Develop Reference

how to get value from firebase node

I want to get the value of isSeen node in Android Studio. The M6F2mJjQ8uGPXAynZzV is an id of the message and change message to message. And I want to get this value in an Adapter class.

So you want to get a boolean, convert to string and compare it to Another string:
If that what you want then this is the answer for you:
//this is the string that you want to compare against
String yourString = "true";
//this is your reference
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("Chats");
//make a listener
ValueEventListener listener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//loop through the random key IDs
for(DataSnapshot ds : dataSnapshot.getChildren()){
//get the boolean "isSeen"
boolean isSeen = ds.child("isSeen").getValue(Boolean.class);
//convert boolean to string
String isSeenString = String.valueOf(isSeen);
//compare isSeenString with your String
if(isSeenString.equals(yourString)){
//they are equal
}else{
//they are not equal
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
};
//add the listener
ref.addValueEventListener(listener);

If you want to get the isSeen value then try the following:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("Chats");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot data: dataSnapshot.getChildren()){
Boolean isSeen = data.child("isSeen").getValue(Boolean.class);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
});
Iterate inside Chats node and then you can retrieve isSeen.

Getting Firebase child key under random key

I want to retrive division and rno from for all key in array and compare those values in array with two other strings. how to do that?

You can get all children. try below code:
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference reference = database.getReference();
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot ds: dataSnapshot.getChildren()) {
String rno = ds.child("rno").getValue().toString();
String div = ds.child("division").getValue().toString();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

I don't understand your question. But you can play on those who fulfill the requirements of the child and fulfill the conditions.
DatabaseReference roomRef = dbRef.child("Everybody Room List Messages");
ValueEventListener roomEventListener = new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot dsKey : dataSnapshot.getChildren()) {
for (DataSnapshot dsNick : dsKey.getChildren()) {
if (dsNick.child("nick").getValue().toString().equals(Nick)) {
dsNick.child("image").getRef().setValue("");
}
}
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
};
roomRef.addListenerForSingleValueEvent(roomEventListener);

UPDATE
So, if I understand, you need this code:
FirebaseDatabase database = FirebaseDatabase.getInstance();
database.getReference().addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot item: dataSnapshot.getChildren()) {
String snapDiv = item.child("division").getValue().toString();
String snapRno = item.child("rno").getValue().toString();
if(snapDiv.equals(divi) && snapRno.equals(roll)){
//Here you can do everythings you need because division and rno value are those you are searching.
}
}
}
});
I can't understand completly your question.
You need to retrieve for each child his division and rno value. After that you need to compare them with other variables. But in the session these variables are 2 and fixed or you need to compare with a list of pairs?
After that, assuming that the above question will be clarify, if strings are matches, you need to update the value of sub1, sub2,...,sub5 fields?
Please, give us more informations to understand your situation and give you more support.

Getting data from Firebase using orderByChild query

I have a String stationName and I want to fetch distance from FireBase according to the stationName I provided.
Here is my Firebase Database:
I am using orderByChild query to filter result and I need fetch only the distance value. Here is my code:
Query query = FirebaseDatabase.getInstance().getReference("Stations").orderByChild("Name").limitToFirst(1).equalTo(sourceName);
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
String distance;
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
distance = dataSnapshot.child("Distance").getValue(String.class);
tt.setText(distance); //to check if it is working or not
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
I need to know what is wrong with code. It's not returning any value.
Thanks in advance

Replace this
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
distance = dataSnapshot.child("Distance").getValue(String.class);
tt.setText(distance); //to check if it is working or not
}
With this
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
distance = snapshot.child("Distance").getValue().toString(); // you
//cannot pass the String.class as in the getValue() parameters becasue a long value
//can not be cast to class object so you need to call toString() method to convert long value
//into the string value.
tt.setText(distance); //to check if it is working or not
}
Hope it helps

Android Firebase, Get position of key in node

I want to get data according to user's ranking. First order by user's points and get users position in node. But I can't think of the way to implement this.
First This is my firebase 'users' node
Maybe It will be like 'databaseRef.child("users").orderByChild("points")...'
I don't know from here.
ps. It's not get nth item. It's 'where is the item' ( item's nth )
Thank you!

This can be done by adding a ctr in you dataSnapshot loop
myRef = FirebaseDatabase.getInstance().getReference().child("users");
final Query query = myRef.orderByChild("points");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
int total = dataSnapshot.getChildrenCount();
int i = 0;
// loop through dataSnapshot
for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
String nickName = childSnapshot.child("nickName").getValue(String.class);
if (nickName.equals(mUser.getNickName()) {
//when nickName would match
int userPlace = total - i;
int points = childSnapshot.child("points").getValue(Interger.class);
//do something here
break;
} else {
i++;
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

Kindly read
Retrieving Data.
How Data is Ordered
The callback function receives a DataSnapshot, which is a snapshot of
the data. A snapshot is a picture of the data at a particular database
reference at a single point in time. Calling val() / getValue() on a
snapshot returns the a language-specific object representation of the
data. If no data exists at the reference's location, the snapshot's
value is null.
If you want to get all points then check this LOGIC.
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("products");
ref.addListenerForSingleValueEvent(
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
ArrayList<Integer> points = new ArrayList<>();
for (Map.Entry<String, Object> entry : products.entrySet()){
Map singleUser = (Map) entry.getValue();
points.add((Integer) singleUser.get("points"));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
//handle databaseError
}
});

I solve this problem. Android_K.Doe's answer is right. I add some code in his code. Because Firebase database does not give descending query.
final Query query = databaseReference.child("users").orderByChild("points");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
int i = 0;
int all = (int) dataSnapshot.getChildrenCount();
Log.d(TAG, "all: " + all);
for (DataSnapshot ds : dataSnapshot.getChildren()) {
String nickName = ds.child("nickName").getValue(String.class);
if (nickName.equals(user.getNickName())) {
Log.d(TAG, "nickName: " + user.getNickName());
int userPlace = i;
Log.d(TAG, "position: " + userPlace);
myInfoRankingNumTxt.setText(Integer.toString(all - (i)) + "위");
break;
} else {
i++;
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

firebase - get single object from list as snapshot

So I have a list of objects stored in firebase and want to query for just one object using child equal to method but I am getting a map with single key value instead.
Code below showing what I want to achieve instead of dealing with hashmaps.
final FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference coutryRef = database.getReference(FireContract.PATH_COUNTRY);
Query countryQuery = coutryRef.orderByChild(FireContract.CHILD_NAME)
.equalTo(TestUtilities.TEST_COUNTRY_ALGERIA).limitToFirst(1);
countryQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Country country = dataSnapshot.getValue(Country.class);
assertEquals(TestUtilities.TEST_COUNTRY_ALGERIA, country.getName());
//get country key
String coutryKey = dataSnapshot.getKey();
}
#Override
public void onCancelled(DatabaseError databaseError) {
fail("Failed to get country: " + databaseError.getMessage());
}
});

When you fire a query, you will always get a list of results. Even when there is only a single item matching the query, the result will be a list of one item.
To handle the list, you can either use a ChildEvenListener or you can loop over the children in your ValueEventListener:
countryQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot countrySnapshot: dataSnapshot.getChildren()) {
Country country = countrySnapshot.getValue(Country.class);
assertEquals(TestUtilities.TEST_COUNTRY_ALGERIA, country.getName());
//get country key
String countryKey = countrySnapshot.getKey();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
fail("Failed to get country: " + databaseError.getMessage());
}
});