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There are various types of artifacts being added to the application, such as controller, interceptor, observer. Such artifacts need to be loaded and registered with the application so that they can be used for composition. It can be achieved by calling Context APIs or helper methods on the application object:

import {createBindingFromClass, BindingScope} from '@loopback/core';
import {CACHING_SERVICE} from './keys';
import {CachingService} from './caching-service';
import {GreetingController} from './controllers';
import {CachingObserver} from './observers';
import {CachingInterceptor} from './interceptors';
// Use a helper method
app.controller(GreetingController);
// Use bind directly
app.bind(CACHING_SERVICE).toClass(CachingService).scope(BindingScope.SINGLETON);
// Use a helper method
app.lifeCycleObserver(CachingObserver);
// Use a helper method to create bindings and add them to the application
app.add(createBindingFromClass(CachingObserver));
app.add(createBindingFromClass(CachingInterceptor));

As the number of artifacts increases over time, it becomes cumbersome and error-prone. A better and simpler way is to use boot.

Use @loopback/boot

The BootMixin adds boot() to your application. The new code looks much simpler:

import {BootMixin} from '@loopback/boot';
import {ApplicationConfig} from '@loopback/core';
import {RestApplication} from '@loopback/rest';
import {GreetingComponent} from './component';
import {CACHING_SERVICE} from './keys';
import {CachingService} from './caching-service';
export class GreetingApplication extends BootMixin(RestApplication) {
  constructor(config: ApplicationConfig = {}) {
    super(config);
    // Set up the root of the project for booting
    this.projectRoot = __dirname;
    this.add(createBindingFromClass(CachingService, {key: CACHING_SERVICE}));
    this.component(GreetingComponent);
  }
  async main() {
    // Discover, load, and bind artifacts by convention
    await this.boot();
    await this.start();
  }
}

greeting-app boot

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