Life-cycle-observer-generator.md

lang	en
title	Life cycle observer generator
keywords	LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI
sidebar	lb4_sidebar
permalink	/doc/en/lb4/Life-cycle-observer-generator.html

{% include content/generator-create-app.html lang=page.lang %}

Synopsis

Adds a new LifeCycleObserver class to a LoopBack application.

lb4 observer [--group <group>] [<name>]

Arguments and options

<name> - Required name of the observer to create as an argument to the command. If provided, the tool will use that as the default when it prompts for the name.

--group <group> - Optional name of the observer group to sort the execution of observers by group.

Interactive Prompts

The tool will prompt you for:

• Name of the observer. (observerName) If the name had been supplied from the command line, the prompt is skipped.

• Group of the observer. (groupName) If the group had been supplied from the command line, the prompt is skipped.

Output

Once all the prompts have been answered, the CLI will do the following:

• Create a LifeCycleObserver class as follows: /src/observers/${observerName}.observer.ts
• Update /src/observers/index.ts to export the newly created LifeCycleObserver class.

The generated class looks like:

import {
  /* inject, Application, CoreBindings, */
  lifeCycleObserver, // The decorator
  CoreTags,
  LifeCycleObserver, // The interface
} from '@loopback/core';

/**
 * This class will be bound to the application as a `LifeCycleObserver` during
 * `boot`
 */
@lifeCycleObserver('observer-group-name')
export class HelloObserver implements LifeCycleObserver {
  /*
  constructor(
    @inject(CoreBindings.APPLICATION_INSTANCE) private app: Application,
  ) {}
  */

  /**
   * This method will be invoked when the application initializes. It will be
   * called at most once for a given application instance.
   */
  async init(): Promise<void> {
    // Add your logic for init
  }

  /**
   * This method will be invoked when the application starts.
   */
  async start(): Promise<void> {
    // Add your logic for start
  }

  /**
   * This method will be invoked when the application stops.
   */
  async stop(): Promise<void> {
    // Add your logic for start
  }
}