Angular command bus

Implementation command bus pattern with the support middleware as Angular module

Installation

npm install angular-command-bus --save

Configuration

Module

@NgModule({
  imports: [
      CommandBusModule.forRoot()
  ]
})
export class AppModule {
}

Example

Model

export class Order {
    constructor(private id: string, private name: string) {}
}

Command

export class CreateOrderCommand {
    constructor(readonly orderId: string, readonly name: string) {}
}

Handler

export class CreateOrderHandler implements CommandHandler {
    constructor(orderService: OrderService) {}
    
    handle(command: CreateOrderCommand) {
        const order = new Order(command.orderId, command.name);
        orderService.save(order);
    }
    
    supportsCommand(): string {
        return CreateOrderCommand.name;
    }
}

Component

@Component({
  selector: 'app-orders-page',
  templateUrl: './orders-page.component.html',
  styleUrls: ['./orders-page.component.scss']
})
export class OrdersPageComponent {
    constructor(private commandBus: CommandBus) {}
    
    onSubmit() {
        this.commandBus.handle(new CreateOrderCommand(id, name));
    }
}

Adding middleware

This is a kind of pattern Intercepting filter from Core J2EE Patterns

@NgModule({
  providers: [
      {provide: COMMAND_BUS_MIDDLEWARE, useClass: LoggingMiddleware, multi: true},
      {provide: COMMAND_BUS_MIDDLEWARE, useClass: AuthorizationMiddleware, multi: true}
  ]
})
export class AppModule {
}

Middleware class

export class LoggingMiddleware implements CommandBusMiddleware {
    /*
     * @param next this is a reference for next middleware function
     */
    handle(command, next) {
        // before code
        next(command);
        // after code
    }
}

if 'next' is not called, the processing of the command will be completed and further middleware, as well as the command handler, will not be executed.

For example AuthorizationMiddleware

export class AuthorizationMiddleware implements CommandBusMiddleware {
    constructor(
        private userService: UserService,
        private notificationService: NotificationService
    ) {}
    
    handle(command, next) {
        if (!userService.hasRole('ROLE_ADMIN')) {
            notificationService.alert(
                'Access denied for handle command ' + command.constructor.name
            );
            return;
        }
        
        next(command);
    }
}