返回不同可观察到的，如果有效载荷长度为<1

Question

我有这样的史诗：

export const fetchProductsFulfilledEpic = action$ => 
    action$.ofType(FETCH_PRODUCTS_FULFILLED) 
    .mergeMap(action => { 
     return Observable.of(
     updateSearchResults(action.payload), 
     toggleMenu(), 
     updateRegion(action.payload) 
    ).catch(error => Observable.of(
     fetchProductsRejected(error)) 
     ) 
    }) 

我想只返回

updateSearchResults(action.payload), 
toggleMenu(), 
updateRegion(action.payload) 

如果action.payload.products.length大于0，否则，显示警报。

Attmept：

export const fetchProductsFulfilledEpic = action$ => 
    action$.ofType(FETCH_PRODUCTS_FULFILLED) 
    .mergeMap(action => { 
     Observable.if(() => action.payload.products.length > 0, 
     Observable.of(
      updateSearchResults(action.payload), 
      toggleMenu(), 
      updateRegion(action.payload) 
     ), Observable.of(...enter alert observable here...) 
    ).catch(error => Observable.of(
     fetchProductsRejected(error)) 
     ) 
    }) 

收到错误：

You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.

如何退还上述Observable.of，并返回一个可观察与showAlertDialog如果action.payload.products.length < 1。

Answer 1

mergeMap内的正常条件如何？

export const fetchProductsFulfilledEpic = action$ => 
    action$.ofType(FETCH_PRODUCTS_FULFILLED) 
    .mergeMap(action => { 
     if (action.payload.products.length > 0) { 
     return Observable.of(
      updateSearchResults(action.payload), 
      toggleMenu(), 
      updateRegion(action.payload) 
     ); 
     } else { 
     return Observable.of(
      showAlertDialog() 
     ); 
     } 
    }) 

---

作为一个方面来看，你catch目前是多余的，因为一个Observable.of不会抛出错误：

.mergeMap(action => { 
    return Observable.of(
    updateSearchResults(action.payload), 
    toggleMenu(), 
    updateRegion(action.payload) 
    // this is catching errors on the above Observable but 
    // this Observable will never ever throw errors 
).catch(error => Observable.of(
    fetchProductsRejected(error) 
)) 
})