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为了减少网络流量，我需要检查具有给定 id 的实体是否在商店中，如果没有，则应从服务器请求它。我找不到任何配置，所以我只是使用 RxJs 对逻辑进行硬编码，如下所示。

有没有办法用 NgRx/NgRx 数据配置它？有没有一种方法可以配置实体在商店中的停留时间而不需要重新请求？

import {
  EntityCollectionServiceBase,
  EntityCollectionServiceElementsFactory,
} from '@ngrx/data';
import { Injectable } from '@angular/core';

import { MyEntity } from 'app/state/my-entity/MyEntity';
import { Observable, of, Subject } from 'rxjs';
import { distinct, filter, switchMap, tap } from 'rxjs/operators';

@Injectable({
  providedIn: 'root',
})
export class MyEntityDataService extends EntityCollectionServiceBase<MyEntity> {

  private id$ = new Subject<string|number>();

  constructor(serviceElementsFactory: EntityCollectionServiceElementsFactory) {
    super('MyEntity', serviceElementsFactory);

    // Fetching the data if not yet there
    this.id$.pipe(
      // Preventing multiple requests e.g. when multiple components
      // are requesting the same data
      distinct(),
      switchMap(
        (id: string|number): Observable<MyEntity | undefined> => this.filteredEntities$.pipe(
          switchMap(
            (entityCollection: MyEntity[]): Observable<MyEntity | undefined> => {

              const thatEntity: MyEntity | undefined =
                entityCollection.find((entity: MyEntity) => `${entity.id}` === `${id}`);

              return of(thatEntity).pipe(
                filter((v: MyEntity | undefined): boolean => !v),
                tap(() => super.getByKey(id))
              )
            }
          ),
        ),
      ),
    ).subscribe();
  }

  getByKey(id: string|number): Observable<MyEntity> {

    this.id$.next(id);

    return this.filteredEntities$.pipe(
      switchMap(
        (entityCollection: MyEntity[]) : Observable<MyEntity> => {
          const thatEntity: MyEntity | undefined = entityCollection.find(
            (entity: MyEntity) => `${entity.id}` === `${id}`
          );
          return thatEntity ? of(thatEntity) : of();
        }
      ),
    );
  }
}
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1 回答 1

1

我遇到了同样的问题，对我来说最好的解决方案是在发送操作之前检查效果。

//selectIdExists:selector recieve ID and return true if loaded or false if not found
//user should dispatch initialFindById and the effect will decide either to dispatch findById or no dispatching

initialFindById$ = createEffect(() => this.actions$.pipe(
        ofType(actions.initialFindById),
        mergeMap(action => this.store.select(selectors.selectIdExists(action.id))
            .pipe(
                filter(found => found == false),//Id not found 
                map(() => actions.findById({ id: action.id })),
            ))
    ));

如果您想确保即使商店中有数据也能获取数据，只需发送findbyId操作即可

于 2021-07-13T18:51:25.093 回答