如何使用 JSON 中的数据初始化多个 nestjs 提供程序？

Question

I'm new to NestJS and am creating an application. My application utilizes the MVC architecture and has multiple modules for example

Project
 |
 +-- App.Controller
 +-- App.Service
 +-- App.Module
 |    
 +-- SubModule1
 |  |  
 |  +-- SubModule1.Controller
 |  +-- SubModule1.Service
 |  +-- SubModule1.Module
 |    
 +-- SubModule2
 |  |  
 |  +-- SubModule2.Controller
 |  +-- SubModule2.Service
 |  +-- SubModule2.Module
 |
 +-- SubModule3
 |  |  
 |  +-- SubModule3.Controller
 |  +-- SubModule3.Service
 |  +-- SubModule3.Module

Now each of my submodules service class has a data member

private member: string[] = []

I would like to initialise these class members with some data that i have stored in a json file. My json structure is as such

{
    'SubModule1' : [
        string1,
        string2,
        string3,
        ...
        stringN
    ], 
    'SubModule2' : [
        string1,
        string2,
        string3,
        ...
        stringN
    ], 
    'SubModule3' : [
        string1,
        string2,
        string3,
        ...
        stringN
    ]
}

Can anyone please guide me as to what is the right way to do this? Where should i load the json and then inject the data? My initial thoughts were to Utilize the app.service class to load and inject data, but i am unsure as to how can i access the submodule providers.

Any guidance or help will be much appreciated. Thank you

Answer 1

For initializing data during the start of your application, you can use one of the lifecycle events , for example OnModuleInit :

@Injectable()
export class MyService implements OnModuleInit {
  onModuleInit() {
    await initializeData()
  }
}

---

If you want to do that repeatedly for many provider of the same structure, you can extends from an initializer class like so:

abstract class DataInitializer implements OnModuleInit {
  member: string[];
  onModuleInit() {
    const jsonData = // ...
    this.member= jsonData[this.constructor.name];
  }
}

@Injectable()
export class AppService extends DataInitializer {
  // ...