Скачать или смотреть Harnessing rxjs with NestJS: A Timer to Manage Events in CQRS Sagas

Learn how to effectively manage event-driven scenarios in NestJS using `rxjs`, including handling event types and timers in CQRS sagas.
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Harnessing rxjs with NestJS: A Timer to Manage Events in CQRS Sagas

In the world of asynchronous programming, especially when working with event-driven architectures like CQRS in NestJS, managing multiple events can become quite tricky. A common scenario involves listening for events that set and unset values. In this guide, we will explore how to handle two rxjs observables—one for setting a value and another for unsetting it—with a timer feature that allows us to take action based on these events.

The Problem: Understanding Event Handling

Imagine a situation where two specific events are published in a sequence:

ValueHasBeenSet: This event sets a value.

ValueHasBeenUnset: This event clears the value that was set.

Your goal is to listen for the ValueHasBeenSet event for a duration of 3 seconds, during which if the ValueHasBeenUnset event occurs, you'll need to cancel any subsequent actions that you would have taken.

Furthermore, both events can have distinct value types associated with them. For instance, the property type within the events can either be 'blue' or 'yellow'. This complexity necessitates a careful approach to ensure that event types are distinct while using generic handlers.

The Solution: Implementing the Logic with RxJS

To address the scenario effectively, we can utilize the power of RxJS operators. Here’s a step-by-step breakdown of how you can implement this logic.

Step 1: Set Up Your Observable

We start by creating an observable that listens for the ValueHasBeenSet event:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Explanation of Key Operators

ofType: This operator filters out the events to capture only those of type ValueHasBeenSet.

switchMap: Used here to manage the inner observable created by the timer. This will switch the stream to the timer observable whenever a new ValueHasBeenSet event occurs.

timer(3000): This creates a timer that emits after 3 seconds, allowing us to perform a subsequent action.

takeUntil: This operator listens for the ValueHasBeenUnset event. If it occurs before the timer finishes, the observable is unsubscribed, effectively cancelling the pending action.

map: After the timer completes without interruption, we finally map our result to a new command.

Step 3: Handling Multiple Event Types

If you need to maintain the differentiation between the different event types (e.g., when the event has properties like 'type'), you can enhance the logic further. For example, you can use a more sophisticated strategy to handle events based on their specific characteristics or properties.

Conclusion

Using rxjs with NestJS in an event-driven architecture can significantly simplify the management of asynchronous events and complex logic like timers. With the outlined solution, you can effectively listen for setting and unsetting events while preserving the distinction between various value types.

By mastering these operators in RxJS, you can create robust applications that efficiently manage state based on event-driven scenarios.

This approach positions you well for developing scalable applications within the NestJS framework, harnessing the full power of reactive programming.