Develop Reference

Retrieve the IDs of a user's friends and show in RecyclerView the data of each friend (Firebase)

In the Firebase, I have a “usuario” node with the data for each registered user. I want to retrieve the Ids of a user's friends and through these ID's show in RecyclerView the data of each friend (identifier, name and photo address).
My structure in Firebase:
I tried this code, but it doesn't work. the list is empty:
ref = ConfigFirebase.getFirebaseDatabase().child("usuarios"); //code in OnCreate
//My method
ref = ref.child(idUserLog).child("friends");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot idFriends: dataSnapshot.getChildren()){
DataUserFriend dataUserFriend = idFriends.getValue(DataUserFriend.class);
String id = dataUserFriend.getIdUser();
ref.child(id).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
DataUser dataUser = dataSnapshot.getValue(DataUser.class);
listFriends.add(dataUser);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}
listFriendsAdapter.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
What is wrong? or should i try another way?
Solution:
ref = ConfigFirebase.getFirebaseDatabase().child("usuarios"); //code in OnCreate
//My method
ref = ref.child(idUserLog).child("friends");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
final int numFriends = (int) dataSnapshot.getChildrenCount();
if(numFriends != 0){
for (DataSnapshot idFriends: dataSnapshot.getChildren()){
DataUserFriend dataUserFriend = idFriends.getValue(DataUserFriend.class);
String id = dataUserFriend.getIdUser();
ref = ConfigFirebase.getFirebaseDatabase().child("usuarios").child(id);
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
DataUser dataUser = dataSnapshot.getValue(DataUser.class);
listFriends.add(dataUser);
if(listFriends.size() == numFriends){
listFriendsAdapter.notifyDataSetChanged();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});

The call to listFriendsAdapter.notifyDataSetChanged() should happen in the same method that updates listFriends.
So:
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot idFriends: dataSnapshot.getChildren()){
DataUserFriend dataUserFriend = idFriends.getValue(DataUserFriend.class);
String id = dataUserFriend.getIdUser();
ref.child(id).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
DataUser dataUser = dataSnapshot.getValue(DataUser.class);
listFriends.add(dataUser);
listFriendsAdapter.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
}
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
If you want to call listFriendsAdapter.notifyDataSetChanged() only when all friends have been added to listFriends, you can keep a count of how often the inner onDataChange has been called and compare that to the number of friend IDs.

You have added SingleValueEvent listener on database reference object due to which the callback isn't getting fired immediately. You should create a Query and add the SingleValueEvent listener for it. For example:
DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference("usuarios");
Query query = mDatabase.child(idUserLog).child("friends");
query .addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
// Code to parse and display data
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});

Jump to Firebase parent Nodes from Child Nodes

Hello all i have a my fire-base structure like this
Firebase Database
I have an array list inside an node in fire-base , I need to loop through this list and jump to each ID to get information i need like the database photo shows.
what I've tried so far
public static void checkIfCurrentUserLiked(final HomeFragment.PostsViewHolder postsViewHolder, String postKey) {
userID = Objects.requireNonNull(FirebaseAuth.getInstance().getCurrentUser()).getUid();
likesRef = FirebaseDatabase.getInstance().getReference().child("likes");
postsRef = FirebaseDatabase.getInstance().getReference().child(postKey);
postsRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild("likes")) {
for (DataSnapshot ds : dataSnapshot.child("likes").getChildren()) {
likesRef.child(Objects.requireNonNull(ds.getValue()).toString())
.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
Like like = snapshot.getValue(Like.class);
if (like != null && like.getLikedUserID().equals(userID)) {
postsViewHolder.likesImage.setImageResource
(R.drawable.ic_item_home_post_like_filled);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) { }
});
}
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) { }
});
}
i have no error , just nothing happens , data are not fetched as expected

Change this:
postsRef = FirebaseDatabase.getInstance().getReference().child(postKey);
into this:
postsRef = FirebaseDatabase.getInstance().getReference().child("posts").child(postKey);
According to your database, you have node posts before the postKey, therefore you need to add it when referencing to a location.

how to read all child nodes values and use them in firebase android

This is my Database in Firebase
I want to get the values of Students under Courses
and then I want to delete the course name under courses in users(that username match the values I got from Courses/Students )
after clicking on a button
This is my code
DatabaseReference mCourseDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Courses").child(courseModel.getCourseName());
final DatabaseReference mStudentDB = FirebaseDatabase.getInstance().getReference().child("Users");
mCourseDatabaseReference.child("Students").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for(final DataSnapshot snapshot1 : dataSnapshot.getChildren()){
final User student = snapshot1.getValue(User.class);
mStudentDB.orderByChild("userName").equalTo(student.getUserName()).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot data: dataSnapshot.getChildren())
{
String stuserkey = data.getKey();
mStudentDB.child(stuserkey).child("Courses").child(courseModel.getCourseName()).removeValue();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) { }});
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) { }});
but it doesn't work.
can you help me, please?
thanks.

