Develop Reference

Android Firebase push and get Array List

I have a questions how could i push array list to my freebase data base
and also read it to add a new element , then push it again.
In the above photo you can see i have added array list joinedStudents
and i need to read it and push new elements to it
I've tried the following
DatabaseReference requestsRef = FirebaseDatabase.getInstance().getReference();
requestsRef.child("requests").child(requestID).child("joinedStudents");
requestsRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot d : dataSnapshot.getChildren()) {
String jR = d.getValue(String.class);
joinedStudents.add(jR);
}
joinedStudents.add(studentID);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d(TAG, "error fetching data from firebase");
}
});
for (String string : joinedStudents) {
requestsRef.child("requests").child(requestID).child("joinedStudents").setValue(string);
}
but it's not working

I believe you have your references slightly mixed up. Try something like:
DatabaseReference joinedStudentsRef = FirebaseDatabase.getInstance().getReference().child("requests").child(requestID).child("joinedStudents");
joinedStudentsRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot d : dataSnapshot.getChildren()) {
String jR = d.getValue(String.class);
joinedStudents.add(jR);
}
joinedStudents.add(studentID);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d(TAG, "error fetching data from firebase");
}
});
for (String string : joinedStudents) {
joinedStudentsRef.child("1").setValue(string); // setValue is for key, value
// but you have an array
}
Where your reference is now the direct node that you want to monitor/read/write

Retrieve first child from a parent in Firebase

I am working on an Android application. I want the first child (first UID) of the parent 'support' and store it in a String variable. How do I get the value of the first UID from the list?
I tried one approach. It doesn't work though.
#Override
public void onDataChange(DataSnapshot dataSnapshot1) {
if (dataSnapshot1.exists()) {
String futureUID = "";
for(DataSnapshot futureUIDdatasnapshot:dataSnapshot1.getChildren() ){
futureUID = futureUIDdatasnapshot.getKey();
break;
}
/*Getting the first UID from the list of UID's in queue in 'future'*/
futureUID = dataSnapshot1.getChildren().iterator().next().getKey();
/*Moving a card from 'future' to 'serving'*/
societyServiceUIDReference.child(FIREBASE_CHILD_SERVING).child(futureUID).setValue(FIREBASE_ACCEPTED);
/*Removing the UID from 'future' after it is placed in 'serving'*/
societyServiceUIDReference.child(FIREBASE_CHILD_FUTURE).child(futureUID).removeValue();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
NOTE: 'futureUID' is the UID I want

Try the following:
DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("support");
Query queryUid=ref.orderByKey().limitToFirst(1);
queryUid.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot datas : dataSnapshot.getChildren()) {
String key=datas.getKey();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

Try
DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();
.orderByKey().limitToFirst(n) is what does the trick. It orders the query results by key and returns only the first n results; in this case 1
mDatabase.getChild("support").orderByKey().limitToFirst(1)
.addListenerForSingleValueEvent(new ValueEventListener () {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exists()){
for (DataSnapshot supportItem: dataSnapshot.getChildren()) {
String futureUID =supportItem.getKey();
}
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
//Catch your error here
}
});
see Work with Lists of Data on Android

How to handle a json returning data objects with firebase in android

I have an android application which does the following:
com.google.firebase.database.Query query = mUsersRef
.orderByChild(USER_TABLE_EMAIL)
.startAt(searchTerm)
.endAt(searchTerm + FirebaseConstants.SEARCH_ESCAPE);
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
DataSnapshot d = dataSnapshot;
getView().showSearchResults();
}
#Override
public void onCancelled(DatabaseError databaseError) {
// TODO: something?
}
});
I was wondering what the simplest way to convert dataSnapshot into User objects was. Do I need to get returned json and do some form of conversion? or is there a better way?

You can convert your data snapshot into an object as shown below:
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot snapShot : dataSnapshot.getChildren()){
User user = snapShot.getValue(User.class);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// TODO: something?
}
});

Firebase query in query

I am trying to make multiple queries to my Firebase database, but it seems I am doing something wrong, and I just can't seem to understand what.
My code is this:
database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("Tbl1");
Query tbl1Query = ref.orderByChild("type");
tbl1Query .addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for (DataSnapshot singleSnapshot : dataSnapshot.getChildren()) {
Tbl1Item item = singleSnapshot.getValue(Tbl1Item .class);
tbl1List.add(item);
}
DatabaseReference ref = database.child("Tbl2");
Query tbl2Query = ref.orderByChild("status");
tbl2Query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for (DataSnapshot singleSnapshot : dataSnapshot.getChildren()) {
tbl2Item item = singleSnapshot.getValue(tbl2Item.class);
tbl2List.add(item);
}
DatabaseReference ref = database.child("Tbl3");
Query tbl3Query = ref.orderByChild("status");
tbl3Query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for (DataSnapshot singleSnapshot : dataSnapshot.getChildren()) {
tbl3item item = singleSnapshot.getValue(tbl3item.class);
tbl3List.add(item);
}
SortTableData();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
The problem is that the app crashes though I get no error in console.
What I am trying to obtain, is create 3 lists of objects with data from table1, table2 and table3 and then call a method that will process that data.
If I remove the 2nd and 3rd queries, everything works fine, but I don't have all the needed data... so what I am doing wrong?

Displaying the database nodes from Firebase in a list in Android

A simple question:
Referring to my database image, I want to get the values of the children of node "user" in a list in an Activity, i.e. values "a" and "m" should be displayed in the list.
What should I use and how?

Please try this code:
DatabaseReference yourRef = FirebaseDatabase.getInstance().getReference().child("user");
yourRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<String> usersList = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
String userName = (String) ds.getKey();
usersList.add(userName);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
This is the way in which you'll have in your list, a, m ans so on.
Hope it helps.

You can get the info from the docs here
List<User> allUsers = new ArrayList<>();
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("user");
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
allUsers.clear();
for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) {
allUsers.add(userSnapshot.getValue(User.class));
}
yourRecyclerViewAdapter.notifyDataSetChanged();
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Getting Users failed, log a message
Log.w(TAG, "loadUser:onCancelled", databaseError.toException());
// ...
}
});