Ensure data is only loaded if not already loaded (needed to keep client/server state consistent)

samples/react/MusicStore/ReactApp/store/AlbumDetails.ts

@@ -7,12 +7,12 @@ import { Genre } from './GenreList';
 // STATE - This defines the type of data maintained in the Redux store.
 
 export interface AlbumDetailsState {
-    isLoaded: boolean;
     album: AlbumDetails;
+    requestedAlbumId: number;
 }
 
 export interface AlbumDetails {
-    AlbumId: string;
+    AlbumId: number;
     Title: string;
     AlbumArtUrl: string;
     Genre: Genre;
@@ -49,23 +49,31 @@ class ReceiveAlbumDetails extends Action {
 
 export const actionCreators = {    
     requestAlbumDetails: (albumId: number): ActionCreator => (dispatch, getState) => {
-        fetch(`/api/albums/${ albumId }`)
-            .then(results => results.json())
-            .then(album => dispatch(new ReceiveAlbumDetails(album)));
-        
-        dispatch(new RequestAlbumDetails(albumId));
+        // Only load if it's not already loaded (or currently being loaded)
+        if (albumId !== getState().albumDetails.requestedAlbumId) {
+            fetch(`/api/albums/${ albumId }`)
+                .then(results => results.json())
+                .then(album => {
+                    // Only replace state if it's still the most recent request
+                    if (albumId === getState().albumDetails.requestedAlbumId) {
+                        dispatch(new ReceiveAlbumDetails(album));
+                    }
+                });
+            
+            dispatch(new RequestAlbumDetails(albumId));
+        }
     }
 };
 
 // ----------------
 // REDUCER - For a given state and action, returns the new state. To support time travel, this must not mutate the old state.
 // For unrecognized actions, must return the existing state (or default initial state if none was supplied).
-const unloadedState: AlbumDetailsState = { isLoaded: false, album: null };
+const unloadedState: AlbumDetailsState = { requestedAlbumId: null as number, album: null };
 export const reducer: Reducer<AlbumDetailsState> = (state, action) => {
     if (isActionType(action, RequestAlbumDetails)) {
-        return unloadedState;
+        return { requestedAlbumId: action.albumId, album: null };
     } else if (isActionType(action, ReceiveAlbumDetails)) {
-        return { isLoaded: true, album: action.album };
+        return { requestedAlbumId: action.album.AlbumId, album: action.album };
     } else {
         return state || unloadedState;
     }

samples/react/MusicStore/ReactApp/store/FeaturedAlbums.ts

@@ -7,6 +7,7 @@ import { ActionCreator } from './';
 
 export interface FeaturedAlbumsState {
     albums: Album[];
+    isLoaded: boolean;
 }
 
 export interface Album {
@@ -37,11 +38,13 @@ class ReceiveFeaturedAlbums extends Action {
 
 export const actionCreators = {
     requestFeaturedAlbums: (): ActionCreator => (dispatch, getState) => {
-        fetch('/api/albums/mostPopular')
-            .then(results => results.json())
-            .then(albums => dispatch(new ReceiveFeaturedAlbums(albums)));
-        
-        return dispatch(new RequestFeaturedAlbums());        
+        if (!getState().featuredAlbums.isLoaded) {
+            fetch('/api/albums/mostPopular')
+                .then(results => results.json())
+                .then(albums => dispatch(new ReceiveFeaturedAlbums(albums)));
+            
+            return dispatch(new RequestFeaturedAlbums());
+        }
     }
 };
 
@@ -51,8 +54,8 @@ export const actionCreators = {
 
 export const reducer: Reducer<FeaturedAlbumsState> = (state, action) => {
     if (isActionType(action, ReceiveFeaturedAlbums)) {
-        return { albums: action.albums };
+        return { albums: action.albums, isLoaded: true };
     } else {
-        return state || { albums: [] };
+        return state || { albums: [], isLoaded: false };
     }
 };

samples/react/MusicStore/ReactApp/store/GenreDetails.ts

@@ -7,8 +7,9 @@ import { Album } from './FeaturedAlbums';
 // STATE - This defines the type of data maintained in the Redux store.
 
 export interface GenreDetailsState {
-    isLoaded: boolean;
+    requestedGenreId: number;
     albums: Album[];
+    isLoaded: boolean;
 }
 
 // -----------------
@@ -25,7 +26,7 @@ class RequestGenreDetails extends Action {
 
 @typeName("RECEIVE_GENRE_DETAILS")
 class ReceiveGenreDetails extends Action {
-    constructor(public albums: Album[]) {
+    constructor(public genreId: number, public albums: Album[]) {
         super();
     }
 }
@@ -36,24 +37,31 @@ class ReceiveGenreDetails extends Action {
 
 export const actionCreators = {    
     requestGenreDetails: (genreId: number): ActionCreator => (dispatch, getState) => {
-        fetch(`/api/genres/${ genreId }/albums`)
-            .then(results => results.json())
-            .then(albums => dispatch(new ReceiveGenreDetails(albums)));
-        
-        dispatch(new RequestGenreDetails(genreId));
+        // Only load if it's not already loaded (or currently being loaded)
+        if (genreId !== getState().genreDetails.requestedGenreId) {
+            fetch(`/api/genres/${ genreId }/albums`)
+                .then(results => results.json())
+                .then(albums => {
+                    // Only replace state if it's still the most recent request
+                    if (genreId === getState().genreDetails.requestedGenreId) {
+                        dispatch(new ReceiveGenreDetails(genreId, albums)); 
+                    }
+                });
+            
+            dispatch(new RequestGenreDetails(genreId));
+        }
     }
 };
 
 // ----------------
 // REDUCER - For a given state and action, returns the new state. To support time travel, this must not mutate the old state.
 // For unrecognized actions, must return the existing state (or default initial state if none was supplied).
-const unloadedState: GenreDetailsState = { isLoaded: false, albums: [] };
 export const reducer: Reducer<GenreDetailsState> = (state, action) => {
     if (isActionType(action, RequestGenreDetails)) {
-        return unloadedState;
+        return { requestedGenreId: action.genreId, albums: [], isLoaded: false };
     } else if (isActionType(action, ReceiveGenreDetails)) {
-        return { isLoaded: true, albums: action.albums };
+        return { requestedGenreId: action.genreId, albums: action.albums, isLoaded: true };
     } else {
-        return state || unloadedState;
+        return state || { requestedGenreId: null as number, albums: [], isLoaded: false };
     }
 };

samples/react/MusicStore/ReactApp/store/GenreList.ts

@@ -7,6 +7,7 @@ import { ActionCreator } from './';
 
 export interface GenresListState {
     genres: Genre[];
+    isLoaded: boolean;
 }
 
 export interface Genre {
@@ -32,9 +33,11 @@ class ReceiveGenresList extends Action {
 
 export const actionCreators = {    
     requestGenresList: (): ActionCreator => (dispatch, getState) => {
-        fetch('/api/genres')
-            .then(results => results.json())
-            .then(genres => dispatch(new ReceiveGenresList(genres)));
+        if (!getState().genreList.isLoaded) {
+            fetch('/api/genres')
+                .then(results => results.json())
+                .then(genres => dispatch(new ReceiveGenresList(genres)));
+        }
     }
 };
 
@@ -44,8 +47,8 @@ export const actionCreators = {
 
 export const reducer: Reducer<GenresListState> = (state, action) => {
     if (isActionType(action, ReceiveGenresList)) {
-        return { genres: action.genres };
+        return { genres: action.genres, isLoaded: true };
     } else {
-        return state || { genres: [] };
+        return state || { genres: [], isLoaded: false };
     }
 };