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how do i retrieve a nested object from Firebase?

I am trying to retrieve a nested list of workouts from a Realtime Database and I don't know how to do it.
I made some research and still couldn't really figure out how am supposed to do it.
The Realtime Database JSON file looks like this :
I am looking to retrieve data by workout, for example, if someone presses the workout one button I should retrieve the full workout one object. but I don't know how am supposed to design my query request nor how am supposed to structure my model object that conceives the received data.

As I see in your screenshot, under the "Workout one" node, you have two nested levels of data. So to get all exercises for each day, you have to loop over the children twice:
DatabaseReference db = FirebaseDatabase.getInstance().getReference();
DatabaseReference workoutOneRef = db.child("Fat Loss").child("Workout one");
workoutOneRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
#Override
public void onComplete(#NonNull Task<DataSnapshot> task) {
if (task.isSuccessful()) {
for (DataSnapshot daySnapshot : task.getResult().getChildren()) {
for (DataSnapshot exerciseSnapshot : daySnapshot.getChildren()) {
String name = exerciseSnapshot.child("name").getValue(String.class);
Log.d("TAG", name);
}
}
} else {
Log.d("TAG", task.getException().getMessage()); //Never ignore potential errors!
}
}
});
Please also don't forget that the Firebase API is asynchronous. So any code that needs data from the database needs to be inside the onComplete() method, or be called from there. To understand better, I recommend you check the following resource:
How to read data from Firebase Realtime Database using get()?

I think below line code help you.
databaseReference = FirebaseDatabase.getInstance().getReference().child("Fat Loss").child("Workout one").child("day 1")
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
allTaskList.clear();
if (snapshot.exists()) {
for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
//modal class object
AddTODOListModal model = dataSnapshot.getValue(AddTODOListModal.class);
assert model != null;
model.setId(dataSnapshot.getKey());
allTaskList.add(model);
}
adapter = new TODOListAdapter(TODOListHomeActivity.this, allTaskList);
binding.rvTODO.setAdapter(adapter);
}else {
Utils.showToast("No Data Available");
}
Utils.dismissProgressDialog();
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
Utils.showToast(error.getDetails());
}
});
Reference link :- https://firebase.google.com/docs/database/android/lists-of-data

How to parse all child fields and find what I need in Firebase Database?

I do password recovery and I need to know if there is a user in the database with the entered E-mail'om. How do I do that? Here is the structure:
For example, the user entered E-mail - goshan164#gmail.com and I need to know if there is such a mail in my database. And if it exists, then find out the uID of the user with such mail. How do I do that?
P.S uId initially I do not know. In the picture uId = zKCTYc1JkROrGxgOZgvm9CvfSU42

You're looking for a Firebase database query, in this case one that compares the child property of each node against the value you're looking for:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("users"); // or whatever your node is
Query query = ref.orderByChild("account").equalTo("goshan164#gmail.com");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) {
System.out.println(userSnapshot.getKey());
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}
For more on this, see the Firebase documentation on ordering an filtering data.

Fetch a data in Firebase using another data

This is the Firebase database structure of my project.
I want to fetch complaint division, describe, stat for the particular hostelname and roomno. How to fetch these data and display in android project?

To get all those values, please use the following lines of code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference complaintsRef = rootRef.child("Complaints");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String complaintDivision = ds.child("complaintdivision").getValue(String.class);
//Get the other properties in the same way
Log.d(TAG, complaintDivision);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
complaintsRef.addListenerForSingleValueEvent(valueEventListener);
The output in your logcat will be:
Plumber Related

This is a basic function in Firebase on Android. You can use ValueEventListeners with the database reference to do this.
The steps to achieve the desired results can be enlisted as below:
Create a Complaint model with the same fields as your database.
Get the right Firebase reference for your database node and add a ValueEventListener instance to listen for database changes.
Pass a DataSnapshot into the Complaint class and assign it to a Complaint object.
Do what you want with the Complaint object you have obtained.
Creating a Complaint class:
class Complaint {
// your fields should have the same name as database fields to prevent unnecessary complications
public String complaintdivision;
public String complaintid;
public String describe;
public String hostelname;
public String roomno;
public String stat;
public Complaint(){// required for Firebase
}
}
Getting the data from Firebase:
ArrayList<Complaint> myComplaintArrayList = new ArrayList<>();
FirebaseDatabase.getInstance().getReference().child("Complaints").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for(DataSnapshot complaint: dataSnapshot.getChildren()){
Complaint c = complaint.getValue(Complaint.class);
myComplaintArrayList.add(c);// you should have an ArrayList<Complaint> for this loop
}
// do what you want with the items you obtained
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException();
}
});
This is pretty much all of it. If you are still having problems, you should read a tutorial on Firebase.

