在 observable 中使用 observable 的角度

问题描述

我正在制作一个 angular 6 的费用管理器 web 应用程序.我的数据库在 firebase 上.我正在使用 angularfire2 lib 来检索和更新数据.

I am making an expense manager webapp with angular 6. My database is on firebase. I am using the angularfire2 lib to retrieve and update the data.

数据库设计如下

获取类别的函数是

getCategory(uid:String,categorykey:string):Observable<any>
   {

return this.afdb.object(`users/${uid}/categories/${categorykey}`)
  .snapshotChanges()
  .pipe(map(c=>({key:c.payload.key,...c.payload.val()})));}

返回带有费用数组的 observable 的函数是

the function that returns observable with an array of expenses is

getExpensesWithKeys(uid:String):Observable<any>{
return this.afdb.list(users/${uid}/expenses)
.snapshotChanges()
.pipe(
  map(changes =>
  changes.map(c =>
({key:c.payload.key,...c.payload.val()}))
  )
);
 }

在我的组件中，我可以得到我的费用

In my component I can get my expenses as

expenses:Expense[];
getExpensesWithKey("userid-123")
.subscribe(expenses=>this.expenses=expenses)

和任何类别

category:Category;
getCategory("userid-123",expenses[0].category)
.subscribe(category=>this.category=category);

我想创建一个 observable，它获取费用数组并返回每个费用的类别，我可以将其放入类别数组中.我一直在绞尽脑汁将这两个 observable 与各种 rxjs 操作符结合起来，但无济于事.

I want to create an observable that gets the expenses array and returns the category for each expense which i can push into an array of categories.I've been racking my brain to combine the two observables with all kinds of rxjs operaters but to no avail.

非常感谢您的帮助.

只是想添加一些我已经尝试过的方法.我尝试过的一种方法是

edit:Just wanted to add a few methods I tried already.One method I tried was

this.getExpensesWithKeys("user-123")
.pipe(mergeMap(expenses=>
expenses.map(expense=>
this.getCategory("user-123",expense.category)))).subscribe(console.log);

但它只是发出一个 Observable 数组.如何获取类别对象并将它们推送到数组中?

but it just emitting an array of Observables. How can i get the category objects and push them into an array?

我试过的另一种方法

this.rtdbService.getExpensesWithKeys("user-123")
.pipe(map(expenses=>
   expenses.map(expense=>expense.category)))
   .pipe(mergeMap(ids=>
this.rtdbService.getCategory("user-123",ids)))
.subscribe(console.log);

这只是发出类别的键.

我也尝试了下面提供的答案，但没有发出任何内容.

I also tried the below provided answer as well which is not emitting anything.

提前致谢

推荐答案

我终于找到了解决方案

  getExpensewithCategories(uid:String):Observable<any>{
    ;
    let expwithCat$=this.getExpenses(uid).pipe(mergeMap(expenses =>{
      return expenses.map(expense => this.getCategory(uid,expense.category)
      .pipe(map(cat=>
        ({expensekey:expense.key,
          amount:expense.amount,
          date:expense.date,
          expcatkey:expense.category,
          categorykey:cat.key,
          color:cat.color,
          name:cat.name})
        )
      ))
   }
    }));

      return expwithCat$.pipe(mergeAll())
}

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