How to get the key from the value in firebase

Question

How do I get the key "-KLpcURDV68BcbAvlPFy" when I know the field "name" contains "efg" in the following structure in Firebase.

clubs
    -KLpcURDV68BcbAvlPFy
        dept: "abc"
        desc: "xyz"
        name: "efg"
    -asdasdasddsad
        dept: "asda"
        desc: "asd"
        name: "adddd"

I tried this but it returned "clubs"

mDatabase.child("clubs").orderByChild("name").equalTo("efg").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            String clubkey =dataSnapshot.getKey();

score 23 · Accepted Answer · answered Jul 06 '16 at 19:29

That's because you're using a ValueEventListener. If the query matches multiple children, it returns a list of all those children. Even if there's only a single matches child, it's still a list of one. And since you're calling getKey() on that list, you get the key of the location where you ran the query.

To get the key of the matches children, loop over the children of the snapshot:

mDatabase.child("clubs")
         .orderByChild("name")
         .equalTo("efg")
         .addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
            String clubkey = childSnapshot.getKey();

But note that if you assume that the club name is unique, you might as well store the clubs under their name and access the correct one without a query:

mDatabase.child("clubs")
         .child("efg")
         .addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String clubkey = dataSnapshot.getKey(); // will be efg

score 6 · Answer 2 · answered Jul 22 '19 at 14:50

If anyone needs to do this using Kotlin:

mDatabase.child("clubs")
        .orderByChild("name")
        .equalTo("efg")
        .addListenerForSingleValueEvent(object: ValueEventListener {

            override fun onDataChange(dataSnapshot: DataSnapshot) {

                dataSnapshot.children.forEach {
                     //"it" is the snapshot
                     val key: String = it.key.toString()
                }
            }

            override fun onCancelled(p0: DatabaseError) {
                    //do whatever you need
            }
         })

score 3 · Answer 3 · edited Jan 01 '20 at 08:12

3

firebaseDatabase = FirebaseDatabase.getInstance();
mReference = firebaseDatabase.getReference("clubs");

mReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot ds: dataSnapshot.getChildren()){
            String key = ds.getKey();
        }
    }
｝

edited Jan 01 '20 at 08:12

recnac

3,744
6
24
46

answered Jan 01 '20 at 07:48

Malik Ali

175
5

score 2 · Answer 4 · edited Jan 31 '20 at 01:03

I've figured out a very easy way to do this. You need to get the auto-generated key before you send it to firebase. So for my project I did something like the following:

var database = firebase.database();
var rootRef = database.ref();
var autoId = rootRef.push().key
rootRef.child(autoId).set({
key: value,
key: value,
key: value,
autoid: autoId
})

Now when i go to my child added function and take a snapshot, I can easily get to snapshot.val().autoid and store it in a variable or as a button attribute so that I can delete it later.

score 0 · Answer 5 · answered Jun 06 '19 at 07:22

0

If this key (asdasdasddsad) also had the name:"efg" will club key will become asdasdasddsad and KLpcURDV68BcbAvlPFy

answered Jun 06 '19 at 07:22

Chirag Gupta

469
1
7
16

Above post should be a comment. – Abhishek Gurjar Jun 06 '19 at 07:51

score 0 · Answer 6 · answered Jan 01 '20 at 08:58

We can use HashMap.

initialize:

String for storing Key value. ModelClass for storing you data.

val hashMap: HashMap<String, "Your Model Class"> = hashMapOf()
databaseReference.child("/Product").orderByChild("ProductName")
        .addValueEventListener(object : ValueEventListener {
            override fun onCancelled(p0: DatabaseError) {

            }

            override fun onDataChange(p0: DataSnapshot) {
                /*p0.children.mapNotNullTo(models) { it.getValue(ProductModel::class.java) }.run {

                }*/
                p0.children.forEach {
                    val value = it.getValue(ProductModel::class.java) as ProductModel
                    hashMap[it.key!!] = value
                }.run { adp.update(hashMap) }
            }
        })

after this we can also get key & its value by using (index)

5 is Index

hashMap.keys.elementAt(5)
hashMap.values.elementAt(5)

score 0 · Answer 7 · answered Jun 08 '20 at 10:59

Here is how I did it in Kotlin

var ref  = database.child("clubs")
val database_listener = object : ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot) {
            for (ds in dataSnapshot.children) {
                val key = ds.key
           }
        }
     }
   ref.addValueEventListener(database_listener)

score 0 · Answer 8 · answered May 05 '22 at 22:38

Solution in Java (100% working!):

//firebase reference
DatabaseReference  mRef = FirebaseDatabase.getInstance().getReference();

//set THe_strOX's database contents from the question
mRef.child("clubs").child("-KLpcURDV68BcbAvlPFy").child("dept").setValue("abc");
mRef.child("clubs").child("-KLpcURDV68BcbAvlPFy").child("desc").setValue("xyz");
mRef.child("clubs").child("-KLpcURDV68BcbAvlPFy").child("name").setValue("efg");
mRef.child("clubs").child("-asdasdasddsad").child("dept").setValue("asda");
mRef.child("clubs").child("-asdasdasddsad").child("desc").setValue("asd");
mRef.child("clubs").child("-asdasdasddsad").child("name").setValue("adddd");
//

mRef.child("clubs").addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(@NonNull DataSnapshot dataSnapshot, String s)
    {
        if (dataSnapshot.exists())
        {
            String pushkey = dataSnapshot.getKey();
            mRef.child("clubs").child(pushkey).addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(@NonNull DataSnapshot dataSnapshot, String s)
                {
                    if (dataSnapshot.exists())
                    {
                        if (dataSnapshot.getKey().toString().equals("name")) {
                            //edit efg to any desired value
                            if (dataSnapshot.getValue().toString().equals("efg")) {
                                Toast.makeText(MainActivity.this, pushkey, Toast.LENGTH_SHORT).show();
                            }
                        }
                    }
                }
                @Override
                public void onChildChanged(@NonNull DataSnapshot dataSnapshot, String s) { }
                @Override
                public void onChildRemoved(@NonNull DataSnapshot snapshot) { }
                @Override
                public void onChildMoved(@NonNull DataSnapshot snapshot, @androidx.annotation.Nullable String previousChildName) { }
                @Override
                public void onCancelled(@NonNull DatabaseError error) { }
            });
        }
    }
    @Override
    public void onChildChanged(@NonNull DataSnapshot dataSnapshot, String s) { }
    @Override
    public void onChildRemoved(@NonNull DataSnapshot snapshot) { }
    @Override
    public void onChildMoved(@NonNull DataSnapshot snapshot, @androidx.annotation.Nullable String previousChildName) { }
    @Override
    public void onCancelled(@NonNull DatabaseError error) { }
});

}

How to get the key from the value in firebase

8 Answers8

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