Develop Reference

How can I fetch certain type of data from Firebase Realtime Database?

I know that there is a lot of code on this, but I can't find the solution for my problem.
I have a realtime database :
I have to fetch "saluteBossMassima:"
The way I have declared and initialized my variables:
DatabaseReference databaseMonster;
String id;
databaseMonster=FirebaseDatabase.getInstance().getReference("monster");
id = databaseMonster.push().getKey();
The code that I try:
databaseMonster.child(id).addValueEventListener(newValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String saluteMassimaBossDB = dataSnapshot.child("monster").child("saluteBossMassima").getValue().toString();
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
}
});
Anyone can help me?

This won't work:
databaseMonster=FirebaseDatabase.getInstance().getReference("monster");
id = databaseMonster.push().getKey();
When you call push() it generates a new unique key for writing to. There is zero chance that this is the same as the existing key in your screenshot.
If you already know the key of the node you want to read, you should pass that key to child():
// 👇 specify key here
databaseMonster.child("-MtcylP327pK9pUQB54").addValueEventListener(newValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String saluteMassimaBossDB = dataSnapshot.child("saluteBossMassima").getValue(String.class);
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
throw error.toException(); // 👈 never ignore errors
}
});
If you know some value of the node(s) you want to read, but not the key, you can use a query to find the nodes:
// 👇 Use a query to select the nodes with a specific value
Query query = databaseMonster.orderByChild("dannoAttaccoCaricato").equalTo(300);
query.addValueEventListener(newValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// 👇 Loop over the results, since there may be multiple
for (DataSnapshot monsterSnapshot: dataSnapshot.getChildren()) {
String id = monsterSnapshot.getKey();
String saluteMassimaBossDB = monsterSnapshot.child("saluteBossMassima").getValue(String.class);
}
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
throw error.toException();
}
});
Now we need to loop over dataSnapshot.getChildren(), since there may be multiple nodes with the value of 300 for dannoAttaccoCaricato.
If you know nothing about the node, the best you can do is read all of them and loop over the results:
// 👇 Read all nodes under /monster
databaseMonster.addValueEventListener(newValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot monsterSnapshot: dataSnapshot.getChildren()) {
String id = monsterSnapshot.getKey();
String saluteMassimaBossDB = monsterSnapshot.child("saluteBossMassima").getValue(String.class);
}
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
throw error.toException();
}
});

How to check if a value exists already in a Firebase and get key in android

In my android application, when the user logs in, I need to check my realtime database to determine if the users ID exists within this database. Once the users ID has been located, i then need to retrieve the parent node of this ID in order to determine if the user logging in is a customer or employee. I'm having some difficulties coding this, as i'm relatively new to using firebase.
Here is my code so far:
final String user_id = Objects.requireNonNull(firebaseAuth.getCurrentUser()).getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
ValueEventListener eventListener = new ValueEventListener()
{
#Override
public void onDataChange(DataSnapshot dataSnapshot)
{
for(DataSnapshot ds : dataSnapshot.getChildren())
{
if(ds.child(user_id).exists())
{
//check if employee or customer?
String cust_or_emp = ds.child(user_id).getKey();
Log.d("test1",String.valueOf(ds.child(user_id).getKey()));
if (cust_or_emp.equals("Customers"))
{
name= Objects.requireNonNull(ds.child(user_id).child("User_Information").child("firstName").getValue()).toString();
Log.e("first name is ", "firstname :" + name);
toNextActivity = new Intent(getActivity(), MainActivity.class);
toNextActivity.putExtra("name",name);
Log.e("2first name is ", "firstname :" + name);
progressBarLayout2.setVisibility(View.GONE);
Objects.requireNonNull(getActivity()).getWindow().clearFlags(WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE);
Objects.requireNonNull(getActivity()).startActivity(toNextActivity);
getActivity().finish();
} else if (cust_or_emp.equals("Employee")) {
//code for if the key is employee
}
}
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError)
{
Log.d("error", databaseError.getMessage()); //Don't ignore errors!
}
};
rootRef.addListenerForSingleValueEvent(eventListener);
Currently when I run my application, nothing appears to happen.

