javascript - 如果有效负载长度 < 1，则返回不同的可观察值

Question

我有这个史诗:

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))
        )
    })

我只想返回

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

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

尝试:

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))
        )
    })

出现错误:

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

如何返回Observable.of上面，并返回一个可观察的 showAlertDialog如果action.payload.products.length < 1 。

Answer 1

mergeMap 中的普通条件怎么样？

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()
        );
      }
    })

<小时/>

顺便说一句，您的 catch 目前是无关紧要的，因为 Observable.of 永远不会抛出错误:

.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)
  ))
})