Asimov CQBus

Simple javascript/typescript command & query bus. For use in CQRS and Clean Architecture / Hexagonal projects.

Installation

Npm:

$ npm install --save asimov-cqbus

Yarn:

$ yarn add asimov-cqbus

Usage

Commands

class CreateFullName extends Command<string> {
    constructor(public firstName: string, public lastName: string) { super(); }
}

class CreateFullNameHandler implements RequestHandler<CreateFullName, string> {
    async handle(command: CreateFullName, identity: Identity): Promise<string> {
        return command.firstName + ' ' + command.lastName;
    }
}

const cqBus = new CQBus();
cqBus.registerHandler(CreateFullName, () => new CreateFullNameHandler());

const result = await cqBus.execute(new CreateFullName('John', 'Doe')); // returns 'John Doe'

Queries

class GetNews extends Query<string[]> {}

class GetNewsHandler implements RequestHandler<GetNews, string[]> {
    async handle(command: GetNews, identity: Identity): Promise<string[]> {
        return ['news 1', 'news 2'];
    }
}

const cqBus = new CQBus();
cqBus.registerHandler(GetNews, () => new GetNewsHandler());

const result = await cqBus.execute(new GetNews()); // returns 'news 1', 'news 2'

Execution Identity

class UserIdentity implements Identity {
    readonly isAuthenticated = true;
    readonly authenticationType = null;
    readonly roles = [];
    readonly properties = {};

    constructor(readonly name: string) {
    }
}

class MyCommand extends Command<string> {}

class MyCommandHandler implements RequestHandler<MyCommand, string> {
    async handle(command: MyCommand, identity: Identity): Promise<string> {
        return identity.name;
    }
}

const cqBus = new CQBus();
cqBus.registerHandler(MyCommand, () => new MyCommandHandler());

const context = ExecutionContext.empty().withIdentity(new UserIdentity('Alice'));
const result = await cqBus.execute(new MyCommand(), context); // returns 'Alice'

const result = await cqBus.execute(new MyCommand()); // returns 'Anonymous'

Context-aware handlers

class MyCommand extends Command<string> {}

class MyCommandHandler implements ContextAwareRequestHandler<MyCommand, string> {
    async handle(command: MyCommand, context: ExecutionContext): Promise<string> {
        return context.get(['some-key');
    }
}

const cqBus = new CQBus();
cqBus.registerContextAwareHandler(MyCommand, () => new MyCommandHandler());

const context = ExecutionContext.empty().with('some-key', 'some-value');
const result = await cqBus.execute(new MyCommand(), context); // returns 'some-value'

Middlewares

class MyCommand extends Command<string> {}

class MyCommandHandler implements ContextAwareRequestHandler<MyCommand, string> {
    async handle(command: MyCommand, identity: Identity): Promise<string> {
        return 'handler';
    }
}

class LoggingMiddleware implements Middleware {
    constructor(private log, private suffix = '') {}
    
    async exec<T extends Request<R>, R>(request: T, next: (T) => Promise<R>, context: ExecutionContext): Promise<R> {
        this.log.push('before' + this.suffix)
        const result = await next(request);
        this.log.push('after' + this.suffix)
        return result;
    }
}

const log = [];
const cqBus = new CQBus();
cqBus.registerHandler(MyCommand, () => new MyCommandHandler());
cqBus.registerMiddleware(new LoggingMiddleware(log, '1'));
cqBus.registerMiddleware(new LoggingMiddleware(log, '2'));

const result = await cqBus.execute(new MyCommand(), context);

// log contains 'before2', 'before1', 'handler', 'after1', 'after2'