Resolve cyclic dependency caused by utilizing the useFactory parameter

Question

Resolve cyclic dependency caused by utilizing the useFactory parameter

I am working with an injectable service that utilizes the useFactory attribute to determine whether it should be injected or if an implemented type should be used instead.

import { Injectable } from '@angular/core';
import { Router } from '@angular/router';
import { signatureConfigurationServiceFactory } from '../../environments/services.factories';
import { RestService } from '.';

@Injectable({
  providedIn: 'root',
  useFactory: signatureConfigurationServiceFactory,
  deps: [Router, RestService]
})
export class SignatureConfigurationService {

  constructor(public router: Router, public restService: RestService) {
  }

  // ... 
}

The factory function is located in a separate file named services.factories.ts. I have set it up this way so that I can easily swap it out using fileReplacements during the ng build process with another similar file containing a different factory function.

import { Router } from '@angular/router';
import { RestService } from '../app/services';
import { SignatureConfigurationService } from '../app/services/signature-configuration.service';

export let signatureConfigurationServiceFactory = (router: Router, restService: RestService) => {
  return new SignatureConfigurationService(router, restService);
};

However, I am encountering a circular reference issue since my service references the factory and vice versa.

While the Angular documentation suggests using forwardRef to resolve such issues, the examples provided did not seem applicable to my scenario.

What is the best approach to break out of this circular dependency while still keeping the factory method in a separate file?

angular typescript

Answer 1

Answer №1

I managed to find a solution.

As part of my approach, I introduced a new class named ServiceFactoriesRegistry. This class houses all the factory functions as static properties of a type that is a function returning any, eliminating the need to import the service file directly.

import { Router } from '@angular/router';
import { RestService } from '.';

export class ServiceFactoriesRegistry {
  public static signatureConfigurationServiceFactory: (router: Router, restService: RestService) => any;
}

To implement this, I modified the existing file containing the factory function to assign the factory method to this newly created registry. The file, named services.factories.ts, which will be swapped out at build time, depends on both the factory method and the service itself.

import { Router } from '@angular/router';
import { RestService } from '../app/services';
import { ServiceFactoriesRegistry } from '../app/services/service-registry';
import { SignatureConfigurationService } from '../app/services/signature-configuration.service';

export function registerServices() {
  ServiceFactoriesRegistry.signatureConfigurationServiceFactory = (router: Router, restService: RestService) => {
    return new SignatureConfigurationService(router, restService);
  };
}

This registration function is called within my AppModule:

export class AppModule {
  constructor() {
    registerServices();
  }
}

Within the service, I make use of the factory registry. While there is a dependency on the registry itself, there isn't a direct dependency on the service factory method since it's registered externally.

@Injectable({
  providedIn: 'root',
  useFactory: ServiceFactoriesRegistry.signatureConfigurationServiceFactory,
  deps: [Router, RestService]
})
export class SignatureConfigurationService

Answer 2

I managed to find a solution.

As part of my approach, I introduced a new class named ServiceFactoriesRegistry. This class houses all the factory functions as static properties of a type that is a function returning any, eliminating the need to import the service file directly.

import { Router } from '@angular/router';
import { RestService } from '.';

export class ServiceFactoriesRegistry {
  public static signatureConfigurationServiceFactory: (router: Router, restService: RestService) => any;
}

To implement this, I modified the existing file containing the factory function to assign the factory method to this newly created registry. The file, named services.factories.ts, which will be swapped out at build time, depends on both the factory method and the service itself.

import { Router } from '@angular/router';
import { RestService } from '../app/services';
import { ServiceFactoriesRegistry } from '../app/services/service-registry';
import { SignatureConfigurationService } from '../app/services/signature-configuration.service';

export function registerServices() {
  ServiceFactoriesRegistry.signatureConfigurationServiceFactory = (router: Router, restService: RestService) => {
    return new SignatureConfigurationService(router, restService);
  };
}

This registration function is called within my AppModule:

export class AppModule {
  constructor() {
    registerServices();
  }
}

Within the service, I make use of the factory registry. While there is a dependency on the registry itself, there isn't a direct dependency on the service factory method since it's registered externally.

@Injectable({
  providedIn: 'root',
  useFactory: ServiceFactoriesRegistry.signatureConfigurationServiceFactory,
  deps: [Router, RestService]
})
export class SignatureConfigurationService

Answer 3

Answer №2

When injecting variables in the constructor, there is no need to declare them separately. Declaring them in both places is redundant.

Instead of:

export class SignatureConfigurationService {
router: Router;
restService: RestService;

constructor(router: Router, restService: RestService) {
this.router = router;
this.restService = restService;
}

You can simplify it to:

export class SignatureConfigurationService {

  constructor(private router: Router,private restService: RestService) {}

Answer 4

When injecting variables in the constructor, there is no need to declare them separately. Declaring them in both places is redundant.

Instead of:

export class SignatureConfigurationService {
router: Router;
restService: RestService;

constructor(router: Router, restService: RestService) {
this.router = router;
this.restService = restService;
}

You can simplify it to:

export class SignatureConfigurationService {

  constructor(private router: Router,private restService: RestService) {}

Resolve cyclic dependency caused by utilizing the useFactory parameter

Answer №1

Answer №2

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