@beetech/cqrs

Bee CQRS

This is a simple CQRS framework with a Command and a Query bus.

Motivation

There are a lot of CQRS frameworks for JavaScript out there, this is not new. The one thing we're trying to achieve here is the ability to take advantage of such a framework but without coupling it into the application's domain. The main goal here is to create a framework that you can use without injecting any dependencies into your domains.

Getting started

Install it using npm:

npm install @beetech/cqrs

Usage

Let's use a coupled example to show how the types are glued together.

import { InMemoryHandlerRegistry, QueryBus, QueryHandler } from '@beetech/cqrs';

export class Multiplier {
    public constructor(
        public readonly value: number,
        public readonly factor: number,
    ) {}
}

export class MultiplierHandler implments QueryHandler<Multiplier, number> {
    public query(query: Multiplier): number {
        return query.value * query.factor;
    }
}

const registry = (new InMemoryHandlerRegistry<QueryHandler<any, any>>())
    .register('Multiplier', multiplierHandler);

const queryBus = new QueryBus(registry);
const result = queryBus.query(new Multiplier(5, 4));
// result should be equal to 20

You can see that MultiplierHandler is implementing an interface called QueryHandler, right? This is an example of a "coupled" implementation. Imagine this being used inside your domain, you'll have a domain importing an external library and that's not ideal.

By taking advantage of TypeScript's gererics, we were able to create a structure that will work event if you don't explicitly implements our interface. Here's the same example but not coupled:

import { InMemoryHandlerRegistry, QueryBus, QueryHandler } from '@beetech/cqrs';

export class Multiplier {
    public constructor(
        public readonly value: number,
        public readonly factor: number,
    ) {}
}

export class MultiplierHandler {
    public query(query: Multiplier): number {
        return query.value * query.factor;
    }
}

const registry = (new InMemoryHandlerRegistry<QueryHandler<any, any>>())
    .register('Multiplier', multiplierHandler);

const queryBus = new QueryBus(registry);
const result = queryBus.query(new Multiplier(5, 4));
// result should be equal to 20

As you can see, the query and the query handler have nothing to do with the CQRS framework, all the bindings will be where they belong: inside the application layer and not on the domain layer.

It's a subtle but, at the same time, huge difference.