NgRx Store-根據另一個狀態對象的屬性有條件地加載數據

Question

我有一個應用程序，可以根據季節ID從我的API呈現燈具，結果等-該ID作為SeasonState的屬性存儲在狀態中：

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

其他組件使用它來確定要從API中獲取並存儲狀態的燈具，結果等。 例如：

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

這很好，但是我真正想要的是只能再次獲取固定裝置，該特定季節的固定裝置尚未存儲在狀態中。

我嘗試創建一個選擇器以有條件地從我的效果中從API加載數據：

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

但是我不確定如何實施此方法/這是否是正確的方法。

編輯：使用來自以下答案的信息，我編寫了以下效果，但是請參見注釋-我需要能夠使用withLatestFrom中有效負載中的seasonId。

@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

像這樣設置效果[我正在使用ngrx 6，因此已在ngrx 6上進行了測試； 如果您使用的是其他版本，那么您將有所了解並相應地調整代碼]-

@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()];
                                                    }
                                                   )
                                               )
                                }
                            })
                        );
          })
      )

現在，您需要分派從服務/組件或應用程序的設計中獲取指定seasonId固定裝置的操作。

希望它能給您一個想法並幫助您解決問題。