refactor followlinks to use a single object for all params and add an isOptional param. Also add support for embedding links to search service

src/app/+bitstream-page/bitstream-page.resolver.ts

@@ -35,7 +35,7 @@ export class BitstreamPageResolver implements Resolve<RemoteData<Bitstream>> {
      */
     get followLinks(): FollowLinkConfig<Bitstream>[] {
         return [
-            followLink('bundle', undefined, true, true, true, followLink('item')),
+            followLink('bundle', {}, followLink('item')),
             followLink('format')
         ];
     }

src/app/+collection-page/collection-page.resolver.ts

@@ -14,7 +14,7 @@ import { ResolvedAction } from '../core/resolving/resolver.actions';
  * Requesting them as embeds will limit the number of requests
  */
 export const COLLECTION_PAGE_LINKS_TO_FOLLOW: FollowLinkConfig<Collection>[] = [
-  followLink('parentCommunity', undefined, true, true, true,
+  followLink('parentCommunity', {},
     followLink('parentCommunity')
   ),
   followLink('logo')

src/app/+item-page/edit-item-page/item-authorizations/item-authorizations.component.ts

@@ -79,7 +79,7 @@ export class ItemAuthorizationsComponent implements OnInit, OnDestroy {
       getFirstSucceededRemoteDataWithNotEmptyPayload(),
       map((item: Item) => this.linkService.resolveLink(
         item,
-        followLink('bundles', new FindListOptions(), true, true, true, followLink('bitstreams'))
+        followLink('bundles', {}, followLink('bitstreams'))
       ))
     ) as Observable<Item>;
 

src/app/+item-page/edit-item-page/item-relationships/edit-relationship-list/edit-relationship-list.component.ts

@@ -323,7 +323,7 @@ export class EditRelationshipListComponent implements OnInit {
 
   private getItemRelationships() {
     this.linkService.resolveLink(this.item,
-      followLink('relationships', undefined, true, true, true,
+      followLink('relationships', {},
         followLink('relationshipType'),
         followLink('leftItem'),
         followLink('rightItem'),

src/app/+item-page/item.resolver.ts

@@ -15,13 +15,13 @@ import { ResolvedAction } from '../core/resolving/resolver.actions';
  * Requesting them as embeds will limit the number of requests
  */
 export const ITEM_PAGE_LINKS_TO_FOLLOW: FollowLinkConfig<Item>[] = [
-  followLink('owningCollection', undefined, true, true, true,
+  followLink('owningCollection', {},
-    followLink('parentCommunity', undefined, true, true, true,
+    followLink('parentCommunity', {},
       followLink('parentCommunity'))
   ),
-  followLink('bundles', new FindListOptions(), true, true, true, followLink('bitstreams')),
+  followLink('bundles', {}, followLink('bitstreams')),
   followLink('relationships'),
-  followLink('version', undefined, true, true, true, followLink('versionhistory')),
+  followLink('version', {}, followLink('versionhistory')),
 ];
 
 /**

src/app/+search-page/search.component.ts

@@ -16,9 +16,11 @@ import { SearchResult } from '../shared/search/search-result.model';
 import { SearchConfigurationService } from '../core/shared/search/search-configuration.service';
 import { SearchService } from '../core/shared/search/search.service';
 import { currentPath } from '../shared/utils/route.utils';
-import { Router} from '@angular/router';
+import { Router } from '@angular/router';
 import { Context } from '../core/shared/context.model';
 import { SortOptions } from '../core/cache/models/sort-options.model';
+import { followLink } from '../shared/utils/follow-link-config.model';
+import { Item } from '../core/shared/item.model';
 
