@mszmaj/mediatsion

mediaTSion

An in-process mediator/pipeline library for Typescript and NodeJS.

NOTE: Work in progress

Pre-requisites

IMPORTANT: reflect-metadata must be imported at the start of the application and only once.

Packages

Install reflect-metadata:

npm install reflect-metadata

Install mediatsion:

npm install mediatsion

How-To:

1A. Create new Request:

class ExampleRequest implements IRequest<ExampleInput, ExampleResult> {
    request: ExampleInput = new ExmapleInput();
    result: ExampleResult = new ExampleResult();
}

class ExampleInput implements IInput {
    example: string;
}

class ExampleResult implements IResult {
    id: string;
}

1B. Create new Event:

class ExampleEvent implements IEvent {
    example: string
}

2A. Create a new Command/Request Handler:

@requestHandler('ExampleRequest','ExampleResult')
class ExampleCommandHandler implements IRequestHandler<ExampleRequest, ExampleResult>  {
    async handleAsync(): Promise<Result<ExampleResult, Error>> {
        let result: Result<ExampleResult, Error>;
        try {
            //do stuff
            result = Ok(returnModel);
        } catch (error) {
            result = Err(new Error());
        } 
        
        return result;
    }
}

NOTE: Currently you need to pass in the name of the Request and Result objects as strings.

NOTE: The name of the handler; while it is a IRequestHandler it might be best to name it either *CommandHandler or *QueryHandler for readability. Typically Commands will not provide a Result object.

2B. Create a new Event handler:

@eventHandler('ExampleEvent')
class ExampleEventHandler implements IEventHandler<ExampleEvent>  {
    async handleAsync(): Promise<void> {
        //do stuff
    }
}

NOTE: Currently you need to pass in the name of the Event object as a string.

3. Use Bus to mediate:

import { Bus } from mediatsion;

const bus: Bus = new Bus();
const exampleRequestHandler = new ExampleRequestHandler();
const requestResult = await bus.send(exampleRequestHandler);

const exampleEvent = new ExampleEvent;
const eventResult = await bus.publish(exampleEvent); //NOTE: this will always be a void array. Only check for result.ok.

3A. Create a publish strategy:

A strategy will allow you to run event handlers in a different order than registered. This will allow you to run them in parallel as well.

const strategy = async (handlers: IEventHandler<TestEvent>[], event: IEvent): Promise<Array<void>> => {
        const result: Array<void> = [];
        for (let i = handlers.length-1; i >= 0; i--) {
            result.push(await handlers[i].handleAsync(event));
        }
        return result;
    }

const reuslt = await bus.publish(exampleEvent, strategy);

Release Notes:

0.1.2:

• Publish strategies

Roadmap:

0.1.3:

• Pipeline functionality

1.0.0:

• Production ready release