通过 pipe() 中的 switchMap() 展开可观察数组 return

Question

我有一个方法 getFolders() returns Observable。

function getFolders() {

  const data = [
       {
          name: "Photos",
          files: of(2) // observable
       },
       {
          name: "Document",
          files: of(5) // observable
       },
       {
          name: "Videos",
          files: of(2) // observable
       }
  ];

  return of(data);

}

我需要 总文件数 9 (2+5+2)。我写了一个函数来通过以下用法来完成这项工作，

getFileCount.subscribe( totalCount => console.log(totalCount) );

// expects to log 9

实施是，

function getFileCount() {

   return getFolders()
            .pipe(
               switchMap( folderData => folderData.map( data => data.files ) ),
               // Above switchMap returns [ Observable, Observable, Observable ]
               // Now I need to complete all Observable and get flatten result like [2,5,2]

               mergeAll(),
               // I though the mergeAll will resolve all Observables and return the value
               
               switchMap( countArray => {

                   // expecting all values in a single array [2,5,2]
                   // but it executes for each value like
                   // 2
                   // 5
                   // 2

                   console.log(countArray);

                   return countArray.reduce(function(a, b) { return a + b; }, 0);
               })
            );

}

Answer 1

使用forkJoin包裹observable数组并移除mergeAll()，它会执行里面的每一个observable

switchMap( folderData => forkJoin(folderData.map( data => data.files ) )),

通过 pipe() 中的 switchMap() 展开可观察数组 return

Flatten array of observables return by switchMap() in pipe()

javascript

rxjs