firebase, database, android studio: Not reading data from firebase database

I have data in database:
database in firebase
I want read all child (Belgia, Czechy, Polska...) and display it in Text Field, but AFTER click the button (I don't change data in database).
The button have assigned below function:
public void f_btn_zaczytaj_dane(View view) {
myRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String value = dataSnapshot.getValue(String.class);
TextView txt_opis_panstwa = (TextView) findViewById(R.id.txt_opis_panstwa);
txt_opis_panstwa.setText(value);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
Befrore i write in code:
FirebaseDatabase database;
DatabaseReference myRef;
database = FirebaseDatabase.getInstance();
myRef = database.getReference("kraj");
Unfortunately, when I press the button nothing happens.
I will be grateful for the help
Regards, Marcin

You have to iterate through your children
public void f_btn_zaczytaj_dane(View view) {
myRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
TextView txt_opis_panstwa = (TextView) findViewById(R.id.txt_opis_panstwa);
for (DataSnapshot country : dataSnapshot.getChildren()) {
txt_opis_panstwa.append(country.getKey());
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}

Please use this code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference krajRef = rootRef.child("flagiistolice").child("kraj");
public void f_btn_zaczytaj_dane(View view) {
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
TextView txt_opis_panstwa = (TextView) findViewById(R.id.txt_opis_panstwa);
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String country = ds.getkey();
txt_opis_panstwa.append(country);
Log.d("TAG", country);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
krajRef.addListenerForSingleValueEvent(eventListener);
}

How to use multiple orederbychild in Firebase database?

Hello Everyone I am using firebase database in my app. I am able to add data to database. Now I want to implement search in my app, I have two option for search users,
1)Blood Group
2)User Area
I am able to get data as per blood group selection, but I don't know how can I fetch data with blood group and area. (Multiple Selection Filter)
Now if the user will select 'A+' as blood group from spinner and select Area 'ABC'
Then result would come as Users with 'A+' blood group and 'ABC' area.
search_button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
System.out.println("Default Selected"+sel_blood_group);
mFirebaseDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Your Logic here
for (DataSnapshot eventSnapshot : dataSnapshot.getChildren()) {
UserRegisterModel mModel = eventSnapshot.getValue(UserRegisterModel.class);
// Log.e("DATA" ,""+ mModel.getName());
}
Query chatRoomsQuery = mFirebaseDatabase.orderByChild("blood_group").equalTo(sel_blood_group);
chatRoomsQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
// dataSnapshot is the "issue" node with all children with id 0
for (DataSnapshot issue : dataSnapshot.getChildren()) {
// do something with the individual "issues"
UserRegisterModel mModel = issue.getValue(UserRegisterModel.class);
Log.e("QUERY DATA" ,""+ mModel.getName());
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Log.e("DATA" ,""+ chatRoomsQuery.toString());
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});

Firebase RealTime Database does not support multiple where clauses. So try to query with one filter and then filter the next one programatically.
search_button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
System.out.println("Default Selected"+sel_blood_group);
System.out.println("Default Selected"+sel_area);
mFirebaseDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Your Logic here
for (DataSnapshot eventSnapshot : dataSnapshot.getChildren()) {
UserRegisterModel mModel = eventSnapshot.getValue(UserRegisterModel.class);
// Log.e("DATA" ,""+ mModel.getName());
}
Query chatRoomsQuery = mFirebaseDatabase.orderByChild("blood_group").equalTo(sel_blood_group);
chatRoomsQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
// dataSnapshot is the "issue" node with all children with id 0
for (DataSnapshot issue : dataSnapshot.getChildren()) {
// do something with the individual "issues"
UserRegisterModel mModel = issue.getValue(UserRegisterModel.class);
if(mModel.getArea().equals(sel_area))
Log.e("QUERY DATA" ,""+ mModel.getName());
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Log.e("DATA" ,""+ chatRoomsQuery.toString());
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});enter code here

You can make userName to be added only once using the following method. I have assumed that you are storing the user details in UserRegisterModel class. Please take care of the DatabaseReferences as I have used what you have mentioned and I am not aware of your Database structure.
Query chatRoomsQuery = mFirebaseDatabase.orderByChild("User_Name").equalTo(userRegisterModel.getUserName());
chatRoomsQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Log.e("UserAlready Registered");
}
else
{
mFirebaseDatabase.push().setValue(userRegisterModel);;
Log.i("User added Successfully");
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
I have not tested the code but I think it will work! :)