what is the idiom to query a Firebase DatabaseReference?

Question

not an android question.

Method intended to query the database:

private void db() throws FileNotFoundException, IOException {
    FileInputStream serviceAccount = new FileInputStream("serviceAccountKey.json");
    FirebaseOptions options = new FirebaseOptions.Builder()
            .setCredential(FirebaseCredentials.fromCertificate(serviceAccount))
            .setDatabaseUrl(stringURL)
            .build();

    log.info(options.toString());

    FirebaseApp firebaseApp = FirebaseApp.initializeApp(options);
    FirebaseDatabase f = FirebaseDatabase.getInstance(firebaseApp, stringURL);

    DatabaseReference databaseNonRoot = f.getReference();
    DatabaseReference databaseReference = databaseNonRoot.getRoot();

    log.info(databaseReference.toString());

    //    databaseReference.addValueEventListener(new ValueEventListener(){
    //really?
}

I've entered data manually through the web interface. How do I query Firebase? Something analogous to SELECT * FROM <TABLE> is what I'm looking for.

JSON data export:

{
  "abc" : 123,
  "bar" : 4342342,
  "foo" : 432434
}

see also:

how to get all child list from Firebase android

In general interacting with the Firebase Database is the same between Android and other Java environments. Reading lists of data is explained here: https://firebase.google.com/docs/database/android/lists-of-data#child-events and here: https://firebase.google.com/docs/database/admin/retrieve-data#section-event-types What does your data structure look like (as JSON text, no screenshots please)? You can get this by clicking the "Export JSON" link in your [Firebase Database console](https://console.firebase.google.com/project/_/database/data). — Frank van Puffelen, Jul 02 '17 at 22:35
I'll update momentarily with JSON. If I can get the JSON tree that will get me headed in the right direction. — Thufir, Jul 02 '17 at 22:41

score 2 · Accepted Answer · answered Jul 03 '17 at 02:15

2

Yes. Really.

databaseReference.addValueEventListener(new ValueEventListener(){
  @Override
  public void onDataChange(DataSnapshot dataSnapshot) {
    for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
      System.out.println("Key="+childSnapshot.getKey()+" Value="+childSnapshot.getValue());
    }
  }

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

See the Firebase documentation on dealing with lists for more information. I also recommend reading my answer here: https://stackoverflow.com/a/30943084/209103

answered Jul 03 '17 at 02:15

Frank van Puffelen

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does this only listen for changes or does it query the actual JSON tree in its entirety? – Thufir Jul 04 '17 at 00:54
The `onDataChange` fires for the initial data and for any subsequent change. – Frank van Puffelen Jul 04 '17 at 02:43

what is the idiom to query a Firebase DatabaseReference?

1 Answers1