Initialization

In many situations, we need to initialize the application (i.e perform certain actions) before listening to incoming HTTP requests. This is the case, for example, if you need to establish a connection to the database.

There are three ways to achieve this in FoalTS.

The main function

The most straightforward way to do it, which is used by default, is to add the initialization commands in the main function before createApp is called.

If your application uses TypeORM, your project should have a file src/index.ts that looks like this:

async function main() {
  // Initialization
  await createConnection();

  // Creation of the application
  const app = createApp(AppController);

  // ...
}

main();

The AppController.init method

Sometimes, however, this approach is not sufficient because we need to call the methods of some services. In this case, you can add an init method to the root controller class which will be called before the application is fully created. This method can be synchronous or asynchronous.

Example 1

export class AppController {

  @dependency
  serviceA: ServiceA;

  async init() {
    await this.serviceA.doSomething();
  }

}

Example 2

export class AppController {

  @dependency
  serviceA: ServiceA;

  @dependency
  serviceB: ServiceB;

  async init() {
    this.serviceA.init();
    this.serviceB.init();
  }

}

For this to work, you need to update your src/index.ts file and create the application with the asynchronous function createAndInitApp.

import { createAndInitApp } from '@foal/core';

async function main() {
  const app = await createAndInitApp(AppController);

  // ...
}

main();

The services boot method

boot methods are available in v1.8.0 onwards.

Alternatively you can add a boot method in your services. This method can be synchronous or asynchronous.

Example

export class ServiceA {

  async boot() {
    await doSomething();
  }

}

Then, you have to call the boot method of your service manager (it will be automatically called starting from version 2).

import { createAndInitApp } from '@foal/core';

async function main() {
  const serviceManager = new ServiceManager();
  const app = createApp(AppController, {
    serviceManager
  });
  // This line calls the `boot` method of all your services that have one.
  await serviceManager.boot();

  // ...
}

main();

If you manually inject services to your service manager and you want their boot methods to be called, you must specify this in the set method options.

const serviceManager = new ServiceManager();
serviceManager.set(ServiceA, myServiceInstance, { boot: true })

Best Practices

If your initialization consists of several asynchronous tasks, you may want to perform them in parallel. This will reduce the initialization time, which has an impact if you use a serverless architecture.

export class AppController {

  async init() {
    // Don't do
    await createConnection();
    await createAnotherConnection();

    // Do
    await Promise.all([
      createConnection(),
      createAnotherConnection()
    ])
  }

}