 @Component({
   selector: 'ds-search',

src/app/community-list-page/community-list-service.ts

@@ -174,8 +174,8 @@ export class CommunityListService {
           direction: options.sort.direction
         }
       },
-      followLink('subcommunities', this.configOnePage, true, true),
+      followLink('subcommunities', { findListOptions: this.configOnePage }),
-      followLink('collections', this.configOnePage, true, true))
+      followLink('collections', { findListOptions: this.configOnePage }))
       .pipe(
         getFirstSucceededRemoteData(),
         map((results) => results.payload),
@@ -242,8 +242,8 @@ export class CommunityListService {
             elementsPerPage: MAX_COMCOLS_PER_PAGE,
             currentPage: i
           },
-          followLink('subcommunities', this.configOnePage, true, true),
+          followLink('subcommunities', { findListOptions: this.configOnePage }),
-          followLink('collections', this.configOnePage, true, true))
+          followLink('collections', { findListOptions: this.configOnePage }))
           .pipe(
             getFirstCompletedRemoteData(),
             switchMap((rd: RemoteData<PaginatedList<Community>>) => {

src/app/core/cache/builders/link.service.spec.ts

@@ -102,7 +102,7 @@ describe('LinkService', () => {
   describe('resolveLink', () => {
     describe(`when the linkdefinition concerns a single object`, () => {
       beforeEach(() => {
-        service.resolveLink(testModel, followLink('predecessor', {}, true, true, true, followLink('successor')));
+        service.resolveLink(testModel, followLink('predecessor', {}, followLink('successor')));
       });
       it('should call dataservice.findByHref with the correct href and nested links', () => {
         expect(testDataService.findByHref).toHaveBeenCalledWith(testModel._links.predecessor.href, true, true, followLink('successor'));
@@ -116,7 +116,7 @@ describe('LinkService', () => {
           propertyName: 'predecessor',
           isList: true
         });
-        service.resolveLink(testModel, followLink('predecessor', { some: 'options ' } as any, true, true, true, followLink('successor')));
+        service.resolveLink(testModel, followLink('predecessor', { findListOptions: { some: 'options ' } as any }, followLink('successor')));
       });
       it('should call dataservice.findAllByHref with the correct href, findListOptions,  and nested links', () => {
         expect(testDataService.findAllByHref).toHaveBeenCalledWith(testModel._links.predecessor.href, { some: 'options ' } as any, true, true, followLink('successor'));
@@ -124,7 +124,7 @@ describe('LinkService', () => {
     });
     describe('either way', () => {
       beforeEach(() => {
-        result = service.resolveLink(testModel, followLink('predecessor', {}, true, true, true, followLink('successor')));
+        result = service.resolveLink(testModel, followLink('predecessor', {}, followLink('successor')));
       });
 
       it('should call getLinkDefinition with the correct model and link', () => {
@@ -149,7 +149,7 @@ describe('LinkService', () => {
       });
       it('should throw an error', () => {
         expect(() => {
-          service.resolveLink(testModel, followLink('predecessor', {}, true, true, true, followLink('successor')));
+          service.resolveLink(testModel, followLink('predecessor', {}, followLink('successor')));
         }).toThrow();
       });
     });
@@ -160,7 +160,7 @@ describe('LinkService', () => {
       });
       it('should throw an error', () => {
         expect(() => {
-          service.resolveLink(testModel, followLink('predecessor', {}, true, true, true, followLink('successor')));
+          service.resolveLink(testModel, followLink('predecessor', {}, followLink('successor')));
         }).toThrow();
       });
     });

src/app/core/cache/builders/link.service.ts

@@ -55,9 +55,7 @@ export class LinkService {
   public resolveLinkWithoutAttaching<T extends HALResource, U extends HALResource>(model, linkToFollow: FollowLinkConfig<T>): Observable<RemoteData<U>> {
     const matchingLinkDef = this.getLinkDefinition(model.constructor, linkToFollow.name);
 
-    if (hasNoValue(matchingLinkDef)) {
+    if (hasValue(matchingLinkDef)) {
-      throw new Error(`followLink('${linkToFollow.name}') was used for a ${model.constructor.name}, but there is no property on ${model.constructor.name} models with an @link() for ${linkToFollow.name}`);
-    } else {
       const provider = this.getDataServiceFor(matchingLinkDef.resourceType);
 
       if (hasNoValue(provider)) {
@@ -84,7 +82,10 @@ export class LinkService {
           throw e;
         }
       }
+    } else if (!linkToFollow.isOptional) {
+      throw new Error(`followLink('${linkToFollow.name}') was used as a required link for a ${model.constructor.name}, but there is no property on ${model.constructor.name} models with an @link() for ${linkToFollow.name}`);
     }
+
     return EMPTY;
   }
 

