Develop Reference

Is it possible to save data with multiple keys in Android Firebase realtime database

I am studying Android and Firebase by myself.
I'm have a problem with storing user information and creating login and user registration functions by linking Android and Firebase.
When saving user information in Firebase, is only one key possible? I want to save more keys.
I tried changing main key, but it's failed.
Sorry. I can't speak English. I'm using a translator now.
enter image description here
I saved user information like in the picture, but there was a problem during the production of the ID search function.
private FirebaseDatabase database = FirebaseDatabase.getInstance(); //파이어베이스 데이터베이스 연동
DatabaseReference databaseReference = database.getReference();
DatabaseReference conditionRef = databaseReference.child("User");
conditionRef.child(userID).child("userID").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
String userid = snapshot.getValue().toString();
if(snapshot.exists()){
Toast.makeText(getApplicationContext(), "아이디: " + userid, Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getApplicationContext(), "등록되지 않은 회원입니다.", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
}
});
The code is as above.
However, because "conditionRef.child(userID)" does not have a userID value, the information cannot be retrieved from Firebase.

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...

Firebase get reference by value

I have Firebase node that look like this
How can i make a condition if (name.equalsTo("someValue") to scan database inside campus and get reference to node with key? I this case, i want to get reference or key of kazjap

To find the node under /campus/building where name has a certain value, you can use a query like this:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("campus/building");
Query query = ref.orderByChild("name").equalTo("someValue");
And then read the results of the query with:
query.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
#Override
public void onComplete(#NonNull Task<DataSnapshot> task) {
if (!task.isSuccessful()) {
Log.e("firebase", "Error getting data", task.getException());
}
else {
for (DataSnapshot childSnapshot: task.getResult().getChildren()) {
Log.d("firebase", String.valueOf(childSnapshot.getKey()));
}
}
}
});
Or:
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
// Handle the data
Log.d("TAG", childSnapshot.getKey())
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Getting User failed, log a message
Log.w("firebase", "Error getting data", databaseError.toException());
// ...
}
});
Firebase queries only work on direct child nodes, so this only works if you know the /campus/building part of the path already. There is no way to search across the entire campus for a building by its name in any campus. For more on that, see Firebase Query Double Nested

SingleValueEvent Showing null

Query sqlite = mDatabaseReference.child("Messages").child(MessageSenderId).child(MessageRecieverId);
sqlite.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild("Message")) {
String msg = dataSnapshot.child("Message").getValue().toString();
String from = dataSnapshot.child("From").getValue().toString();
String time = dataSnapshot.child("Time").getValue().toString();
} else {
Toast.makeText(getApplicationContext(), "NULLLL", Toast.LENGTH_SHORT).show();
}
Database
This is the most basic thing in the database. I have never got a problem with childEvent or valueEvent and i want a single event for now and I'm not able to fetch.
There is no error because i have put an if statement and it shows toast as null which means dataSnapshot doesn't have a child named messages but it's right there. I tried putting a for loop too, but didn't work

You have not given the full reference. There is a list of push keys and you have to use a foreach loop.
Query sqlite = mDatabaseReference.child("Messages").child(MessageSenderId).child(MessageRecieverId);
sqlite.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot vinSnapshot : dataSnapshot.getChildren()) {
if (vinSnapshot .hasChild("Message")) {
String msg = dataSnapshot.child("Message").getValue().toString();
String from = dataSnapshot.child("From").getValue().toString();
String time = dataSnapshot.child("Time").getValue().toString();
} else {
Toast.makeText(getApplicationContext(), "NULLLL", Toast.LENGTH_SHORT).show();
}
}
Or you can store all data into ArrayList then perform your task.

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");