How to get the Object key of the associated object in angularFire2?

Question

I query the database by userkey to find if an associated object exists:

let url = ``/userMember/${userKey}``;

const userMemberRef = this.af.database.object(url, { preserveSnapshot: true });

userMemberRef.subscribe(data => {
  if(data.val()!=null) {
    console.log(data.val());
    memberKey= data.val();
  }
});
return memberKey;

It logs this in console which is good because the data I want is there.

Object {-Ke2CyV2BJ5S3_7qcQj5: true}

But how can I return the child key value "-Ke2CyV2BJ5S3_7qcQj5"?

Seems to be very trivial. I appreciate your help!

Here, the `subscribe` is asynchronous, so you are returning `memberKey` before it has a value assigned. See http://stackoverflow.com/a/6847754/6680611 — cartant, Mar 04 '17 at 23:27
So what is the solution to get the value? I thought the subscribe will unwrap it. I need the value unwrap as it is needed by the consuming method. — alltej, Mar 05 '17 at 06:38

score 1 · Answer 1 · answered Mar 05 '17 at 08:48

data.val() actually references the value of userKey. Since userMember/${userKey} is not a path to a key value pair but an object, the "value" of userKey is that object. If you want to assign the key of a property of that object to a variable, you will need to map to the property's key.

Since it's safe to assume you can't predict what that key will be, there isn't a straightforward way to do this as far as I know. On the plus side there are a number of conceivable ways to do this. The important thing is that you understand the above.

The fact that you don't have a straightforward way to access this key and want to might be an indication that you should reconsider the structure of your model if at all possible.

I'll leave you with this example of how to "get at" the key, mostly to illustrate its relationship to the path you're using:

this.af.database.object(`userMember/${userKey}`)
.subscribe(member => console.log(Object.keys(member)[0]));

the syntax that works for me is `console.log(Object.keys(member.val())[0]);` — alltej, Mar 07 '17 at 05:39
I assume because you're using `preserveSnapshot`. Did you try to log the keys without it? — J. Adam Connor, Mar 07 '17 at 06:32

score 1 · Answer 2 · answered May 07 '17 at 13:24

1

just use

const key = object['$key'];

answered May 07 '17 at 13:24

Sifeng

713
9
23

BANG! you a boss :D this is imho the most elegant solution – Unispaw Aug 28 '17 at 15:22

How to get the Object key of the associated object in angularFire2?

2 Answers2