RXjs groupBy - 组 AngularFire Firestore 集合 [英] RXjs groupBy - Group AngularFire Firestore collection

问题描述

我正在尝试按字段对 AngularFire Firestore 集合 (Observable[]) 进行分组，例如 userId.

我有一个项目集合，每个项目都有不同的 userId 值，我需要将它们分组到一个多维数组中.所以，转换..

<预><代码>[{用户ID:1，颜色:'蓝色'}，{userId:2, color:'green'},{用户 ID:1，颜色:'橙色'}]

进入

<预><代码>[[{用户ID:1，颜色:'蓝色'}，{用户 ID:1，颜色:'橙色'}],[{用户 ID:2，颜色:'绿色'}]]

我是 RxJs 的新手，我知道在制作 Observable.of(itemsArray) 时 groupBy 操作符是如何工作的，但我看不到如何让它与从 AgularFire

返回的 Observable 一起工作

let items:Observable[] = this.afs.collection('items').snapshotChanges().groupBy( item => item.userId );//item实际上是数组

它看起来像 AngularFire 返回一个 Observable，它作为一个整体发出 Array，而不是每个元素.

如果我map它，那么我是不是只有数组中的每个项目，而不能使用groupBy?

关于如何返回上述分组数组的 Observable 数组的任何指针?

解决方案

您可以简单地将数组的 observable 转换为数组值的 observable:

myObservable.flatMap(arr => Rx.Observable.from(arr));

I'm trying to group a AngularFire Firestore Collection (Observable[]) by a field, say userId.

I have a collection of items, each with varying userId values, and I need to group them into a multidimensional array. So, convert..

[ 
  {userID:1, color:'blue' }, 
  {userId:2, color:'green'}, 
  {userId:1, color:'orange'}
]

into

[ 
  [
   {userID:1, color:'blue' }, 
   {userId:1, color:'orange'}
  ],
  [
   {userId:2, color:'green'}
  ]
]

I'm totally new to RxJs, I get how the groupBy operator works when making an Observable.of(itemsArray), but I can't see how to get this to work with the Observable returned from AgularFire

let items:Observable[] = this.afs.collection<Item>('items')
  .snapshotChanges()
  .groupBy( item => item.userId ); //item is actually the array

It looks like AngularFire returns an Observable that emits the Array as a whole, not each element.

If I map it, dont I then just have each item in the array, and cant use the groupBy?

Any pointers on how to return a Observable array of grouped arrays as per above?

解决方案

You can simply turn your observable of array into an observable of the values of the array with:

myObservable.flatMap(arr => Rx.Observable.from(arr));

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