How can I access a repository globally in loopback 4?

Question

I used loopback 4 to bootstrap my API application and developed some parts of it. Now I'm trying to access repositories outside the controllers and tried everything I could but didn't help. None of my searches did too. For example I have a controller in which I can access repo such way.

constructor(
@repository(UserRepository) public userRepository: UserRepository){}

But if it isn't a controller it won't work and I found out I had a wrong understanding about @repository and @inject decorators.

My Case: I want to run a cron-job to perform an update operation on database every day at a specific time. The thing is I think I should create a service or something like that to expose database operations so it can be accessible anywhere.

score 3 · Answer 1 · answered Jul 05 '21 at 20:48

The issue you're trying to tackle comes down to dependency injection. It's described at https://loopback.io/doc/en/lb4/Dependency-injection.html but that article does not explain how to create a separate class that works with dependency injection.

In short, in order to perform the dependency injection through decorators, LoopBack needs to be the one to construct the class you're writing, so that it can pick what you need from its Context. So, instead of writing new ClassSomething, it has to be @inject(ClassSomething) or @service(ClassSomething), and those decorators only work in a class also instantiated by LoopBack. In other words, your class has to be in the "call tree" from the original application class (application.ts) for dependency injection to work.

The easiest way to do what you want to do is to use LoopBack's Cron component: see https://loopback.io/doc/en/lb4/Running-cron-jobs.html. You could convert your class to a CronJob if it has no other purpose, or let the CronJob create an instance of your class. In the latter case, you need to bind your class to the application Context so that the CronJob can access it through decorators. You can do so in two ways:

Convert your class to a Service (see https://loopback.io/doc/en/lb4/Service.html and https://loopback.io/doc/en/lb4/Service-generator.html). If what your class does can be thought of as a service, this is the way to go.
Inject your class with: @service(MyServiceClass) myService: MyServiceClass
Directly bind your class to the application context, in application.ts: this.bind('MyClass').toClass(MyClass);
Inject your class with: @inject(MyClass) myClass: MyClass

The latter option is not best practice AFAIU as it does not adhere to IoC-principles (https://en.wikipedia.org/wiki/Inversion_of_control) - basically, by hard-coding the class binding in the application class, it is not exactly modular. When your class is converted to a service (and placed in src/services), it will automatically be added to the Context, meaning you can inject it everywhere using @service().

score 0 · Answer 2 · answered Jun 22 '22 at 07:45

I also experience the same(cron word). I couldn't find any solution still in the documentation. But still, I have achieved this in this way.

just call repository as like class with dependency in it. do this in your index.ts file where you start the application.

async function startCronJobs(app: SawLoopbackApplication) {
  const userRepo = app.repository(UserRepository);
  const userRepoInstance = await userRepo.getValue(app);
  const cron = new CronComponent(userInstance);

  //---- Exicute your cron here
  new CronJob('0 6 * * *', function () {
       cron.sendMorningMail()
     }).start();

  //---- Exicute your Second Cron
  new CronJob('0 8 * * 1', function () {
     cron.weeklyAppraisalsToAgent()
   }).start();
 }

call your cron in the functional component and execute a raw query to get the details from DB etc...

import {MysqlDataSource} from '../../datasources'
const query = `select * from accounts where IP="${ipAddress}" ORDER By 
createdAt DESC Limit 1`
const dataSource = new MysqlDataSource()
const accountDetails = await dataSource.execute(query)
console.log(accountDetails)

instead of a raw query. call your repository from the function component below

  import {MysqlDataSource} from '../datasources'
  import {ContactUsUserDetailsRepository} from '../repositories'
  const contactUsUserDetailsRepository = new ContactUsUserDetailsRepository(new MysqlDataSource)
   function saveContactDetails(){
       const payload={UID:"Unique ID",name:"Durai"}
       await contactUsUserDetailsRepository.create(payload)
    }

I would prefer 2 because, if you have a lot of imports in your cron class constractor you need to pass all of them while calling a function like in the 3rd point.

Have fun:)

How can I access a repository globally in loopback 4?

2 Answers2