You're attaching a value listener to the root of your database. Then in your onDataChange you loop over the child node, which means that your ds snapshot is for the Users node, while you seem to think it's for the Employee and Customers node.
The fix should be to listen to the Users node instead:
rootRef.child("Users").addListenerForSingleValueEvent(eventListener);
Your current approach is highly inefficient, as (even when you fix the above) you're loading the entire Users node to check if a specific user exists in there. As you add more users to the app, this means you're loading more and more data, without using it.
A better approach is to check whether the specific user exists under each specific node:
rootRef.child("Users/Employee").child(user_id).addListenerForSingleValueEvent(new new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
... handle the Employee
}
else {
rootRef.child("Users/Customer").child(user_id).addListenerForSingleValueEvent(new new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
... handle the Customer
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}

Firebase OrderByChild() and EqualTo() is not working properly

I need to find the existing Child inside the Random Key and I have used OrderByChild() and EqualTo() to filter the queries but it behaves soo weird that for sometimes it showing child exists for only one Child and for sometimes it doesnot work.
i need to check for the child (date_expense) of "February_2019" exist or not? i've tried this
MainActivity
databaseReference = firebaseDatabase.getReference("Expenses_Details");
expensesaddref = databaseReference.child(username).child("Expense_Month").child(monthyr);
int currentInt=Integer.parseInt(currentdate);
numberToWord((currentInt % 100));
Log.d("date_string",String.valueOf(dateString));
final String date_expense=expensesname +"" + dateString;
final ExpenseClass expenses=new ExpenseClass(expensesname,currentdate,date_expense,totalcost);
expensesaddref.orderByChild("date_expense").equalTo(date_expense).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Toast.makeText(getContext(), "Expense Already exists!!", Toast.LENGTH_SHORT).show();
}
else {
String key = expensesaddref.push().getKey();
expensesaddref.child(key).setValue(expenses);
showListAdd(expensesname);
Log.d("Adding", "Data Adding");
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
}}
Note
if child exist already in db then it should display toast but expense is again adding even though the child is already db
In the Program,
monthYr is February_2019
Currentdate is date of the present day
dateString is date in words(ie one,Eleven,Twenty)
This is the Firebase structure what Iam getting .date_expense is adding even though child is exist already

i have found that the below code working as per my need
ValueEventListener valueEventListener=new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
boolean isTitleAlreadyUsed = false;
for (DataSnapshot ds: dataSnapshot.getChildren()) {
if (ds.hasChild("date_expense") && (expDate.equals(ds.child("date_expense").getValue()))) {
isTitleAlreadyUsed = true;
}
}
if(isTitleAlreadyUsed){
Toast.makeText(getContext(),"Exist",Toast.LENGTH_SHORT).show();
}else
{
String key=expensesaddref.push().getKey();
expensesaddref.child(key).setValue(expenseClass);
showListAdd(lower_exp);
Toast.makeText(getContext(),"Added",Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
};
expensesaddref.addListenerForSingleValueEvent(valueEventListener);

Fetch and Compare Key and Value from Firebase Realtime Database

I'm trying to make an app in which user store his Data. I've used user shared preferences to save user login details but still for security purpose, i made an activity(Verify Passcode Activity) that ask user Passcode to allow access on the data. Now i'm able to save, fetch and delete data. But in my Verify Passcode Activity, i just want to fetch that particular key and value where passcode is stored. I don't want to fetch complete data in Verify Passcode Activity.
Below is the code which i used to save passcode to database:-
databaseReference.child(uniqueID).setValue(passcode);
Below is the code i'm tried to fetch only passcode:-
dbreference.child(uniqueID).orderByChild("passcode").equalTo(pass).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()){
Toast.makeText(getApplicationContext(), "Data exist", Toast.LENGTH_LONG).show();
}else{
Toast.makeText(getApplicationContext(), "Data doesn't exist", Toast.LENGTH_LONG).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
Here uniqueID is "abhishek88666kumar"and pass is a variable used for getText().
Here is the screenshot of my Firebase Database :-
Database Screenshot
Here is Verify Passcode Activity Screenshot:-
Please have a look at Database Screenshot and Verify Passcode Activity Screenshot.
Agenda:
getText() from textView inside activity.
getValue from firebase realtime database (only for current user. 'abhishek88666kumar' in our case).
compare if 1 and 2 are same or not. (If same then redirect to MainActivity else show error.)
Please tell me what i'm doing wrong.