src/app/core/cache/builders/remote-data-build.service.spec.ts

@@ -523,7 +523,7 @@ describe('RemoteDataBuildService', () => {
       let paginatedLinksToFollow;
       beforeEach(() => {
         paginatedLinksToFollow = [
-          followLink('page', undefined, true, true, true, ...linksToFollow),
+          followLink('page', {}, ...linksToFollow),
           ...linksToFollow
         ];
       });

src/app/core/cache/builders/remote-data-build.service.ts

@@ -271,7 +271,7 @@ export class RemoteDataBuildService {
    * @param linksToFollow     List of {@link FollowLinkConfig} that indicate which {@link HALLink}s should be automatically resolved
    */
   buildList<T extends HALResource>(href$: string | Observable<string>, ...linksToFollow: FollowLinkConfig<T>[]): Observable<RemoteData<PaginatedList<T>>> {
-    return this.buildFromHref<PaginatedList<T>>(href$, followLink('page', undefined, false, true, true, ...linksToFollow));
+    return this.buildFromHref<PaginatedList<T>>(href$, followLink('page', { shouldEmbed: false }, ...linksToFollow));
   }
 
   /**

src/app/core/data/data.service.spec.ts

@@ -233,7 +233,7 @@ describe('DataService', () => {
       const config: FindListOptions = Object.assign(new FindListOptions(), {
         elementsPerPage: 5
       });
-      (service as any).getFindAllHref({}, null, followLink('bundles', config,  true, true, true)).subscribe((value) => {
+      (service as any).getFindAllHref({}, null, followLink('bundles', { findListOptions: config })).subscribe((value) => {
         expect(value).toBe(expected);
       });
     });
@@ -253,7 +253,7 @@ describe('DataService', () => {
         elementsPerPage: 2
       });
 
-      (service as any).getFindAllHref({}, null, followLink('bundles'), followLink('owningCollection', config, true, true, true), followLink('templateItemOf')).subscribe((value) => {
+      (service as any).getFindAllHref({}, null, followLink('bundles'), followLink('owningCollection', { findListOptions: config }), followLink('templateItemOf')).subscribe((value) => {
         expect(value).toBe(expected);
       });
     });
@@ -261,7 +261,13 @@ describe('DataService', () => {
     it('should not include linksToFollow with shouldEmbed = false', () => {
       const expected = `${endpoint}?embed=templateItemOf`;
 
-      (service as any).getFindAllHref({}, null, followLink('bundles', undefined, false), followLink('owningCollection', undefined, false), followLink('templateItemOf')).subscribe((value) => {
+      (service as any).getFindAllHref(
+        {},
+        null,
+        followLink('bundles', { shouldEmbed: false }),
+        followLink('owningCollection', { shouldEmbed: false }),
+        followLink('templateItemOf')
+      ).subscribe((value) => {
         expect(value).toBe(expected);
       });
     });
@@ -269,7 +275,7 @@ describe('DataService', () => {
     it('should include nested linksToFollow 3lvl', () => {
       const expected = `${endpoint}?embed=owningCollection/itemtemplate/relationships`;
 
-      (service as any).getFindAllHref({}, null, followLink('owningCollection', undefined, true, true, true, followLink('itemtemplate', undefined, true, true, true, followLink('relationships')))).subscribe((value) => {
+      (service as any).getFindAllHref({}, null, followLink('owningCollection', {}, followLink('itemtemplate', {}, followLink('relationships')))).subscribe((value) => {
         expect(value).toBe(expected);
       });
     });
@@ -279,7 +285,7 @@ describe('DataService', () => {
       const config: FindListOptions = Object.assign(new FindListOptions(), {
         elementsPerPage: 4
       });
-      (service as any).getFindAllHref({}, null, followLink('owningCollection', undefined, true, true, true, followLink('itemtemplate', config, true, true, true))).subscribe((value) => {
+      (service as any).getFindAllHref({}, null, followLink('owningCollection', {}, followLink('itemtemplate', { findListOptions: config }))).subscribe((value) => {
         expect(value).toBe(expected);
       });
     });
@@ -308,13 +314,19 @@ describe('DataService', () => {
 
