我想按值从 Firebase 实时数据库中删除值我没有它的关键

Question

I want to delete value from firebase realtime database by value I don't have it's key

I have database like:

-root
  |
   --fittingHeight
     |
      --"timeStamp1":"1.1"
     |
      --"timeStamp2":"2.1" 

I want to delete 1.1 in this database but without key (timestamp1)

Answer 1

You need to query the collection and then order it by its key

 Query dbQuery = myRef.orderByKey();

Then you will need to add it a listener and use for loop on the results

dbQuery.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for(DataSnapshot dst : dataSnapshot.getChildren()){
            if(...)
                myRef.child(dst.getKey()).removeValue();
                    }
            }
       }

This will remove all the values in that key so if you want to remove a specific value inside that key, add another for loop on its results.

Answer 2

I want to delete 1.1 in this database but without key (timestamp1)

There is no way you can use a query based on a property field which is dynamic. This is happening because, in order to delete a value, you need to know it's key.

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("fittingHeight").orderByChild("timeStamp1").equalTo("1.1");

In Firebase Realtime Database there is no concept of wildcards. So you always need to specify the name of the property. It's true that you can get the content of the entire fittingHeight object and do the filtering on the client but this solution isn't practical at all. A solution might be to change the database schema to have fixed properties, in a way that the above query can work.