint

Use const to create an object named message with the given properties.

2

Define the queue name

Add a constant string variable called queueName and set it exactly to 'task_queue'.

NestJS

const message = { taskId: 101, taskName: 'SendEmail' };
# Define the queue name
# Your code here

Hint

Use const queueName = 'task_queue'; to define the queue name.

3

Implement the sendMessage method

Inside a NestJS service class, write a method called sendMessage that takes no parameters and calls this.queueClient.send(queueName, message) to send the message.

NestJS

const message = { taskId: 101, taskName: 'SendEmail' };
const queueName = 'task_queue';

export class QueueProducerService {
  constructor(private readonly queueClient: any) {}

  // Implement sendMessage method
  # Your code here
}

Hint

Define sendMessage() method that calls this.queueClient.send(queueName, message);

4

Complete the producer service

Add the @Injectable() decorator above the QueueProducerService class to complete the NestJS service setup.

NestJS

const message = { taskId: 101, taskName: 'SendEmail' };
const queueName = 'task_queue';

// Add @Injectable decorator below
# Your code here
export class QueueProducerService {
  constructor(private readonly queueClient: any) {}

  sendMessage() {
    this.queueClient.send(queueName, message);
  }
}

Hint

Import and add @Injectable() decorator above the class to make it a NestJS service.

Practice

1. What is the main role of a queue producer in a NestJS application?

easy

A. To monitor the queue status and logs

B. To process tasks received from the queue

C. To delete completed tasks from the queue

D. To send tasks or messages to a queue for later processing

Solution

1. Step 1: Understand the role of queue producer

   A queue producer is responsible for sending tasks or messages to a queue, not processing them.

2. Step 2: Differentiate producer from consumer

   Consumers process tasks, while producers only add tasks to the queue.

3. Final Answer:

   To send tasks or messages to a queue for later processing -> Option D

4. Quick Check:

   Queue producer = sends tasks [OK]

Hint: Producers add tasks; consumers process them [OK]

Common Mistakes:

• Confusing producer with consumer
• Thinking producer processes tasks
• Assuming producer deletes tasks

2. Which of the following is the correct way to inject a queue named 'email' in a NestJS producer service?

easy

A. @InjectQueue('email') emailQueue: Queue = new Queue();

B. @InjectQueue private emailQueue: Queue('email');

C. @InjectQueue('email') private readonly emailQueue: Queue;

D. @InjectQueue('email') private emailQueue = Queue;

Solution

1. Step 1: Recall correct syntax for @InjectQueue

   The decorator requires the queue name as a string and the property must be typed as Queue.

2. Step 2: Check property declaration

   It should be private readonly with type Queue, no manual instantiation needed.

3. Final Answer:

   @InjectQueue('email') private readonly emailQueue: Queue; -> Option C

4. Quick Check:

   @InjectQueue('name') private readonly queue: Queue [OK]

Hint: Use @InjectQueue('name') private readonly queue: Queue [OK]

Common Mistakes:

• Missing private or readonly keywords
• Trying to instantiate Queue manually
• Incorrect decorator usage without queue name

3. Given the following code snippet in a NestJS producer service, what will be the output when sendEmail() is called?

async sendEmail() {
  await this.emailQueue.add('send_email', { to: '[e-mail]' });
  return 'Email task added';
}

medium

A. An error because 'send_email' is not a valid job name

B. 'Email task added'

C. The email is sent immediately

D. Nothing happens because add() is asynchronous

Solution

1. Step 1: Understand queue.add() behavior

   The add() method adds a job to the queue asynchronously but does not send the email immediately.

2. Step 2: Check return value of sendEmail()

   After adding the job, the function returns the string 'Email task added'.

3. Final Answer:

   'Email task added' -> Option B

4. Quick Check:

   queue.add() adds job, function returns confirmation [OK]

Hint: queue.add() adds job; function returns confirmation string [OK]

Common Mistakes:

• Assuming add() sends email immediately
• Thinking add() returns error for job name
• Ignoring async nature of add()

4. Identify the error in this NestJS queue producer code:

@Injectable()
export class NotificationProducer {
  constructor(@InjectQueue('notifications') private notificationsQueue: Queue) {}

  async sendNotification(data: any) {
    this.notificationsQueue.add('notify', data);
  }
}

medium

A. Missing await before this.notificationsQueue.add()

B. Incorrect queue name in @InjectQueue decorator

C. sendNotification should not be async

D. notificationsQueue should be public, not private

Solution

1. Step 1: Check async method usage

   The add() method returns a promise, so it should be awaited inside an async function to handle completion properly.

2. Step 2: Verify other parts

   The queue name and access modifiers are correct; async keyword is appropriate.

3. Final Answer:

   Missing await before this.notificationsQueue.add() -> Option A

4. Quick Check:

   Async add() needs await to handle promise [OK]

Hint: Always await queue.add() inside async methods [OK]

Common Mistakes:

• Forgetting await on async queue.add()
• Changing queue name incorrectly
• Removing async keyword unnecessarily

5. You want to create a NestJS queue producer that sends different types of jobs to the same queue with different priorities. Which approach correctly implements this?

hard

A. Use queue.add(jobName, data, { priority: number }) to set priority per job

B. Create multiple queues with different names for each priority level

C. Set priority globally on the queue during injection with @InjectQueue

D. Use queue.add(jobName, data) and sort jobs manually later

Solution

1. Step 1: Understand job priority in queues

   Queue jobs can have individual priorities set when added, using options like { priority: number }.

2. Step 2: Evaluate options

   Creating multiple queues or setting priority globally is not the recommended way; manual sorting is inefficient.

3. Final Answer:

   Use queue.add(jobName, data, { priority: number }) to set priority per job -> Option A

4. Quick Check:

   Set priority per job with add() options [OK]

Hint: Set priority in add() options per job [OK]

Common Mistakes:

• Trying to set priority globally on queue
• Creating many queues instead of one
• Ignoring built-in priority support