     it('should not include linksToFollow with shouldEmbed = false', () => {
       const expected = `${endpointMock}/${resourceIdMock}?embed=templateItemOf`;
-      const result = (service as any).getIDHref(endpointMock, resourceIdMock, followLink('bundles', undefined, false), followLink('owningCollection', undefined, false), followLink('templateItemOf'));
+      const result = (service as any).getIDHref(
+        endpointMock,
+        resourceIdMock,
+        followLink('bundles', { shouldEmbed: false }),
+        followLink('owningCollection', { shouldEmbed: false }),
+        followLink('templateItemOf')
+      );
       expect(result).toEqual(expected);
     });
 
     it('should include nested linksToFollow 3lvl', () => {
       const expected = `${endpointMock}/${resourceIdMock}?embed=owningCollection/itemtemplate/relationships`;
-      const result = (service as any).getIDHref(endpointMock, resourceIdMock, followLink('owningCollection', undefined, true,  true, true,followLink('itemtemplate', undefined, true, true, true, followLink('relationships'))));
+      const result = (service as any).getIDHref(endpointMock, resourceIdMock, followLink('owningCollection', {}, followLink('itemtemplate', {}, followLink('relationships'))));
       expect(result).toEqual(expected);
     });
   });

src/app/core/data/dso-redirect-data.service.spec.ts

@@ -174,13 +174,29 @@ describe('DsoRedirectDataService', () => {
 
     it('should not include linksToFollow with shouldEmbed = false', () => {
       const expected = `${requestUUIDURL}&embed=templateItemOf`;
-      const result = (service as any).getIDHref(pidLink, dsoUUID, followLink('bundles', undefined, false), followLink('owningCollection', undefined, false), followLink('templateItemOf'));
+      const result = (service as any).getIDHref(
+        pidLink,
+        dsoUUID,
+        followLink('bundles', { shouldEmbed: false }),
+        followLink('owningCollection', { shouldEmbed: false }),
+        followLink('templateItemOf')
+      );
       expect(result).toEqual(expected);
     });
 
     it('should include nested linksToFollow 3lvl', () => {
       const expected = `${requestUUIDURL}&embed=owningCollection/itemtemplate/relationships`;
-      const result = (service as any).getIDHref(pidLink, dsoUUID, followLink('owningCollection', undefined, true, true, true, followLink('itemtemplate', undefined, true, true, true, followLink('relationships'))));
+      const result = (service as any).getIDHref(
+        pidLink,
+        dsoUUID,
+        followLink('owningCollection',
+          {},
+          followLink('itemtemplate',
+            {},
+            followLink('relationships')
+          )
+        )
+      );
       expect(result).toEqual(expected);
     });
   });

src/app/core/shared/search/search.service.ts

@@ -41,6 +41,43 @@ import { SearchConfig } from './search-filters/search-config.model';
 import { PaginationService } from '../../pagination/pagination.service';
 import { SearchConfigurationService } from './search-configuration.service';
 import { PaginationComponentOptions } from '../../../shared/pagination/pagination-component-options.model';
+import { DataService } from '../../data/data.service';
+import { Store } from '@ngrx/store';
+import { CoreState } from '../../core.reducers';
+import { ObjectCacheService } from '../../cache/object-cache.service';
+import { NotificationsService } from '../../../shared/notifications/notifications.service';
+import { HttpClient } from '@angular/common/http';
+import { DSOChangeAnalyzer } from '../../data/dso-change-analyzer.service';
+
+/* tslint:disable:max-classes-per-file */
+/**
+ * A class that lets us delegate some methods to DataService
+ */
+class DataServiceImpl extends DataService<any> {
+  protected linkPath = 'discover';
+
+  constructor(
+    protected requestService: RequestService,
+    protected rdbService: RemoteDataBuildService,
+    protected store: Store<CoreState>,
+    protected objectCache: ObjectCacheService,
+    protected halService: HALEndpointService,
+    protected notificationsService: NotificationsService,
+    protected http: HttpClient,
+    protected comparator: DSOChangeAnalyzer<any>) {
+    super();
+  }
+
+  /**
+   * Adds the embed options to the link for the request
+   * @param href            The href the params are to be added to
+   * @param args            params for the query string
+   * @param linksToFollow   links we want to embed in query string if shouldEmbed is true
+   */
+  public addEmbedParams(href: string, args: string[], ...linksToFollow: FollowLinkConfig<any>[]) {
+    return super.addEmbedParams(href, args, ...linksToFollow);
+  }
+}
 
