From b0aacf784480da585c71081a096222552c9b9b3e Mon Sep 17 00:00:00 2001
From: AdditionAddict <48436581+AdditionAddict@users.noreply.github.com>
Date: Wed, 11 Mar 2020 12:22:18 +0000
Subject: [PATCH] fix(example): optimistically add/remove book from collection
 (#2429)

Closes #2417
---
 .../app/books/reducers/collection.reducer.ts    | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/projects/example-app/src/app/books/reducers/collection.reducer.ts b/projects/example-app/src/app/books/reducers/collection.reducer.ts
index 7430c64247..2a87061d2a 100644
--- a/projects/example-app/src/app/books/reducers/collection.reducer.ts
+++ b/projects/example-app/src/app/books/reducers/collection.reducer.ts
@@ -3,6 +3,7 @@ import { createReducer, on } from '@ngrx/store';
 import {
   CollectionApiActions,
   CollectionPageActions,
+  SelectedBookPageActions,
 } from '@example-app/books/actions';
 
 export const collectionFeatureKey = 'collection';
@@ -30,9 +31,15 @@ export const reducer = createReducer(
     loading: false,
     ids: books.map(book => book.id),
   })),
-  // Supports handing multiple types of actions
+  /**
+   * Optimistically add book to collection.
+   * If this succeeds there's nothing to do.
+   * If this fails we revert state by removing the book.
+   *
+   * `on` supports handling multiple types of actions
+   */
   on(
-    CollectionApiActions.addBookSuccess,
+    SelectedBookPageActions.addBook,
     CollectionApiActions.removeBookFailure,
     (state, { book }) => {
       if (state.ids.indexOf(book.id) > -1) {
@@ -44,8 +51,12 @@ export const reducer = createReducer(
       };
     }
   ),
+  /**
+   * Optimistically remove book from collection.
+   * If addBook fails, we "undo" adding the book.
+   */
   on(
-    CollectionApiActions.removeBookSuccess,
+    SelectedBookPageActions.removeBook,
     CollectionApiActions.addBookFailure,
     (state, { book }) => ({
       ...state,