nestjs singleton module instance dependency

nestjs-singleton-module-instance-dependency.md

The trick is:

• do not import/export/provide the DataService from ANY module (including app.module)
• just import the ConsumingService from app.module

---

DataService implements onModuleInit
    fetch countries, docTypes, etc
DataModule:
    providers: [DataService],
    exports: [DataService]

---

FirstConsumerService
    constructor(private readonly dependency: DataService) { }
FirstConsumerModule
    imports: [DataModule],
    providers: [FirstConsumerService]

---

AppModule
    imports: [FirstConsumerModule]

From: https://stackoverflow.com/questions/60192912/how-to-create-a-service-that-acts-as-a-singleton-with-nestjs