 /**
  * Service that performs all general actions that have to do with the search page
@@ -78,6 +115,11 @@ export class SearchService implements OnDestroy {
    */
   private sub;
 
+  /**
+   * Instance of DataServiceImpl that lets us delegate some methods to DataService
+   */
+  private searchDataService: DataServiceImpl;
+
   constructor(private router: Router,
               private routeService: RouteService,
               protected requestService: RequestService,
@@ -89,6 +131,16 @@ export class SearchService implements OnDestroy {
               private paginationService: PaginationService,
               private searchConfigurationService: SearchConfigurationService
   ) {
+    this.searchDataService = new DataServiceImpl(
+      undefined,
+      undefined,
+      undefined,
+      undefined,
+      undefined,
+      undefined,
+      undefined,
+      undefined
+    );
   }
 
   /**
@@ -131,7 +183,17 @@ export class SearchService implements OnDestroy {
   search<T extends DSpaceObject>(searchOptions?: PaginatedSearchOptions, responseMsToLive?: number, useCachedVersionIfAvailable = true, reRequestOnStale = true, ...linksToFollow: FollowLinkConfig<T>[]): Observable<RemoteData<SearchObjects<T>>> {
     const href$ = this.getEndpoint(searchOptions);
 
-    href$.pipe(take(1)).subscribe((url: string) => {
+    href$.pipe(
+      take(1),
+      map((href: string) => {
+        const args = this.searchDataService.addEmbedParams(href, [], ...linksToFollow);
+        if (isNotEmpty(args)) {
+          return new URLCombiner(href, `?${args.join('&')}`).toString();
+        } else {
+          return href;
+        }
+      })
+    ).subscribe((url: string) => {
       const request = new this.request(this.requestService.generateRequestId(), url);
 
       const getResponseParserFn: () => GenericConstructor<ResponseParsingService> = () => {
@@ -399,9 +461,9 @@ export class SearchService implements OnDestroy {
         let pageParams = { page: 1 };
         const queryParams = { view: viewMode };
         if (viewMode === ViewMode.DetailedListElement) {
-          pageParams = Object.assign(pageParams, {pageSize: 1});
+          pageParams = Object.assign(pageParams, { pageSize: 1 });
         } else if (config.pageSize === 1) {
-          pageParams = Object.assign(pageParams, {pageSize: 10});
+          pageParams = Object.assign(pageParams, { pageSize: 10 });
         }
         this.paginationService.updateRouteWithUrl(this.searchConfigurationService.paginationID, hasValue(searchLinkParts) ? searchLinkParts : [this.getSearchLink()], pageParams, queryParams);
       });
@@ -413,7 +475,7 @@ export class SearchService implements OnDestroy {
    * @param {string} configurationName the name of the configuration
    * @returns {Observable<RemoteData<SearchConfig[]>>} The found configuration
    */
-  getSearchConfigurationFor(scope?: string, configurationName?: string ): Observable<RemoteData<SearchConfig>> {
+  getSearchConfigurationFor(scope?: string, configurationName?: string): Observable<RemoteData<SearchConfig>> {
     const href$ = this.halService.getEndpoint(this.configurationLinkPath).pipe(
       map((url: string) => this.getConfigUrl(url, scope, configurationName)),
     );

src/app/core/submission/vocabularies/vocabulary.service.ts

@@ -173,7 +173,7 @@ export class VocabularyService {
     );
 
