Provide ContactService via a module

apps/parent-form/src/app/app.component.spec.ts

@@ -5,11 +5,12 @@ import { AppComponent } from './app.component';
 import { RouterTestingModule } from '@angular/router/testing';
 import { ReactiveFormsModule } from '@angular/forms';
 import { NameComponent } from './name/name.component';
+import { ContactModule } from '@nested-forms/contact';
 
 describe('AppComponent', () => {
   beforeEach(async(() => {
     TestBed.configureTestingModule({
-      imports: [RouterTestingModule, ReactiveFormsModule],
+      imports: [RouterTestingModule, ReactiveFormsModule, ContactModule.forRoot()],
       declarations: [AppComponent, NameComponent, AddressListComponent, AddressComponent]
     }).compileComponents();
   }));

apps/parent-form/src/app/app.component.ts

@@ -1,5 +1,4 @@
-import { ContactService } from './../../../../libs/contact/src/lib/contact.service';
-import { Contact } from '@nested-forms/contact';
+import { Contact, ContactService } from '@nested-forms/contact';
 import { Component, OnInit, OnDestroy } from '@angular/core';
 import { FormGroup, FormBuilder } from '@angular/forms';
 import { Subscription } from 'rxjs';

apps/parent-form/src/app/app.module.ts

@@ -7,6 +7,7 @@ import { ReactiveFormsModule } from '@angular/forms';
 import { NameComponent } from './name/name.component';
 import { AddressListComponent } from './address-list/address-list.component';
 import { AddressComponent } from './address/address.component';
+import { ContactModule } from '@nested-forms/contact';
 
 @NgModule({
   declarations: [AppComponent, NameComponent, AddressListComponent, AddressComponent],
@@ -14,6 +15,7 @@ import { AddressComponent } from './address/address.component';
     BrowserModule,
     RouterModule.forRoot([], { initialNavigation: 'enabled' }),
     ReactiveFormsModule,
+    ContactModule.forRoot(),
   ],
   providers: [],
   bootstrap: [AppComponent]

libs/contact/src/index.ts

@@ -1,2 +1,3 @@
 export * from './lib/contact-model';
 export * from './lib/contact.service';
+export * from './lib/contact.module';

libs/contact/src/lib/contact.module.ts

@@ -0,0 +1,28 @@
+import { NgModule, Optional, SkipSelf } from '@angular/core';
+import { CommonModule } from '@angular/common';
+import { ContactService } from './contact.service';
+
+@NgModule({
+  declarations: [],
+  imports: [
+    CommonModule
+  ]
+})
+export class ContactModule { 
+  constructor(
+    @Optional()
+    @SkipSelf()
+    parentModule: ContactModule
+  ) {
+    if (parentModule) {
+      throw new Error('ContactModule is already loaded. Import it in the AppModule only');
+    }
+  }
+
+  static forRoot() {
+    return {
+      ngModule: ContactModule,
+      providers: [ ContactService ]
+    }
+  }
+}

libs/contact/src/lib/contact.service.ts

@@ -27,9 +27,7 @@ const contact: Contact = {
   ],
 };
 
-@Injectable({
-  providedIn: 'root'
-})
+@Injectable()
 export class ContactService {
   constructor() { }