Execution Context

There are several ways of mounting the Nest application. You can create either a web app, microservice or just a Nest execution context. The Nest context is a wrapper around the Nest container, which holds all instantiated classes. We can grab an existing instance from within any imported module directly using application object. Thanks to that, you can take advantages of the Nest framework everywhere, including CRON jobs and even build a CLI on top of it.

Getting started

In order to create a Nest application context, we use the following syntax:

async function bootstrap() {
  const app = await NestFactory.createApplicationContext(ApplicationModule);
  // logic...
}
bootstrap();

Afterward, Nest allows you to pick any instance registered within Nest application. Let's imagine that we have a TasksController in the TasksModule. This class provides a set of usable methods, which we want to call from within CRON job.

const app = await NestFactory.create(ApplicationModule);
const tasksController = app.get(TasksController);

And that's it. To grab TasksController instance we had to use get() method. We didn't have to go through entire modules tree, the get() method act like a query that search for an instance in each registered module automatically. However, if you prefer a strict context checking, you can always switch to it using strict: true options object that has to be passed as the second argument of get() method. Then, you have to go through all modules to pick up a particular instance from the selected context.

const app = await NestFactory.create(ApplicationModule);
const tasksController = app.select(TasksModule).get(TasksController, { strict: true });

Hint The root module is selected by default. In order to select any other module, you need to go through entire modules tree (step by step).