Develop Reference

how to check the current Firebase data under uid?

I am trying to check uid from firebase Realtime database, but its only returns the current uid and when I try to check uid with previous uid then also it only returns the current uid. I had tried many ways and searched but I can't get the exact solution, please if any one could help.
here what I am using to check the uid
FirebaseAuth.getInstance().getCurrentUser().getUid();
here is my code how I am trying to check
String userEnteredUserName = binding.textLoginUserName.getEditText().getText().toString().trim();
String userEnteredPassword = binding.textPassword.getEditText().getText().toString().trim();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");
Query checkUser = reference.child(FirebaseAuth.getInstance().getCurrentUser().getUid()).orderByChild("userName").equalTo(userEnteredUserName);
Log.d("uids", "uid: " + uid);
checkUser.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
binding.textLoginUserName.setError(null);
binding.textLoginUserName.setErrorEnabled(false);
Log.d("users", "Username: " + snapshot.toString());
if (snapshot.exists()) {
String passwordFromDB = snapshot.child(userEnteredUserName).child("password").getValue(String.class);
if (passwordFromDB.equals(userEnteredPassword)) {
//next activity
}else{
Toast.makeText(Login.this, "Error", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
Toast.makeText(Login.this, "Error", Toast.LENGTH_SHORT).show();
}
});
In log what I get,
2022-02-06 13:13:06.173 18093-18093/abc C/uids: uid: OFtpR6bfISP3Odd9K1oGWCQmeEf2
Here is my firebase data, "aisha12" is working which is under the current uid but when I try to check "vgbb" it returns only the current uid

If I understand correctly, you are trying to allow a user to register a username and ensuring that the username is unique. Your current data structure doesn't allow you to do that query though.
Firebase Realtime Database can only order/filter on a value that is at a fixed path under each child node of the location you query. So in your current code:
reference.child(FirebaseAuth.getInstance().getCurrentUser().getUid()).orderByChild("userName").equalTo(userEnteredUserName);
You are querying the direct child nodes of /Users/$uid looking for the username under there. Since you're specifying the UID in that path, you're only searching under that specific user.
There is no way with your current data structure to search across all /Users, since the property you are looking for is under /Users/$uid/$username/userName, so with two dynamic keys in there, and the database can only handle one dynamic key.
To allow the query, you will need to change the data structure and remove the $userName level from it, so that you get:
Users: {
"3l6Rm....": {
"userName": "vgbb",
...
},
"OftpR...": {
"userName": "aisha12",
...
}
}
Now you can search for the username with:
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");
Query checkUser = reference.orderByChild("userName").equalTo(userEnteredUserName);
I also recommend checking out these previous questions on allowing a user to register a unique username:
How do you prevent duplicate user properties in Firebase?
Firebase security rules to check unique value of a child #AskFirebase
How to check if usernames are unique in Firebase
unique property in Firebase
How to give unique usernames from a list of usernames to the users in the firebase
Check value already exists or not in Firebase?

How do you manage your android device token generated by FCM after token expired?

I'm developing a push notification app, do you have same issue:
My app generate a FCM device token and store it in a cloud database, so I can send notification messages to a device via FCM, and my database table looks like:
userid | device_token
Mary | xxxxxxxxxxxxxxxxxxxxxxxxxxxx // token1, from Mary's first device
John | yyyyyyyyyyyyyyyyyyyyyyyyyyyy
Mary | zzzzzzzzzzzzzzzzzzzzzzzzzzzz // token2, from Mary's second device
Mary | kkkkkkkkkkkkkkkkkkkkkkkkkkkk // token, from Mary's first device
.......
After Mary reinstalled this app from her first device, a new device token generated, and it is stored with token3.
How can I remove the expired device token token1, the only information I got may only be a pair of device token and an account name.
So how do you manage your device in this situation?

