docs(migration): Update migration docs and add example of injecting r…

…educers (#100)

MIGRATION.md

@@ -2,13 +2,26 @@
 
 This guide covers the changes between the ngrx projects migrating from V1.x/2.x to V4.
 
+[@ngrx/core](#ngrxcore)  
 [@ngrx/store](#ngrxstore)  
 [@ngrx/effects](#ngrxeffects)  
 [@ngrx/router-store](#ngrxrouter-store)  
 [@ngrx/store-devtools](#ngrxstore-devtools)
 
 ## @ngrx/core
-@ngrx/core is no longer used, and can conflict with @ngrx/store. You should remove it from your project.
+@ngrx/core is no longer needed, and can conflict with @ngrx/store. You should remove it from your project.
+
+BEFORE:
+
+```ts
+import { compose } from '@ngrx/core/compose';
+```
+
+AFTER:
+
+```ts
+import { compose } from '@ngrx/store';
+```
 
 ## @ngrx/store
 
@@ -191,7 +204,7 @@ describe('My Effects', () => {
 
   it('should work', () => {
     actions = hot('--a-', { a: SomeAction, ... });
-    
+
     const expected = cold('--b', { b: AnotherAction });
 
     expect(effects.someSource$).toBeObservable(expected);

docs/store/README.md

@@ -118,7 +118,8 @@ export class MyAppComponent {
 - [Selectors](./selectors.md)
 - [State composition through feature modules](./api.md#feature-module-state-composition)
 - [Providing initial state](./api.md#initial-state)
-- [Reducer composition](./api.md#reducer-factory)
+- [Meta-Reducers](./api.md#meta-reducers)
+- [Injecting reducers](./api.md#injecting-reducers)
 
 ### Additional Material
 - [From Inactive to Reactive with ngrx](https://www.youtube.com/watch?v=cyaAhXHhxgk)

docs/store/api.md

@@ -43,7 +43,7 @@ export function getInitialState() {
 })
 ```
 
-## Reducer Factory
+## Meta Reducers
 
 @ngrx/store composes your map of reducers into a single reducer. Use the `metaReducers`
 configuration option to provide an array of meta-reducers that are composed from right to left.
@@ -91,3 +91,35 @@ import { reducers } from './reducers';
 })
 export class FeatureModule {}
 ```
+
+## Injecting Reducers
+
+To inject the root reducers into your application, use an `InjectionToken` and a `Provider` to register the reducers through dependency injection.
+
+```ts
+import { NgModule, InjectionToken } from '@angular/core';
+import { StoreModule, ActionReducerMap } from '@ngrx/store';
+
+import { SomeService } from './some.service';
+import * as fromRoot from './reducers';
+
+export const REDUCER_TOKEN = new InjectionToken<ActionReducerMap<fromRoot.State>>('Registered Reducers');
+
+export function getReducers(someService: SomeService) {
+  return someService.getReducers();
+}
+
+@NgModule({
+  imports: [
+    StoreModule.forRoot(REDUCER_TOKEN),
+  ],
+  providers: [
+    {
+      provide: REDUCER_TOKEN,
+      deps: [SomeService],
+      useFactory: getReducers
+    }
+  ]
+})
+export class AppModule { }
+```