CODEWITHSUNDEEP
javaandroidfirebasefirebase-realtime-database
zomnombom
zomnombom

Reputation: 994

Google firebase check if child exists

In my app, I need to check if a given element of my database on firebase has a child with a given name. I hoped it could be done by using something along the lines of:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();

if (rootRef.childExists("name")) {
    //run some code
}

I searched but I couldn't find anything useful.

Upvotes: 45

Views: 106413

Answers (6)

John T
John T

Reputation: 1082

A complete solution. No need to download all the data. Just check if the child exist like this:

// Assuming the names are in the name node. Remove "name/" if not
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference("name/" + name);
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {

    @Override
    public void onDataChange(DataSnapshot snapshot) {
         if (snapshot.exists()) {
             // Exist! Do whatever.

         } else {
             // Don't exist! Do something.

         }
    }

    @Override
    public void onCancelled(DatabaseError error) {
        // Failed, how to handle?

    }

});

Upvotes: 7

John yepthomi
John yepthomi

Reputation: 1

Use snapshot.exists() to check if the referenced database entry contains a child , irrespective of the value of the child.

Upvotes: 0

Arsen Nersisyan
Arsen Nersisyan

Reputation: 468

Don't do like this

NEVER

It will take all your data and bring to device

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  void onDataChange(DataSnapshot snapshot) {
    if (snapshot.hasChild("name")) {
      // run some code
    }
  }
});

Check it by this way. It will return the value of the child if exists, otherwise -> null

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.child("childName")
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  void onDataChange(DataSnapshot snapshot) {
    if (snapshot.getValue() == null) {
      // The child doesn't exist
    }
  }
});

Upvotes: 11

Arjun
Arjun

Reputation: 1599

UsersRef = FirebaseDatabase.getInstance().getReference();   
Users.addListenerForSingleValueEvent(new ValueEventListener() {
                                @Override
                                public void onDataChange(DataSnapshot snapshot) {
                                    if (snapshot.hasChild("childName")) {

                                        // it exists!
                                    }else{
                                       // does not exist
                                    }
                                }

                                @Override
                                public void onCancelled(@NonNull DatabaseError databaseError) {

                                }
                            });

Upvotes: 0

Thomas Bouldin
Thomas Bouldin

Reputation: 3725

Edit 2; worth putting on top: I think it is worth mentioning that this is actually downloading all data at this snapshot just to check whether any data exists. You should be mindful here. If the reference is huge (e.g. actually the root reference and not a specific child/property) then you should either find a deeper node you can use to check for existence or design your data structure differently so an efficient check is possible.

A database reference is effectively the URL for that data. You want to actually get data to see whether a child exists. This is why the method you seem to be looking for is on DataSnapshot.

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  void onDataChange(DataSnapshot snapshot) {
    if (snapshot.hasChild("name")) {
      // run some code
    }
  }
});

Now, this design pattern feels a bit strange. You're reading the whole database just to see whether "name" exists. You can make this a bit more efficient by listening to rootRef.child("name") and then just checking whether snapshot.exists().

If you're trying to do validation here, and not control flow, you should consider putting this code in your rules.json.

edit: I originally used the wrong function name (childExists instead of hasChild)

Upvotes: 87

Rahul Shah
Rahul Shah

Reputation: 1407

Try using .childexists in combination with .equalTo("Your specific name")

Upvotes: 2

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