107155: Allow caching null objects

src/app/core/cache/object-cache.reducer.ts

@@ -166,10 +166,12 @@ export function objectCacheReducer(state = initialState, action: ObjectCacheActi
  *    the new state, with the object added, or overwritten.
  */
 function addToObjectCache(state: ObjectCacheState, action: AddToObjectCacheAction): ObjectCacheState {
-  const existing = state[action.payload.objectToCache._links.self.href] || {} as any;
+  const cacheLink = hasValue(action.payload.objectToCache) ? action.payload.objectToCache._links.self.href : action.payload.alternativeLink;
+  const existing = state[cacheLink] || {} as any;
   const newAltLinks = hasValue(action.payload.alternativeLink) ? [action.payload.alternativeLink] : [];
+  if (hasValue(cacheLink)) {
     return Object.assign({}, state, {
-    [action.payload.objectToCache._links.self.href]: {
+      [cacheLink]: {
         data: action.payload.objectToCache,
         timeCompleted: action.payload.timeCompleted,
         msToLive: action.payload.msToLive,
@@ -180,6 +182,9 @@ function addToObjectCache(state: ObjectCacheState, action: AddToObjectCacheActio
         alternativeLinks: [...(existing.alternativeLinks || []), ...newAltLinks]
       } as ObjectCacheEntry
     });
+  } else {
+    return state;
+  }
 }
 
 /**

src/app/core/cache/object-cache.service.ts

@@ -63,7 +63,9 @@ export class ObjectCacheService {
    *    An optional alternative link to this object
    */
   add(object: CacheableObject, msToLive: number, requestUUID: string, alternativeLink?: string): void {
+    if (hasValue(object)) {
       object = this.linkService.removeResolvedLinks(object); // Ensure the object we're storing has no resolved links
+    }
     this.store.dispatch(new AddToObjectCacheAction(object, new Date().getTime(), msToLive, requestUUID, alternativeLink));
   }
 
@@ -139,11 +141,15 @@ export class ObjectCacheService {
         }
       ),
       map((entry: ObjectCacheEntry) => {
+        if (hasValue(entry.data)) {
           const type: GenericConstructor<T> = getClassForType((entry.data as any).type);
           if (typeof type !== 'function') {
             throw new Error(`${type} is not a valid constructor for ${JSON.stringify(entry.data)}`);
           }
           return Object.assign(new type(), entry.data) as T;
+        } else {
+          return null;
+        }
       })
     );
   }

src/app/core/data/dspace-rest-response-parsing.service.ts

@@ -109,6 +109,9 @@ export class DspaceRestResponseParsingService implements ResponseParsingService
               if (hasValue(match)) {
                 embedAltUrl = new URLCombiner(embedAltUrl, `?size=${match.size}`).toString();
               }
+              if (data._embedded[property] == null) {
+                this.addToObjectCache(null, request, data, embedAltUrl);
+              }
               this.process<ObjectDomain>(data._embedded[property], request, embedAltUrl);
             });
         }
@@ -226,7 +229,7 @@ export class DspaceRestResponseParsingService implements ResponseParsingService
    * @param alternativeURL  an alternative url that can be used to retrieve the object
    */
   addToObjectCache(co: CacheableObject, request: RestRequest, data: any, alternativeURL?: string): void {
-    if (!isCacheableObject(co)) {
+    if (hasValue(co) && !isCacheableObject(co)) {
       const type = hasValue(data) && hasValue(data.type) ? data.type : 'object';
       let dataJSON: string;
       if (hasValue(data._embedded)) {
@@ -240,7 +243,7 @@ export class DspaceRestResponseParsingService implements ResponseParsingService
       return;
     }
 
-    if (alternativeURL === co._links.self.href) {
+    if (hasValue(co) && alternativeURL === co._links.self.href) {
       alternativeURL = undefined;
     }
 

src/app/core/index/index.effects.ts

@@ -27,7 +27,7 @@ export class UUIDIndexEffects {
    addObject$ = createEffect(() => this.actions$
     .pipe(
       ofType(ObjectCacheActionTypes.ADD),
-      filter((action: AddToObjectCacheAction) => hasValue(action.payload.objectToCache.uuid)),
+      filter((action: AddToObjectCacheAction) => hasValue(action.payload.objectToCache) && hasValue(action.payload.objectToCache.uuid)),
       map((action: AddToObjectCacheAction) => {
         return new AddToIndexAction(
           IndexName.OBJECT,
@@ -46,7 +46,7 @@ export class UUIDIndexEffects {
       ofType(ObjectCacheActionTypes.ADD),
       map((action: AddToObjectCacheAction) => {
         const alternativeLink = action.payload.alternativeLink;
-        const selfLink = action.payload.objectToCache._links.self.href;
+        const selfLink = hasValue(action.payload.objectToCache) ? action.payload.objectToCache._links.self.href : alternativeLink;
         if (hasValue(alternativeLink) && alternativeLink !== selfLink) {
           return new AddToIndexAction(
             IndexName.ALTERNATIVE_OBJECT_LINK,