NGRX Store-根据另一个状态对象的属性有条件加载数据

Question

我有一个基于季节ID的API的固定固定，结果等的应用程序 - 该ID作为季节的属性存储在状态下：

export interface SeasonsState extends EntityState<Season> {
  allSeasonsLoaded: boolean;
  currentlySelectedSeasonId: number;
}

其他组件使用这来确定哪些固定装置，结果等从API中获取并在状态下存储。例如：

this.store
    .pipe(
        select(selectCurrentlySelectedSeason)
    ).subscribe(seasonId => {
  this.store.dispatch(new AllFixturesBySeasonRequested({seasonId}));
  this.fixtures$ = this.store
      .pipe(
          select(selectAllFixturesFromSeason(seasonId))
      );
});

这效果很好，但是我真正想要的是只能在该特定季节再次获取固定装置。

我已经尝试创建一个选择器来使用我的效果中的API加载数据：

export const selectSeasonsLoaded = (seasonId: any) => createSelector(
    selectFixturesState,
    fixturesState => fixturesState.seasonsLoaded.find(seasonId)
);

，但我不确定如何实现此问题/这是否是正确的方法。

编辑：使用以下答案中的信息，我写了以下效果，但是请参阅评论 - 我需要能够在我的withlatest上使用有效载荷中的selesion ID。

。

@Effect()
loadFixturesBySeason$ = this.actions$
  .pipe(
      ofType<AllFixturesBySeasonRequested>(FixtureActionTypes.AllFixturesBySeasonRequested),
      withLatestFrom(this.store.select(selectAllFixtures)), // needs to be bySeasonId
      switchMap(([action, fixtures]) => {
          if (fixtures.length) {
              return [];
          }
          return this.fixtureService.getFixturesBySeason(action.payload.seasonId);
      }),
      map(fixtures => new AllFixturesBySeasonLoaded({fixtures}))
  );

Answer 1

具有这样的效果设置[我正在使用NGRX 6，因此在NGRX 6上进行了测试；如果您使用的是其他版本，那么您将获得一个想法并相应地调整代码] -

@Effect() allFixturesBySeasonRequested: Observable<Action> =
  this._actions$
      .pipe(
          //Please use your action here;
          ofType(actions.AllFixturesBySeasonRequested),
          //please adjust your action payload here as per your code
          //bottom line is to map your dispatched action to the action's payload
          map(action => action.payload ),
          switchMap(seasonId => {
              //first get the fixtures for the seasonId from the store
              //check its value if there are fixtures for the specified seasonId
              //then dont fetch it from the server; If NO fixtures then fetch the same from the server
              return this.store
                        .pipe(
                            select(selectAllFixturesFromSeason(seasonId)),
                            //this will ensure not to trigger this again when you update the fixtures in your store after fetching from the backend.
                            take(1),
                            mergeMap(fixtures => {
                                //check here if fixtures has something OR have your logic to know
                                //if fixtures are there
                                //I am assuming it is an array
                                if (fixtures && fixtures.lenght) {
                                    //here you can either return NO action or return an action
                                    //which informs that fixtures already there
                                    //or send action as per your app logic
                                    return [];
                                } else {
                                    //NO fixtures in the store for seasonId; get it from there server
                                    return this.http.get(/*your URL to get the fixtures from the backend*/)=
                                               .pipe(
                                                   mergeMap(res => {
                                                        return [new YourFixtureFetchedSucccess()];
                                                    }
                                                   )
                                               )
                                }
                            })
                        );
          })
      )

现在，您需要派遣从您的服务/组件或应用程序设计方式获取指定季节的固定装置的操作。

希望它能给您一个想法并有助于解决您的问题。