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Retrive firebase realtime data to android studio java app interface

I need to get the specific user data using the user email on the real time database. This is my code, This code running without errors but the data is not display in the interface.I think datasnapshot retrieving part is not correct. please help me to solve this.
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
String userEmail = user.getEmail();
DatabaseReference rootReference = FirebaseDatabase.getInstance().getReference();
Query myUsersQuery = rootReference.child("Children").orderByChild("childrenParentEmail").equalTo(userEmail);
myUsersQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String name = dataSnapshot.child("Children").getValue(String.class);
childrenNameEdt.setText(name);
childrenBirthdayEdt.setText(dataSnapshot.child("childrenBirthday").getValue(String.class));
childrenParentNameEdt.setText(dataSnapshot.child("childrenParentName").getValue(String.class));
childrenParentAddressEdt.setText(dataSnapshot.child("childrenParentAddress").getValue(String.class));
childrenParentContactNumberEdt.setText(dataSnapshot.child("childrenParentContactNumber").getValue(String.class));
childrenParentEmailEdt.setText(dataSnapshot.child("childrenParentEmail").getValue(String.class));
childrenTransportTypeEdt.setText(dataSnapshot.child("childrenTransportType").getValue(String.class));
childrenTransportContactNumberEdt.setText(dataSnapshot.child("childrenTransportContactNumber").getValue(String.class));
//childrenID.setText(dataSnapshot.child("password").getValue(String.class));
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
throw error.toException();
}
});

When you execute a query against the Firebase Realtime Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result.
Your code will need to handle that list, by looping over dataSnapshot.getChildren(). So something like:
myUsersQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot: dataSnapshot.getChildren();
String name = snapshot.child("Children").getValue(String.class);
childrenNameEdt.setText(name);
...

How do I get boolean value if given string is child of given firebase location without downloading whole datasnapshot in firebase?

I need to get only true or false value, if a given String is a child of Firebase node, without getting the whole DataSnapshot of the whole node. This is for reducing the cost of Firebase Realtime download.
Firebase database structure
What I had tried:
VillazRef.child(**UID2**).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot)
{
if (dataSnapshot.child(VISIBLE).hasChild("OMBsclV...0X6w2"))
{
bool=true;
}
if (dataSnapshot.child(INVISIBLE).hasChild("OMBsclV...0X6w2"))
{
bool=true;
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
I think these cades VillazRef.child(**UID2**).addListenerForSingleValueEvent return the whole datasnapshot of this location, but I don't want this, its totally a waste of my bandwidth, so
I need only like
if("OMBsclV...0X6w2" is within the VillazRef.child(**UID2**))
{
bool=true;
}
else
{
bool=false;
}

You're almost there. All you need to do is to go a step deeper into your database hierarchy. Assuming that the following line of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
Will return "cxhcK ... kj433" being the UID of the logged-in user (UID2), to check if "OMBsc ... 0X6w2" is a child of the "visible" node, then please use the following lines of code:
String uidToSearch = "OMBsc ... 0X6w2";
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidToSearchRef = rootRef.child("Villaz")
.child(uid)
.child("visible")
.child(uidToSearch);
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exists()) {
bool = true;
} else {
bool = false;
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
}
};
uidToSearchRef.addListenerForSingleValueEvent(valueEventListener);
In this way, you only download a single value from the database and not the entire "visible" node. However, since Firebase API is asynchronous, the value of "bool" cannot be simply used outside the "onDataChange()" method. To be able to use that value outside the callback, please check my answer from the following post:
How to return DataSnapshot value as a result of a method?

How to link each user to their data in Firebase?

I'm trying to set up an order placing system.
Once the user is verified via email, it can create/update/delete order.
Order is saved into Firebase Real-time Database and users are saved in Authentication.
I would like to allow user to only see/edit orders that were placed by this specific user. Basically make use of UserUID from Authentication section.
public class FirebaseDatabaseHelper {
private FirebaseDatabase mDatabase;
private DatabaseReference mReferenceOrders;
private List<Order> orders = new ArrayList<>();
public interface DataStatus{
void DataIsLoaded(List<Order> orders, List<String> keys);
void DataIsInserted();
void DataIsUpdated();
void DataIsDeleted();
}
//Initialize Database object
public FirebaseDatabaseHelper() {
mDatabase = FirebaseDatabase.getInstance();
mReferenceOrders = ((FirebaseDatabase) mDatabase).getReference("order");
}
public void readOrders(final DataStatus dataStatus){
mReferenceOrders.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
orders.clear();
List<String> keys = new ArrayList<>();
for(DataSnapshot keyNode : dataSnapshot.getChildren()) {
keys.add(keyNode.getKey());
Order order = keyNode.getValue(Order.class);
orders.add(order);
}
dataStatus.DataIsLoaded(orders,keys);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
public void addOrder(Order order, final DataStatus dataStatus) {
String key = mReferenceOrders.push().getKey();
mReferenceOrders.child(key).setValue(order).addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
dataStatus.DataIsInserted();
}
});
}
// Update and Delete methods
public void updateOrder(String key, Order order, final DataStatus dataStatus){
mReferenceOrders.child(key).setValue(order).addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
dataStatus.DataIsUpdated();
}
});
}
public void deleteOrder(String key, final DataStatus dataStatus){
mReferenceOrders.child(key).setValue(null).addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
dataStatus.DataIsDeleted();
}
});
}
}
Here's what I was thinking:
When a user creates a new order then a UserUID is added to a database and nested inside 'order' so now each order can be assigned to a user that created it.
Now the next step would be to display this order to a user that created it but only if cust_id (in order) matches UserUID of a logged in user. Would that be a good approach?

