Develop Reference

How to create a list of all the saved posts of a particular user using Firebase Realtime Database?

I have a root node named 'Posts'. Then each node inside Posts has a unique postID generated by push(). Now each post has several children. One such child is "saves" in which I have stored the userIDs of those users who have saved this particular post. What I want to do is that I want to create and display a list of all those posts which a particular user has saved.
This means that I have to write a code that will scroll through all posts in 'Posts' node, check for 'saves' child in each post,
if it exists, then check for userID of a particular user in 'saves',
if it exists, then that post should be added to a list called 'mySavedPosts'.
Please click here to see the structure of my 'Posts' node.
I have tried many different ways to achieve this but I am just getting an empty list or app crashes. I cannot post all the different ways that I have tried since that would make this question very lengthy and clumsy, but all my ways revolve somewhere around this approach:
FirebaseDatabase.getInstance().getReference()
.child("Posts")
.child("saves")
.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
mySavedPosts.clear();
if (snapshot.child(FirebaseAuth.getInstance().getCurrentUser().getUid()).exists()){
for (DataSnapshot dataSnapshot : snapshot.getChildren()){
Post post = dataSnapshot.getValue(Post.class);
mySavedPosts.add(post);
}
}
Collections.reverse(mySavedPosts);
postAdapterSaves.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
}
});
I have also tried entering .child(post.getPostID()) after .child("Posts") but that generates a null Pointer Exception.
I have also tried entering .child(auth.getUid()) after .child("saves"), that didn't work too!
I have tried 10s of other modifications but none of them have worked.

According to your comment:
I just need to see if the auth.getUid() is there in the children of "saves".
To check if the UID of the authenticated user exists in the "saves" node, please use the following lines of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference postsRef = rootRef.child("Posts");
Query query = postsRef.orderByChild("saves/" + uid).equalTo(true);
query.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
#Override
public void onComplete(#NonNull Task<DataSnapshot> task) {
if (task.isSuccessful()) {
for (DataSnapshot postSnapshot : task.getResult().getChildren()) {
Post post = postSnapshot.getValue(Post.class);
mySavedPosts.add(post);
}
Collections.reverse(mySavedPosts);
postAdapterSaves.notifyDataSetChanged();
} else {
Log.d("TAG", task.getException().getMessage()); //Don't ignore potential errors!
}
}
});

Delete FireBase Value Without Knowing The Key Name

So I am working on the memories Firebase app and there is a stage where the user can upload photos to his memory. Each photo has uniq name "ImgLink0","ImgLink1",etc..
The function I am working on is to delete a specific photo when I am pressing a long click, but I can't reach the image in Firebase.
I tried like below but I got stuck because I can't identify the image key:
mDatabase.child(userUID).child("Memories").child(memoryName).child("Images").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot imageSnapshot : dataSnapshot.getChildren()) {
String imagesKey = imageSnapshot.getKey();
String imagesValue = (String) imageSnapshot.getValue();
Log.e("Test","" + imagesKey + "" + imagesValue);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
And this is the data structure:
I tried using query too but with no success because I don't have the image key.
Thank you for any help :)

To delete a node from the database, you need to know the completely path to that node.
Assuming you do know the URL of the image to delete, but not the key (ImgLink1 or ImgLink2) that is stored under, you're going to have to use a query to look up that key.
Something like:
DatabaseReference ref = mDatabase.child(userUID).child("Memories").child(memoryName).child("Images");
Query query = ref.orderByValue().equalTo("URL of the image")
query..addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot imageSnapshot : dataSnapshot.getChildren()) {
imageSnapshot.getRef().removeValue();
}
}
...
Also see these related answer:
deleting specific post in database(by post node) but it deletes entire database_table
How can i remove all fields and values by using key value or a field key from firebase realtime database?

To remove the second URL for example, please use the following lines of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference imageToDeleteRef = rootRef
.child(uid)
.child("Memories")
.child("TestMem")
.child("Images")
.child("ImgLink1");
imageToDeleteRef.removeValue().addOnCompleteListener(/* ... */);
So I have created a reference that points exactly to ImgLink1 node and then I called .removeValue() on reference in order to delete it. So there is no need to read the value in order to perform a delete operation.
If you want to read the URL, please use these lines:
imageToDeleteRef.addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
#Override
public void onComplete(#NonNull Task<DataSnapshot> task) {
if (task.isSuccessful()) {
String url1 = task.getResult().child("ImgLink1").getValue(String.class);
Log.d("TAG", url1);
} else {
Log.d("TAG", task.getException().getMessage()); //Don't ignore potential errors!
}
}
});
The result in the logcat will be:
https://firebasestorage.googleapis.com...

