Unlocking the Power of Event-Driven Programming
When it comes to building software, most developers rely on the request/response mechanism with layered architecture (n-tier) beneath. While this approach has its advantages, it’s not a one-size-fits-all solution. In fact, some software can be written more expressively using alternative design patterns.
The Limitations of Layered Architecture
Layered architecture is great for small and medium-sized projects, but it can become unwieldy and lead to “Baklava code” if not managed properly. This is where event-driven programming comes in – a paradigm that’s perfect for highly asynchronous systems that don’t require an immediate response from the server.
The Magic of Event-Driven Programming
In event-driven programming, one event can trigger multiple actions, making it ideal for building user interfaces. But it’s not limited to front-end development; it can also be used for writing server-side code. By using event-driven programming, you can add new features without editing existing components, making it a highly scalable and maintainable approach.
Implementing CQRS Design Patterns
To demonstrate the power of event-driven programming, we’ll implement CQRS (Command Query Responsibility Segregation) design patterns. This approach divides code into commands (actions that edit data) and queries (actions that read data). Our application will consist of:
- Commands: Actions that trigger business logic or dispatch new events
- Handlers: Responsible for executing commands
- Events: Used to dispatch other commands
- Queries: Actions that read data
A Real-World Example: Bidding System
Let’s imagine a bidding system where one action can trigger other actions in a defined order. We’ll create a system that:
- Checks if a bid is the highest one
- Sends email notifications to interested parties
- Adds a bid to the database
- Creates an activity for that bid
- Extends the bidding process for two hours upon receiving the latest bid
How It Works
Each event will produce one or more commands, which will trigger new events. This event-driven system enables aspect-oriented programming, allowing you to add new functionality without changing existing code.
Nestjs: A Framework for Event-Driven Programming
We’ll use Nestjs to implement our bidding system, leveraging its CQRS module. Nestjs offers a rich ecosystem, including EventBus, QueryBus, and CommandBus, making it easy to trigger events, queries, and commands.
The Code
Our code will consist of a main controller that dispatches BidEvent, which will trigger BidCommand. The real power lies in the BidSaga class, responsible for listening to BidEvents and dispatching commands. With Nestjs, we can create a scalable and maintainable system that’s easy to extend.
Try It Out
Check out the full code and working demo on Github. With event-driven programming and CQRS design patterns, you can create highly scalable and maintainable systems that are perfect for complex applications.