Yes, it is a good approach, now you need to add to your Firebase Realtime Database now branch with your users data based on userUID, like this:
Thanks to this you will be able to connect your users with their orders data and besides you can save here more specific user data like "how many orders user create", "how many orders are active" etc.

I have added a user_id to an 'order' in the Firebase database so each order can be assigned to its user.
I got the parameter for user_id by fetching a UserUID from an Authentication section of Firebase when a new user is logged/signed in.
Screenshot of UserUID in Authentication section of Firebase
I got this value in my code by adding the following:
private FirebaseAuth mAuth;
order.setUser_id(mAuth.getCurrentUser().getUid());
Once I got the user_id assigned to each order I've created a following if statement which is implemented in my readOrders function which you can see in my original post above:
public void readOrders(final DataStatus dataStatus){
mReferenceOrders.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
orders.clear();
List<String> keys = new ArrayList<>();
for(DataSnapshot keyNode : dataSnapshot.getChildren()) {
keys.add(keyNode.getKey());
Order order = keyNode.getValue(Order.class);
**if (order.getUser_id().equals(mAuth.getUid())) {
Log.d("FirebaseDatabaseHelper", "match");
orders.add(order);
}else {
Log.d("FirebaseDatabaseHelper", "error");
}**
}
dataStatus.DataIsLoaded(orders,keys);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
So basically now when the new user logs in, there will be nothing to show because the user_id won't match with any of the user_id's inside Order database.
I'm not sure how efficient this method will be when more users/orders will be added so I'll have to do some testing.
Please advise if this is the best approach!

How to fetch data from firebase real time database in android

I have to fetch all children data from firebase real time database? I want to fetch received messages of User2. How to do that? Database example is as given below -

To be able to fetch the children data, try the following:
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("users").child("User1").child("MSG_TYPE_SENT");
reference.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
String msgContent=datas.child("msgContent").getValue().toString();
String msgType=datas.child("msgType").getValue().toString();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
This will give you the msgContent and the msgType, to retrieve any data from the database, you need to pass through every node example:-
getReference("users").child("User1").child("MSG_TYPE_SENT");
Then you can loop inside the ids and retrieve the data.

Here you can fetch the User2 Messages Received
DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference("users");
mDatabase.child("User2").child("MSG_TYPE_RECEIVED").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot spanshot : dataSnapshot.getChildren()){
String content=snapshot.child("msgContent").getValue(String.class);
String type=snapshot.child("msgType").getValue(String.class);
//then you can log those values
Log.d("Values:",""+content+""+type);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
If the message received change at any time (lets say you want to implement the delete option in realtime of the message like whatsapp) .addValueEventListener will update your UI in realtime if you have coded to show that the message has been deleted

Retrieve Java object by ID from Firebase

I am writing an Android app and I am trying to retrieve an object of the class User.java by ID from its Firebase pertinent table. I would like to know how to get it from Java side, as long as I tried the examples stated in Firebase Official docs but none of them is working for me.
Taking this SO question as example, I want a method with the following interface:
public User readUser(String userId);
In other words, I want to execute:
readUser(-lnnROTBVv6FznK81k3n)
and retrieve the associated User object
Thanks
--------------------------------------------------------------EDIT--------------------------------------------------------------:
I managed to get the value with this code:
public void retrieveUser(final String email){
firebaseUsersRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot messageSnapshot: dataSnapshot.getChildren()) {
if(messageSnapshot.getKey().equals(Email.encodeID(email))){
retrievedUser = messageSnapshot.getValue(User.class);
break;
}
}
}
#Override
public void onCancelled(FirebaseError firebaseError) { }
});
}
Please not retrievedUser is a class attribute, thus a field. I am accessing that field from the code, but even I see it takes the value on the debugger, it is being null on the calling code.
Any hint? Can´t I just return it in the method itself, so it would be?:
public User retrieveUser(final String email);
Thanks

so here is the soultion, I didn't put it in a method though.
final String uid = "your Uid here";
// Get a reference to users
Firebase ref = new Firebase(Constants.FIREBASE_URL_USERS);
// Attach an listener to read our users
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
for (DataSnapshot user: snapshot.getChildren()) {
//this is all you need to get a specific user by Uid
if (user.getKey().equals(uid)){
wantedUser = user.getValue(User.class);
}
//**********************************************
}
Log.i(TAG, "onDataChange: " + wantedUser.getName());
}
#Override
public void onCancelled(FirebaseError firebaseError) {
System.out.println("The read failed: " + firebaseError.getMessage());
}
});