使用Angular2，angularfire2和Typescript从Firebase对象中获取数据

Question

Im currently working on a Project with Angular 2 and angularFire2. My database looks like this in Firebase: base:/data

[{Name:test1},
{Name:test2},
{Name:test3}]

All of the items also have the Firebase key.

Now im trying to get data out of the Firebase with the Observabels from RX. When i do this, i get the names in the Console:

let items= af.database.list('/data').map(i=>{return i});
items.forEach(i=>i.forEach(e=>(console.log(e.name))));

Output: test1,test2,test3. Everything Works.

But when i do this:

console.log(items.first());

I get a FirebaseListObservable back.

How can i get only the First Object from the FirebaseListObservable? How can i edit Items in the list? like:

items[0].name=test3

And How can i get the Firebase Key from an Item

how can i get The firebaseKey from an Item in the list?

Answer 1

Observables are an asynchronous data structure, meaning that you don't actually know when the data is going to be available, you have to subscribe to the Observable and wait for the data to become available in the next handler.

items.first().subscribe(x => console.log(x.name));

Further, an Observable is not static, so you can't index into it as such. If you need only the first item then I would suggest instead that you extract the value and modify it with a flatMap + first + map combination.

af.database.list('/data')
  //Convert array into Observable and flatten it
  .flatMap(list => list)
  //Get only the first item in this list
  .first()
  //Transform the value
  .map(({name, firebaseKey}) => ({name: "test3", firebaseKey}))
  //Subscribe to the stream
  .subscribe(x => console.log(x));