Event Bus

The Nimbus event bus allows to publish and subscribe to events within the application.

Example Application

You can find the full example on GitHub The Expense Repo

Check it out and run it with deno task dev

Event Subscriptions

To set up event subscriptions, we want to create a new instance of the NimbusEventBus first. Then we want to use the subscribeEvent method to subscribe to all the events the application needs to handle.

In the main.ts file we call the initEventBusSubscriptions function to subscribe to all the events for the different domains when the application starts.

eventBus.ts

import { NimbusEventBus, RouteHandlerMap } from "@nimbus/core";
import { accountEventSubscriptions } from "./account/shell/account.eventBus.ts";

//
// Create a new instance of the event bus
//
export const eventBus = new NimbusEventBus({
    maxRetries: 3,
});

//
// Create a function that subscribes to all
// the events for the different domains
//
export const initEventBusSubscriptions = () => {
    const subscriptions: Record<string, RouteHandlerMap> = {
        account: accountEventSubscriptions,
    };

    for (const [, handlerMap] of Object.entries(subscriptions)) {
        for (const eventName of Object.keys(handlerMap)) {
            eventBus.subscribeEvent(
                eventName,
                handlerMap[eventName].inputType,
                handlerMap[eventName].handler
            );
        }
    }
};

account.eventBus.ts

import { RouteHandlerMap } from "@nimbus/core";
import { AccountAddedEvent } from "../core/events/accountAdded.ts";
import { accountAddedHandler } from "./events/accountAdded.handler.ts";

export const accountEventSubscriptions: RouteHandlerMap = {
    ACCOUNT_ADDED: {
        handler: accountAddedHandler,
        inputType: AccountAddedEvent,
    },
};

main.ts

import { initEventBusSubscriptions } from "./eventBus.ts";

initEventBusSubscriptions();

Publish Events

To publish an event, we can use the putEvent method of the NimbusEventBus class.

import { eventBus } from "../../../eventBus.ts";
import { AccountAddedEvent } from "../../core/events/accountAdded.ts";

eventBus.putEvent<AccountAddedEvent>({
    name: "ACCOUNT_ADDED",
    data: {
        account: account,
    },
    metadata: {
        correlationId: command.metadata.correlationId,
        authContext: command.metadata.authContext,
    },
});