How to update entry in Firebase Database based on an attribute value

Question

I am using the Firebase Realtime Database with Android in Java. I have the following database screenshot:

I would like to change the availability value (from 0 to 1) for the ingredient with the attribute "ingredient_name = Lime". The attribute ingredient_name is actually something like a primary key meaning that there will be no other database entry with this specific name.

I tried the following code

DatabaseReference rootRef;
rootRef = FirebaseDatabase.getInstance("https://....app").getReference();
String ingredientToBeUpdate = "Lime";

rootRef.child("ingredients").orderByChild("ingredient_name").equalTo(ingredientToBeUpdate).child("availability").setValue(1);

But I get the error "Cannot resolve method 'child' in 'Query'". Can you tell me how to do this update properly? So I would like to update the value from the database entries who attribute "ingredient_name" is equal to a certain string ingredientToBeUpdate.

Answer 1

Firebase doesn't support so-called update queries, where you send a condition and the new data to the database and it them writes the new data for all nodes matching the condition.

Instead you will need to execute the query in your application code, loop through the results, and update each of them in turn:

rootRef
  .child("ingredients")
  .orderByChild("ingredient_name")
  .equalTo(ingredientToBeUpdate)
  .addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot ingredientSnapshot: dataSnapshot.getChildren()) {
            ingredientSnapshot.getRef().child("availability").setValue(1);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException();
    }
}

Also see:

• Firebase Android, set value where x = x?
• Is it possible to update a specific child's value without ID or key in firebase realtime database from android on button click?