Proposal: Hierarchical module resolution

[aigoncharov]

I'm submitting a...

[ ] Regression 
[ ] Bug report
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

Currently all lifecycle hooks run asynchronously, regardless of their importing order. If any module depends on an async provider it has to import a module this provider belongs to and then import the provider itself to wait for it being resolved.

Expected behavior

It feels natural for any module to wait for its dependencies' initialization before its own initialization. I propose to build a hierarchy of modules and resolve the resulting tree starting from its children. It should work in reverse with module destruction. First top level modules are destroyed, then children.

const sleep = (time: number) => new Promise((resolve, reject) => setTimeout(resolve, time))

@Module()
class B  implements OnModuleInit, OnModuleDestroy  {
  public async onModuleDestroy () {
    await sleep(1000)
    console.log('B destroyed')
  }
  public async onModuleInit () {
    await sleep(1000)
    console.log('B initialized')
  }
}

@Module({
  imports: [ B ]
})
class A  implements OnModuleInit, OnModuleDestroy  {
  public async onModuleDestroy () {
    await sleep(1000)
    console.log('A destroyed')
  }
  public async onModuleInit () {
    await sleep(1000)
    console.log('A initialized')
  }
}

I want Nest to guarantee that when A is created B.onModuleInit runs before A.onModuleInit and when it's destroyed that A.onModuleDestroy runs before B.onMOduleDestroy

What is the motivation / use case for changing the behavior?

Imagine your application having ThirdPartyLib module. It calls function thirdPartyLibInit using FFI to initialize a C-callable library on creation. Imagine your application having controller MyController depending on ThirdPartyLib. It can not function properly without that C-callable library initialized. Now you have to create an async factory that makes that FFI call and inject it everywhere. It's not very clean. I'd like to be able to import ThirdPartyLib into MyController and leave it up to Nest to figure it out.

[aigoncharov]

Relates to #550

[kamilmysliwiec]

solved by #977

[aigoncharov]

@kamilmysliwiec you are the man! Thank you!

[kamilmysliwiec]

Thanks! Gonna leave it open until 5.2.0 is published :)

[kamilmysliwiec]

5.2.0 is here!

[jBouyoud]

As I experiment lifecycle event are not called in special order (before all non global modules for OnModuleInit, after all non global modules for OnModuleDestroy).
It is an intent or a bug, I don't find anything in our doc about global module and lifecycle event ?

Thanks

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.