So to fetch the data you would first declare a Firebase DatabaseReference object that points to your database:
private DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
You would then write a query using this object:
Query query = mDatabase.child("Complaints");
Now you attach a SingleValueEventListener to this query:
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Write a for-each loop to cycle through your node's children
for(DataSnapshot data: dataSnapshot.getChildren()){
//Create an instance of your model class to
//store the received data
//Make sure you have an empty constructor in your model class
Complaint complaint = data.getValue(Complaint.class);
//then simply call your getters on the complaint object
//to get what you need
complaint.getComplaintDivision();
complaint.getDescription();
//...
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
To fetch more specifically, you just modify the query.
For more information on queries, see this

FirebaseDatabase Query : How to query some data basing on some values from other childs. For FirebaseRecyclerAdapter

I'm working on my app that has a fragment, this fragment displays new users with a follow button using this query :
query = mDatabaseref.child("users").orderByChild("date").limitToLast(10);
After a follow button is clicked, the current User Uid gets saved as a child in the other child that has a name "Follows" with 2 other child's "following" and "followers" as it showed in the below picture :
what I want to do is to make a Query for an other fragment with the name Following and show all the users that the Current user is following with the ability of getting their names, I was thinking of making a data dataSnapshot in the FirebaseRecyclerAdapter onBindViewHolder method basing on the Uid tooken from the childs, but I think it's gonna be complex, on the other hand, i tried to sort the follows in the user Info child direclty, but it leads to a strange behaviour on the RecyclerView.

I'm not going to write you all the code including your FirebaseRecyclerAdapter, I will show you just how to query to get the desired results. As i understand, here is the problem. So in order to achieve this, you need to query your database twice, once to get all those ids and second, based on those ids to get the names. So, please use the following code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference followingRef = rootRef.child("follows").child(uid).child("following");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String userId = ds.getKey();
DatabaseReference userIdRef = rootRef.child("users").child(userId);
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot dSnapshot : dataSnapshot.getChildren()) {
String name = dSnapshot.child("name").getValue(String.class);
Log.d("TAG", name);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
userIdRef.addListenerForSingleValueEvent(eventListener);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
followingRef.addListenerForSingleValueEvent(valueEventListener);
The result in your logcat will be all the names of the followers that belong to a single user.

Google firebase check if child exists

In my app, I need to check if a given element of my database on firebase has a child with a given name. I hoped it could be done by using something along the lines of:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
if (rootRef.childExists("name")) {
//run some code
}
I searched but I couldn't find anything useful.

Edit 2; worth putting on top: I think it is worth mentioning that this is actually downloading all data at this snapshot just to check whether any data exists. You should be mindful here. If the reference is huge (e.g. actually the root reference and not a specific child/property) then you should either find a deeper node you can use to check for existence or design your data structure differently so an efficient check is possible.
A database reference is effectively the URL for that data. You want to actually get data to see whether a child exists. This is why the method you seem to be looking for is on DataSnapshot.
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
void onDataChange(DataSnapshot snapshot) {
if (snapshot.hasChild("name")) {
// run some code
}
}
});
Now, this design pattern feels a bit strange. You're reading the whole database just to see whether "name" exists. You can make this a bit more efficient by listening to rootRef.child("name") and then just checking whether snapshot.exists().
If you're trying to do validation here, and not control flow, you should consider putting this code in your rules.json.
edit: I originally used the wrong function name (childExists instead of hasChild)

Don't do like this
NEVER
It will take all your data and bring to device
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
void onDataChange(DataSnapshot snapshot) {
if (snapshot.hasChild("name")) {
// run some code
}
}
});
Check it by this way.
It will return the value of the child if exists, otherwise -> null
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.child("childName")
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
void onDataChange(DataSnapshot snapshot) {
if (snapshot.getValue() == null) {
// The child doesn't exist
}
}
});

A complete solution. No need to download all the data. Just check if the child exist like this:
// Assuming the names are in the name node. Remove "name/" if not
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference("name/" + name);
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.exists()) {
// Exist! Do whatever.
} else {
// Don't exist! Do something.
}
}
#Override
public void onCancelled(DatabaseError error) {
// Failed, how to handle?
}
});

Try using .childexists in combination with .equalTo("Your specific name")

UsersRef = FirebaseDatabase.getInstance().getReference();
Users.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.hasChild("childName")) {
// it exists!
}else{
// does not exist
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});

Use snapshot.exists() to check if the referenced database entry contains a child , irrespective of the value of the child.