If "Mary" is using the same account to log in each time in your app, even if it is a new phone or reinstalled app why do you create a new token field inside the database? Why don't you always write inside the same token field so you always have access to this field. This will also send notifications only to the phone that your user is actually using right now. So each time when the user starts the app check token, if not equal write the new one inside your database. And from the server-side take those tokens and send notifications.
Am I missing something?
To do this, I would suggest using FirebaseAuth for the SignIn and SignUp process of your application. Then use generated uid as the field ID for the user inside the Realtime Database. You can get this uid with FirebaseAuth.getInstance().getCurrentUser().getUid(). So your user Mary will always have the same uid no matter what phone she uses. Always find the user inside the database with this uid and overwrite the existing Firebase token. This also means that your "users" will not be a single line field inside the database, but a more complex and better representation of a user. You can use model classes for this like:
public class User {
public long id = 0;
public long account_id = 0;
public String account_name = "";
public String first_name = "";
public String last_name = "";
public String email_address = "";
public String password = "";
public User() {
}
}
It's up to you on how to configure this. But using models is also helping you on posting and retrieving data, like this:
Creating new user:
DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
mDatabase.child("users").child(FirebaseAuth.getInstance().getCurrentUser().getUid()).setValue(user);
Retrieving data from the real-time database:
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference databaseUsers = database.child("users");
User myUser = null;
Query usersQuery = databaseUsers.orderByChild("username").equalTo(uid); //you can use any value to order as you want, or you don't have to, there is many options for this query
usersQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChanged(#NonNull DataSnapshot snapshot) {
try {
for (DataSnapshot user : snapshot.getChildren()) {
myUser = user.getValue(User.class);
}
} catch (Exception e) {
e.printStackTrace();
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
}
});

Inspired by this: Firebase Cloud Messaging - Managing Registration Tokens
When a token generated:
if Mary logged in:
add the device to the "Mary" Device Group.
store the device group id and connect the device group id to "Mary"'s profile in database.
if app server need to send notification to Mary, just send to the Device Group, the benifit is that you don't need to check if the device token is valid or not, Firebase Cloud Messaging discards invalid device tokens.
if no one logged in:
do nothing or just store the device token.

How can I orderByChild on Android Firebase chat based application?

I'm trying to build a user to user chat application, but I'm not able to order the chat list by last message sent.
My Firebase (real time) structure is like this:
I'm trying to retrieve the data like this, but i'm not able to order by "timestamp" in the inner message.
final String uID = firebaseAuth.getCurrentUser().getUid();
Query ref = FirebaseDatabase.getInstance().getReference("Messages");
ref.orderByChild("timestamp").startAt(uID).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
Did anyone knows how can I order the list of users by the timestamp of the last message?

You need to change the query to the following:
final String uID = firebaseAuth.getCurrentUser().getUid();
Query ref = FirebaseDatabase.getInstance().getReference("Messages");
ref.child(uID_uID).orderByChild("timestamp").addValueEventListener(new ValueEventListener() {
You need access to the direct node under the node Messages, the node with underscore. Then you can add orderByChild("timestamp").equalTo("157644739279")

How to retrieve and display data from users that are logged in - Firestore

I am trying to get and display my user's information when they are logged in. (i.e: name, email, phone)
I have tried multiple snippets i have found on youtube and on stack overflow but they have failed. Most tutorials use realtime Database, which is not what i am looking for.
I have also tried making a "users" object.
private void getData(){
FirebaseFirestore db = FirebaseFirestore.getInstance();
db.collection("users")
//.document(FirebaseAuth.getInstance().getCurrentUser().getUid())
.whereEqualTo("email:", FirebaseAuth.getInstance().getCurrentUser().getUid())
.get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
for (DocumentSnapshot document : task.getResult()) {
//Toast.makeText(getApplicationContext(),document.getId() +"==>" + document.getData(),Toast.LENGTH_LONG).show();
//Toast.makeText(getApplicationContext(),""+ document.get("Email") ,Toast.LENGTH_LONG).show();
nameEdt.setText((CharSequence) document.get("First Name"));
emailEdt.setText((CharSequence) document.get("Email"));
phoneEdt.setText((CharSequence) document.get("Phone"));
}
} else {
Toast.makeText(getApplicationContext(),"No such document",Toast.LENGTH_LONG).show();
}
}
});
}
Database Structure:
I understand that documents in firestore are not associated with users, but i dont know how to set my code up so that it only retrieves data from the user that is signed in* It works fine for newly created accounts, but if i were to log out and sign in with a different user it will not update the "account/user information".
In short, how would I access and display my database information from signed in users?
Additional Notes: I am using Email and Password for authentication