How to show each users' data based on their Google account - Firebase

I'm currently building a to-do app on Android Studio. I'm facing an issue with my Firebase database. What I'm trying to do is, each user to have a unique id based on their google sign in, in order to see only their own data. Currently, on my app, everyone can see anyone's' tasks. On Firebase I'm using the Realtime Database, specifying it by one child of "Users" and another one of Task + a random number. Also, I've already added the google sign in button on the launch of my app.
Current Database:
enter image description here
Example of how my hierarchy wants to be:
enter image description here

According to your comments, to get only the Task objects the correspond to a particular user, please use the following lines of code:
String userId = "User-13294";
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference tasksRef = rootRef.child("Users").child(userId).child("Tasks");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot taskSnapshot : dataSnapshot.getChildren()) {
String title = taskSnapshot.child("title").getValue(String.class);
Log.d("TAG", title);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
}
};
tasksRef.addListenerForSingleValueEvent(valueEventListener);
Because User-13294 has only one Task, the result in the logcat will be only one title:
Swimming

Regroupe all data on firebase for each "getKey()" when using them on app

i have a probleme and i don't know how to solve this.
userRef.addValueEventListener(new ValueEventListener(){
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for(DataSnapshot priereSnapshot : dataSnapshot.getChildren()){
//takeFromDataBase
LocationUser locationUser = priereSnapshot.getValue(LocationUser.class);
double longitudeD = Double.valueOf(locationUser.locationUserLongitude);
double latitudeD = Double.valueOf(locationUser.locationUserLatitude);
//createMarkerFromDataBase
LatLng Test = new LatLng(latitudeD, longitudeD);
String idNum = userRef.getKey();
MarkerOptions optionsTest = new MarkerOptions().position(Test).title("Janaza le: " + locationUser.locationUserDate);
map.addMarker(optionsTest).setIcon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_YELLOW));
//createLayoutFromInfoUser
String adresseD = locationUser.locationUserAdresse;
String dateD = locationUser.locationUserDate;
String heureD = locationUser.locationUserTime;
adresse_txt.setText(adresseD);
date_txt.setText(dateD);
heure_txt.setText(heureD);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
It's ok when the marker is getting the date and the hour, but when i want to show other information from the same getkey(), it's not working.
For exemple, when i'm clicking on the marker 3 for (12/07/2020), the app need to put the right information relate to this date on firebase from the same getKey, but it's not working.
the thing is that i don't know how to link all data from the same getkey()
Can you help me please?

I'm not sure I understand correctly, but I think your problem may be here:
String idNum = userRef.getKey();
This gets the key of the userRef, which is the location that you listen to.
More likely you want to get the key of the specific user snapshot, for the current iteration of the loop. To do that, you'll want to get the key of the snapshot:
String idNum = priereSnapshot.getKey();

How to get value of Child of childs from firebase in java

From this I want take the value of email from mailID and subject, title from mailText.i'm able to access the value of single child but when it show null with when try get with all three.
Following code working for single child:
DatabaseReference databaseRef = database.getReference("/");
databaseRef.addValueEventListener(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
ArrayList<String> email = new ArrayList();
for (DataSnapshot sd: dataSnapshot.getChildren()) {
String emailStr = sd.child("email").getValue(String.class);
email.add(emailStr);
System.out.println(email);
}
latch.countDown();
}
Above code gives me array contain the all email like that i want to take value of email,title and subject.

Assuming that the new node is a direct child of your Firebase root, to achieve what you have explained in your comments, please use the following lines of code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference newRef = rootRef.child("new");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.child("mailID").getChildren()) {
String email = ds.child("email").getValue(String.class);
String name = ds.child("name").getValue(String.class);
Log.d("TAG", email + " / " + name);
}
for(DataSnapshot ds : dataSnapshot.child("mailText").getChildren()) {
String title = ds.child("title").getValue(String.class);
String subject = ds.child("subject").getValue(String.class);
Log.d("TAG", title + " / " + subject);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
newRef.addListenerForSingleValueEvent(valueEventListener);
As you see, you need to attach a listener one step higher in your tree hierarchy and to loop throught the children using getChildren() method twice.

You need to change the database structure(there is no join in firebase), to be able to query and get the required data:
new
mailId
email: userx#gmail.com
name:userx
title: test title
Body: test body
Then you will be able to retrieve the required data for the user.
You can also use Queries to be able to get the related data, example:
DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("new");
ref.orderByChild("email").equalTo("userx#gmail.com");