Thanks to all for your help :) Your answer didn't worked for me but with the help of your answers and my few knowledge, I made a solution for my problem myself.
Here is the code that matches my requirement. This code is working exactly how I wanted.
dbreference = FirebaseDatabase.getInstance().getReference("passcodes");
Query query = dbreference.orderByKey().equalTo(currentUser); //current user is "abhishek88666kumar" in this case.
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()){
String passcode = txtPasscode.getText().toString;//Passcode is 1234 in this case.
String fetchedValue = "";
for (DataSnapshot snap : dataSnapshot.getChildren()){
fetchedValue = (String) snap.getValue();
}
if (!passcode.equals(fetchedValue)){
Toast.makeText(getApplicationContext(), "Passcode doesn't match.", Toast.LENGTH_LONG).show();
}else{
Toast.makeText(getApplicationContext(), "Passcode matched.", Toast.LENGTH_LONG).show();
}
}else{
Toast.makeText(getApplicationContext(), "No passcode found for this user", Toast.LENGTH_LONG).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});

Assuming pass is a value like 1234, this line:
dbreference.child(uniqueID).orderByChild("passcode").equalTo(pass).addListenerForSingleValueEvent(...
Should be:
FirebaseDatabase.getInstance().getReference("passcodes").orderByValue().equalTo(pass).addListenerForSingleValueEvent(...
This way the DataSnapshot will contain all child nodes of passcodes that have the value 1234, i.e. "abhishek88666kumar" in your JSON sample.
Also be sure to study the documentation on sorting and filtering data.

This is the first way to compare firebase data.
btnSave.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
passcode = editText.getText().toString();
Toast.makeText(getApplicationContext(), "Data :"+passcode, Toast.LENGTH_LONG).show();
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("passcode");
Query applesQuery = ref.orderByValue().equalTo(passcode);
applesQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()){
Toast.makeText(getApplicationContext(), "Data exist", Toast.LENGTH_LONG).show();
}else{
Toast.makeText(getApplicationContext(), "Data doesn't exist"+passcode, Toast.LENGTH_LONG).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Log.e(TAG, "onCancelled", databaseError.toException());
}
});
}
});
This is the second way to compare firebase data.
btnSave.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
check = editText.getText().toString();
Toast.makeText(getApplicationContext(), "Data :"+check, Toast.LENGTH_LONG).show();
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("passcode");
// Query applesQuery = ref.child("Customers").orderByChild("abhishek88666kumar").equalTo(passcode);
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();
if(map.get("abhishek88666kumar")!=null){
passcode = map.get("abhishek88666kumar").toString();
if (passcode.equals(check))
{
Toast.makeText(getApplicationContext(), "Data exist", Toast.LENGTH_LONG).show();
}
else{
Toast.makeText(getApplicationContext(), "Data doesn't exist"+check, Toast.LENGTH_LONG).show();
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Log.e(TAG, "onCancelled", databaseError.toException());
}
});
}
});
Both are working.
Hope it's help full for you.
thank you.

How to share Firebase data with two different apps

I've successfully inserted data into my firebase database.(Client App).
Now all I have to do is to retrieve data back into a text view but in a different application.(Admin Application).
public void clients()
{
String name="Abch";
String gender="Abcg";
String barber="Abcf";
String concern="Abce";
String dt="Abcd";
if(!TextUtils.isEmpty(name) || !TextUtils.isEmpty(gender) || !TextUtils.isEmpty(barber) || !TextUtils.isEmpty(concern) || !TextUtils.isEmpty(dt))
{
String id=databaseReference.push().getKey();
client client=new client(id,name,gender,barber,concern,dt);
databaseReference.child(id).setValue(client);
Toast.makeText(this, "", Toast.LENGTH_SHORT).show();
}
else
{
Toast.makeText(this, "Something Went Wrong Please Check Again", Toast.LENGTH_SHORT).show();
}
}

If you want to retrieve the data in another application, you have to use eventListeners, provided you have set the rules of your database right.
There are three eventListeners you can use namely, singleValueEventListener, valueEventListener and childEventListener. Since you have not posted the structure of your database, I'm assuming you know how to get the required DatabaseReference.
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
Client client = ds.getValue(Client.class);
}
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
};
databaseReference.addListenerForSingleValueEvent(eventListener);