To access your user data stored in Firestore, it shouldn't be as complicated as you thought, there's no queries needed, you just need to fetch the documents corresponding to the user's uid, and fetch the specific fields or do whatever you need with them, like this:
db.collection("users").document(FirebaseAuth.getInstance().getCurrentUser().getUid())
.get().addOnCompleteListener(task -> {
if(task.isSuccessful() && task.getResult() != null){
String firstName = task.getResult().getString("First Name");
String email = task.getResult().getString("Email");
String phone = task.getResult().getString("Phone");
//other stuff
}else{
//deal with error
}
});
Original Answer:
User information is not stored in the Firestore database, they are associated with the Firebase Authentication which you set up for the log in. To retrieve the related user information, you need to use the related FirebaseAuth APIs. Use this to retrieve the current log in user:
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
Then you can get the name and email with something like this:
String name = user.getDisplayName();
String email = user.getEmail();
For more information, refer to the documentation.
If FirebaseAuth doesn't resolve, that probably means you didn't follow the set up guides correctly and forgot to include the dependency in your gradle file:
implementation 'com.google.firebase:firebase-auth:17.0.0'

After a couple days head butting at trying to find a solution, i have found one that is able to retrieve user information from the database. However it is important to note that because my application is not holding a lot of data so this structure works for me.
So i was essentially on the right track, but with some lack of understanding of firebase i missed a few concepts.
private void getData(){
FirebaseFirestore db = FirebaseFirestore.getInstance();
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
final String current = user.getUid();//getting unique user id
db.collection("users")
.whereEqualTo("uId",current)//looks for the corresponding value with the field
// in the database
.get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
for (DocumentSnapshot document : task.getResult()) {
nameEdt.setText((CharSequence) document.get("firstName"));
emailEdt.setText((CharSequence) document.get("email"));
phoneEdt.setText((CharSequence) document.get("phone"));
// These values must exactly match the fields you have in your db
}
}
As mentioned before, documents do not associate with users, but you CAN link them together by creating a field in your db called "whatever your want" (i made mine uId). This is because firebase generates a unique id for each user when authenticated. By creating a field that holds that unique id you are able to retrieve the associated information in that collection.
How to create the field:
I created a "user" object that would grab the uid from my edit text. In my code, i passed the uid wherever i was creating/authenticating a new user/account.
FirebaseUser testUser = FirebaseAuth.getInstance().getCurrentUser(); //getting the current logged in users id
String userUid = testUser.getUid();
String uidInput = userUid;
User user = new User(firstNameInput,lastNameInput,uidInput);
db.collection("users").document(userUid)
.set(user)
.addOnSuccessListener(new OnSuccessListener<Void>() {
note: I believe you can also add it to your hash map if you have it done that way.

How to prevent duplicate data in Firebase Database for Android

I have a database in Firebase for Android and I have an object with the attributes you see in the image. An object is stored in the database with the following code:
FirebaseUser user = mAuth.getCurrentUser();
String videoId = getIntent().getStringExtra("VIDEO_ID");
minuto = player.getCurrentTimeMillis();
Watching watching = new Watching(user.getUid(), videoId, String.valueOf(minuto));
DatabaseReference mRef = database.getReference().child("Watching").push();
mRef.setValue(watching);
The problem I have is as I am using push() to store the nodes I am having duplicate data as you can see in the image.
Is there any way to avoid storing duplicate data? Knowing that I don't have my own ID to store.
Any help ?

It depends on how you define a duplicate.
A common case where people have this question is when they're storing users. There the definition of a duplicate is simple: if two user objects have the same value for uid, they're the same user. So in that case you should store the users under their uid, instead of under a push ID.
The same applies for your situation. If a single user can only watch a single video, store the nodes under Watching by the uid of the user:
Watching
"NX7...A33"
"idVideo": "b13...o4s"
"minute": "0"
But if it's the combination of uid + idVideo that is unique, store the nodes under a combined key:
Watching
"NX7...A33_b13...o4s": "0"
Now you can easily prevent duplicates, by using setValue() instead of push():
String key = user.getUid() + "_" + videoId;
ref.child("Watching").child(key).setValue(String.valueOf(minuto));

I was facing same problem like you and this is how i figure it out. I m checking email address that user entered with the one saved in my db.if any match found then show toast that email already exists otherwise save with new key.
mFirebaseDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(final DataSnapshot dataSnapshot) {
for (DataSnapshot data : dataSnapshot.getChildren()) {
//If email exists then toast shows else store the data on new key
if (!data.getValue(User.class).getEmail().equals(email)) {
mFirebaseDatabase.child(mFirebaseDatabase.push().getKey()).setValue(new User(name, email));
} else {
Toast.makeText(ChatListActivity.this, "E-mail already exists.", Toast.LENGTH_SHORT).show();
}
}
}
#Override
public void onCancelled(final DatabaseError databaseError) {
}
});