Firebase Database check if it's null value, doesn't work with DataSnapshot

Question

so I have a database where I search for products by barcodes.

I wanted to have a check to see if the products are in my database

mFirebaseInstance = FirebaseDatabase.getInstance();
mFirebaseDatabase = mFirebaseInstance.getReference("ProductData");
productId = mFirebaseDatabase.push().getKey();

public void searchProduct(String barcode){

    Query barcodeQuery = mFirebaseDatabase.child("Products")
            .orderByChild("barcode").equalTo(barcode);

    ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for(DataSnapshot ds : dataSnapshot.getChildren()) {

                    String name = ds.child("name").getValue(String.class);
                    int price = ds.child("price").getValue(Integer.class);
                    int quantity = ds.child("quantity").getValue(Integer.class);
                    Log.d("DATABASE", name + "/" + price + "/" + quantity);  /// The output that I get is this: Neopraxam/25/1    and  Vazelina/250/1

That's how I search for the products by barcode.

searchProduct("123123123");

searchProduct("3232");

I have tried to add these methods to check if the value I'm trying to get is null:

if (ds.exists()){}  OR
if (ds.getChildrenCount() != 0){}

But I have seen that it doesn't even enter in the loop if the value doesn't exist. So I'm assuming that It's coming from the query. So, how can I check if the query returns a null value because I used the method .equalTo(barcode) so I suppose that it should return a true or a false value

Hello, no, I haven't. So I guess that's how I should check if it's null or not ? @AliAhsan — Adrian, Apr 08 '20 at 22:44
@AliAhsan as long as the requested products are showing how they should I assume that I don't get any errors because I have checked and it doesn't even get into the DataSnapshot loop — Adrian, Apr 08 '20 at 22:48
@AliAhsan and I have searched for barcodes that doesn't exist but as I said, It doesn't even enter the DataSnapshot product. I use the query only there — Adrian, Apr 08 '20 at 22:58

Ali Ahsan · Answer 1 · 2020-04-08T23:21:07.007

1

Issue seem to be with onDataChange signature as it contains NonNull annotation. To execute onDataChange body even for DataSnapshot null value , update the signature as follows

   ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
        .
        .
        .

        }

Note: You should be using SingleValueEventListener instead of ValueEventListener

edited Apr 08 '20 at 23:21

answered Apr 08 '20 at 22:59

Ali Ahsan

985
11
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Actually, I have that in my code but I forgotten to put it. As I said, it's working as expected but the problem is that I could not find if the query is null or not – Adrian Apr 08 '20 at 23:02
Well you've `@NonNull` annotation. So when snapShot is null, body will not be executed – Ali Ahsan Apr 08 '20 at 23:10
Oh. So if I remove that, I’ll parse even null values. That’s good. Thanks – Adrian Apr 08 '20 at 23:12
np updating the answer. – Ali Ahsan Apr 08 '20 at 23:14

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

There is no way in which DataSnapshot's getChildren() method can return null:

Returns

True if the snapshot contains a non-null value, otherwise false

What you should use to solve the issue, is DataSnapshot's exists() method:

Returns

True if the snapshot contains a non-null value, otherwise false

So every time you perform a Query, check each item for existence using the above exists() method.

Besides that, your searchProduct() method can never return a value from the database. For more information, please see my answer from the following posT:

How to return DataSnapshot value as a result of a method?

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 09 '20 at 10:03

Alex Mamo

130,605
17
163
193

Thank you. I already solved. I removed the @nonull anotation and I checked dataSnapshot.exist() above the loop because I was checking ds.exist() inside the loop which was bad because there was no ds if there was no DataSnapshot to get childrens from – Adrian Apr 09 '20 at 10:06

Firebase Database check if it's null value, doesn't work with DataSnapshot

2 Answers2