Querying a child node based on another attribute in firebase realtime database problem

Question

My data in firebase looks like below:

/users
  --key1
    --cards
       --card1
         --name: X
         --age: 40
       --card2
         --name Y
         --age  45 
    --email: [email protected]

the code to query data looks like below

  this.userCardList = this.db.list<Card>('users', ref => ref.orderByChild('email').equalTo(email))

    return this.userCardList.snapshotChanges().pipe(
       map(changes => 
        changes.map(c => ({ key: c.payload.key, ...c.payload.val()}))
       )
      ) ;

i am invoking in my component.ts as below

 ngOnInit() {
    this.cards =   this.dataSvc.fetchUserCards(this.core.email).pipe(
      map((cards: any) => cards.map(cardObj => {
            var c = new Card(cardObj.key)

                  c.firstName = cardObj._firstName
                  c.lastName = cardObj._lastName
                  c.jobTitle = cardObj._jobTitle

                return c
        }))
    );
  }

The problem is that the above code is not mapped to cards node rather key1 node. if replace it as users/cards that does not work either.

My expectation is to be able to get cards node data rather the parent node.

So what is the actual output and what is the desired output? — AVJT82
– AVJT82, Commented Aug 30, 2019 at 11:45
i have updated the question to respond to your both questions — Moblize IT
– Moblize IT, Commented Aug 30, 2019 at 14:33
I want the cards node. So how should it look like? Do you mean cards = [{card1: {...}}, {card2: {...}}]? — AVJT82
– AVJT82, Commented Aug 30, 2019 at 17:06

AVJT82 · Accepted Answer · 2019-08-31 10:59:46Z

Okay in the comment I asked about the output, but realized now that the example I presented isn't valid. All cards should be wrapped inside an object if you would want an array. And it wouldn't really make sense to have one object of objects inside an array, So instead of an array with one item, you would get an object with all the cards, like so:

{ 
  "card1": {"name":"name1", ... },
  "card2": {"name":"name2", ... }
}

So first of all, you need to return the cards node that you want. Also you don't seem to want the key of the document(s) returned as per my comment, so let's omit that and only return the cards:

map(changes => 
  changes.map(c => ({ ...c.payload.val().cards }))
)

Then, just if in case you get more than one object listed from the query, let's apply all to a singe object:

this.cards = this.dataSvc.fetchUserCards(this.core.email).pipe(
  map(cards => return Object.assign.apply(null, cards))
);

This will give your desired output at the top of my answer.

Moblize IT · Accepted Answer · 2019-08-31 15:32:03Z

so i decided to do it little differently. Now, i am doing it in 2 steps. First I am getting the key using the email as

 return new Promise((resolve, reject) => {
                  this.db.list("/users", ref => ref.orderByChild('email').equalTo(email)).snapshotChanges().pipe(
                    map(changes => 
                     changes.map(c => ({ key: c.payload.key, ...c.payload.val()}))
                    )
                   ).subscribe(
                    (res:any) => {
                        resolve(res)
                    },
                    err => {
                        console.log(err)
                        reject(err)
                    }
                  )}
                )

and then from the key i am fetching the cards array i need as below

 this.userCardList = this.db.list<Card>('users/' + key + '/cards', ref => ref.orderByChild('_status').equalTo(GlobalVariables.SYNCED))

    return this.userCardList.snapshotChanges().pipe(
       map(changes => 
        changes.map(c => ({ key: c.payload.key, ...c.payload.val()}))
       )
      ) ;

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