Nest: Cross modules dependency injection

Created on 20 Oct 2017 · 9Comments · Source: nestjs/nest

Suppose I have
Module A

Controller A
Component A
Module B
Controller B
Component B

If I want to use controller B in controller A, is dependency injection a good choice?
But in order to use dependency injection, I should do following in Module A:
controllers: [Controller A],
components: [Component A, Controller B, Component B]

Is it a good practice that references other module's controller in Module A for cross-module usage?

Thx.

Source

kwtsangaf

Most helpful comment

hey @kwtsangaf
if you want to use a component B in the controller A, you should exports the component B from the module B and then import the module B in the module A to use the component B in the controller A

// Module B
@Module({
    controllers: [ControllerB],
    components: [ComponentB],
    exports: [componentB]
})

// Module A
@Module({
    modules: [ModuleB],
    controllers: [ControllerA],
    components: [ComponentA]
})

// Controller A of the Module A
@Controller()
export class controllerA {
    constructor(private readonly componentB: ComponentB) { }
}

adrien2p on 20 Oct 2017

👍5

All 9 comments

@kwtsangaf I suppose you mixed things slightly - what do you mean when you say

want to use controller B in controller A

Did you mean use component B in controller A?

exfinder on 20 Oct 2017

// Module B
@Module({
    controllers: [ControllerB],
    components: [ComponentB],
    exports: [componentB]
})

// Module A
@Module({
    modules: [ModuleB],
    controllers: [ControllerA],
    components: [ComponentA]
})

// Controller A of the Module A
@Controller()
export class controllerA {
    constructor(private readonly componentB: ComponentB) { }
}

adrien2p on 20 Oct 2017

👍5

The controllers are responsible of the requests, so if you need Controller A inside controller B, perhaps you have so much application logic inside controller A. You should extract that logic to a component and inject that componen in controller A and controller B

jselesan on 20 Oct 2017

I think there is a miss understanding between controller and component in the question. maybe ^^

adrien2p on 20 Oct 2017

Am I the only one who thinks that having hierarchical injector is unnecessary and just makes things complex? I mean for Angular is ok and makes sense (lazy loading, services per component and etc.) but here having just one global injector would be perfectly fine. Ex. the Spring framework has one global injector. Why making the things complex when they can be simple (KISS).
Using the class references as tokens and symbols for custom tokens solve the issue of using string tokens and accidentally overriding components in the injector.

saskodh on 20 Oct 2017

👍1

Hi @kwtsangaf,
It's not possible to inject controller by another controller. Let's move your logic into the components.
@saskodh hierarchical injector exists to follow the idea of the domain encapsulation. Each module is some kind of facade and decides which component/service/anything might be used outside.

kamilmysliwiec on 21 Oct 2017

Thank you for all reply. Yup I miss understanding between controller and component. I thought I cannot call component directly but need to pass through controller instead. I am wrong.

kwtsangaf on 23 Oct 2017

For the structure design, basically,
component B only used in module A by now, it should be under module A.
But I want it able to be used by other modules in future
so I isolate component B into module B.
I don't know whether this approach is good or not.

kwtsangaf on 23 Oct 2017

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