     // TODO remove false for the entries embed when https://github.com/DSpace/DSpace/issues/3096 is solved
-    return this.findVocabularyById(vocabularyOptions.name, true, true, followLink('entries', options,  false)).pipe(
+    return this.findVocabularyById(vocabularyOptions.name, true, true, followLink('entries', { findListOptions: options, shouldEmbed: false })).pipe(
       getFirstSucceededRemoteDataPayload(),
       switchMap((vocabulary: Vocabulary) => vocabulary.entries),
     );
@@ -200,7 +200,7 @@ export class VocabularyService {
     );
 
     // TODO remove false for the entries embed when https://github.com/DSpace/DSpace/issues/3096 is solved
-    return this.findVocabularyById(vocabularyOptions.name, true, true, followLink('entries', options, false)).pipe(
+    return this.findVocabularyById(vocabularyOptions.name, true, true, followLink('entries', { findListOptions: options, shouldEmbed: false })).pipe(
       getFirstSucceededRemoteDataPayload(),
       switchMap((vocabulary: Vocabulary) => vocabulary.entries),
     );
@@ -249,7 +249,7 @@ export class VocabularyService {
     );
 
     // TODO remove false for the entries embed when https://github.com/DSpace/DSpace/issues/3096 is solved
-    return this.findVocabularyById(vocabularyOptions.name, true, true, followLink('entries', options, false)).pipe(
+    return this.findVocabularyById(vocabularyOptions.name, true, true, followLink('entries', { findListOptions: options, shouldEmbed: false })).pipe(
       getFirstSucceededRemoteDataPayload(),
       switchMap((vocabulary: Vocabulary) => vocabulary.entries),
       getFirstSucceededRemoteListPayload(),

src/app/shared/object-detail/my-dspace-result-detail-element/claimed-task-search-result/claimed-task-search-result-detail-element.component.ts

@@ -49,8 +49,8 @@ export class ClaimedTaskSearchResultDetailElementComponent extends SearchResultD
    */
   ngOnInit() {
     super.ngOnInit();
-    this.linkService.resolveLinks(this.dso, followLink('workflowitem', null, true, true, true,
+    this.linkService.resolveLinks(this.dso, followLink('workflowitem', {},
-      followLink('item', null, true, true, true, followLink('bundles')),
+      followLink('item', {}, followLink('bundles')),
       followLink('submitter')
     ), followLink('action'));
     this.workflowitemRD$ = this.dso.workflowitem as Observable<RemoteData<WorkflowItem>>;

src/app/shared/object-detail/my-dspace-result-detail-element/pool-search-result/pool-search-result-detail-element.component.ts

@@ -48,8 +48,8 @@ export class PoolSearchResultDetailElementComponent extends SearchResultDetailEl
    */
   ngOnInit() {
     super.ngOnInit();
-    this.linkService.resolveLinks(this.dso, followLink('workflowitem', null, true, true, true,
+    this.linkService.resolveLinks(this.dso, followLink('workflowitem', {},
-      followLink('item', null, true, true, true, followLink('bundles')),
+      followLink('item', {}, followLink('bundles')),
       followLink('submitter')
     ), followLink('action'));
     this.workflowitemRD$ = this.dso.workflowitem as Observable<RemoteData<WorkflowItem>>;

src/app/shared/object-list/my-dspace-result-list-element/claimed-search-result/claimed-approved-search-result/claimed-approved-search-result-list-element.component.ts

@@ -55,10 +55,7 @@ export class ClaimedApprovedSearchResultListElementComponent extends SearchResul
     super.ngOnInit();
     this.linkService.resolveLinks(this.dso,
       followLink('workflowitem',
-        null,
+        { useCachedVersionIfAvailable: false },
-        true,
-        false,
-        true,
         followLink('item'),
         followLink('submitter')
       ),

src/app/shared/object-list/my-dspace-result-list-element/claimed-search-result/claimed-declined-search-result/claimed-declined-search-result-list-element.component.ts

@@ -56,10 +56,7 @@ export class ClaimedDeclinedSearchResultListElementComponent extends SearchResul
     super.ngOnInit();
     this.linkService.resolveLinks(this.dso,
       followLink('workflowitem',
-        null,
+        { useCachedVersionIfAvailable: false },
-        true,
-        false,
-        true,
         followLink('item'),
         followLink('submitter')
       ),

src/app/shared/object-list/my-dspace-result-list-element/claimed-search-result/claimed-search-result-list-element.component.ts

@@ -50,7 +50,7 @@ export class ClaimedSearchResultListElementComponent extends SearchResultListEle
    */
   ngOnInit() {
     super.ngOnInit();
-    this.linkService.resolveLinks(this.dso, followLink('workflowitem', null, true, true, true,
+    this.linkService.resolveLinks(this.dso, followLink('workflowitem', {},
       followLink('item'), followLink('submitter')
     ), followLink('action'));
     this.workflowitemRD$ = this.dso.workflowitem as Observable<RemoteData<WorkflowItem>>;

src/app/shared/object-list/my-dspace-result-list-element/pool-search-result/pool-search-result-list-element.component.ts

@@ -60,7 +60,7 @@ export class PoolSearchResultListElementComponent extends SearchResultListElemen
    */
   ngOnInit() {
     super.ngOnInit();
-    this.linkService.resolveLinks(this.dso, followLink('workflowitem', null, true, true, true,
+    this.linkService.resolveLinks(this.dso, followLink('workflowitem', {},
       followLink('item'), followLink('submitter')
     ), followLink('action'));
     this.workflowitemRD$ = this.dso.workflowitem as Observable<RemoteData<WorkflowItem>>;

src/app/shared/utils/follow-link-config.model.ts

@@ -1,5 +1,6 @@
 import { FindListOptions } from '../../core/data/request.models';
 import { HALResource } from '../../core/shared/hal-resource.model';
+import { hasValue } from '../empty.util';
 
 /**
  * A class to send the retrieval of a {@link HALLink}
@@ -40,6 +41,12 @@ export class FollowLinkConfig<R extends HALResource> {
    * Defaults to true
    */
   reRequestOnStale? = true;
+
+  /**
+   * If this is false an error will be thrown if the link doesn't exist on the model it is used on
+   * Defaults to false
+   */
+  isOptional? = false;
 }
 
 /**
@@ -57,23 +64,35 @@ export class FollowLinkConfig<R extends HALResource> {
  * no valid cached version. Defaults
  * @param reRequestOnStale: Whether or not the link should automatically be re-requested after the
  * response becomes stale
+ * @param isOptional: Whether or not to fail if the link doesn't exist
  * @param linksToFollow: a list of {@link FollowLinkConfig}s to
  * use on the retrieved object.
  */
 export const followLink = <R extends HALResource>(
   linkName: keyof R['_links'],
-  findListOptions?: FindListOptions,
+  {
-  shouldEmbed = true,
-  useCachedVersionIfAvailable = true,
-  reRequestOnStale = true,
-  ...linksToFollow: FollowLinkConfig<any>[]
-): FollowLinkConfig<R> => {
-  return {
-    name: linkName,
     findListOptions,
     shouldEmbed,
     useCachedVersionIfAvailable,
     reRequestOnStale,
+    isOptional
+  }: {
+    findListOptions?: FindListOptions,
+    shouldEmbed?: boolean,
+    useCachedVersionIfAvailable?: boolean,
+    reRequestOnStale?: boolean,
+    isOptional?: boolean,
+  } = {},
+  ...linksToFollow: FollowLinkConfig<any>[]
+): FollowLinkConfig<R> => {
+  const followLinkConfig = {
+    name: linkName,
+    findListOptions: hasValue(findListOptions) ? findListOptions : new FindListOptions(),
+    shouldEmbed: hasValue(shouldEmbed) ? shouldEmbed : true,
+    useCachedVersionIfAvailable: hasValue(useCachedVersionIfAvailable) ? useCachedVersionIfAvailable : true,
+    reRequestOnStale: hasValue(reRequestOnStale) ? reRequestOnStale : true,
+    isOptional: hasValue(isOptional) ? isOptional : false,
     linksToFollow
   };
+  return followLinkConfig;
 };