We Keep Coding

Firebase Realtime Database - reading nested data

I am doing a project with firebase, able to save some records on the database, but retrieving it has been an issue for me, I've meddled with other posts from SO but they haven't worked for me. This is how the database looks like (An example):
And my code for retrieving the data:
private void readDataFromDB() {
databaseReference.child("users").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
User user = new User();
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
user.setStrName(//Get the Name of the user);
user.setStrScore(//Get the Score of the user));
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
The User class:
public class User {
String strName, strScore;
public String getStrName() {
return strName;
}
public void setStrName(String strName) {
this.strName = strName;
}
public String getStrScore() {
return strScore;
}
public void setStrScore(String strScore) {
this.strScore = strScore;
}
}
How can I get the name and score from each specific user

In your code, you are setting values, you need to be retrieving values using the getters.
Try the following:
databaseReference.child("users").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
String name = user.getStrName();
String score = user.getStrScore();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
But, first you need to add the values to the database example:
User user = new User();
user.setStrName("my_name");
user.setStrScore("20");
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("users");
ref.push().setValue(user);
Note setValue():
In addition, you can set instances of your own class into this location, provided they satisfy the following constraints:
The class must have a default constructor that takes no arguments
The class must define public getters for the properties to be assigned. Properties without a public getter will be set to their default value when an instance is deserialized
You need to add a default constructor to the POJO class public User(){} and also the field names in the class should match the ones in the database. So change this String strName, strScore; into this String name, score; and generate the getters and setters again.

Instead of creating profile in every node you can use a global profile node, and in that store the profile data with their UID, which would make it easier for you to fetch detail of single user.
-profile
-UID1
-name
-score
-UID2
-name
-score
While retrieving you can use getCurrentUser.getUid() to retrieve data for each user:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
databaseReference.child("users").child("profile").child(uid).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
User user = new User();
user = dataSnapshot.getValue(User.class);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});

Retrieve data from Firebase into an entity

I'm trying to retrieve data from Firebase database to add it to local database.
This code :
database = FirebaseDatabase.getInstance();
myRef = database.getReference();
Query LANGUAGES_REF = myRef.child("languages").orderByChild("id");
LANGUAGES_REF.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
if (dataSnapshot.hasChildren()) {
Iterator<DataSnapshot> iterator = dataSnapshot.getChildren().iterator();
do {
Language language = iterator.next().getValue(Language.class);
languageR.insert(language);
} while (iterator.hasNext());
}
is not working , and I know it's because Language.class is an entity.
Is there a way other than creating a new class with getters and setters and full constructor ... and repeating everything??
The error I got was:
com.google.firebase.database.DatabaseException: Can't convert object
of type java.lang.Long to type
com.android.android.Database.Entities.Language
at this line :
Language language = iterator.next().getValue(Language.class);
Thanks
edit:
firebase database structure
"languages" : {
"LHZ7cAeOdPn-LwHNjIk" : {
"id" : 1,
"langName" : "Russian"
},
"LHZ7cAtXTGBlnWsdQOd" : {
"id" : 2,
"langName" : "French"
},
"LHZ7cAvrRs0rgI-PaJd" : {
"id" : 3,
"langName" : "Turkish"
}
}
language.class
import java.io.Serializable;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
#Entity
public class Language implements Serializable {
#PrimaryKey(autoGenerate = true)
private int id;
private String langName;
public int getId() {
return id;
}
public String getLangName() {
return langName;
}
public Language(String langName) {
this.langName = langName;
}
public void setId(int id) {
this.id = id;
}
}

To solve this, you need to remove the do-while loop because there is no need to iterate using getChildren() method, you can get the data directly from the dataSnapshot object like this:
#Override
public void onChildAdded(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
Language language = dataSnapshot.getValue(Language.class);
languageR.insert(language);
Log.d(TAG, language.getLangName());
}
The output in your logcat will be:
Russian
French
Turkish

Android - Class java.util.Map has generic type parameters, please use GenericTypeIndicator instead

I know there's a lot of similar questions like mine, but I've read and tried everything but still unable to solve this issue. What I am trying to achieve is to populate my listview with the data from the firebase. Im following a tutorial on youtube but Ive added some stuff, timestamp in particular. The error is in my for loop and says :
Class java.util.Map has generic type parameters, please use GenericTypeIndicator instead
This is my database looks like :
My Notes.java
public class Notes {
String noteId;
String noteCategory;
String note;
String rating;
public Map timeStamp;
public Notes(){
}
public Notes(String noteId, String noteCategory, String note, String rating, Map timeStamp) {
this.noteId = noteId;
this.noteCategory = noteCategory;
this.note = note;
this.rating = rating;
this.timeStamp = timeStamp;
}
public String getNoteId() {
return noteId;
}
public String getNoteCategory() {
return noteCategory;
}
public String getNote() {
return note;
}
public String getRating() {
return rating;
}
public Map<String,String> getTimeStamp() { return timeStamp;}
}
And below is my NoteList.java
#Override
protected void onStart() {
super.onStart();
databaseNotes.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
notesList.clear();
for(DataSnapshot noteSnapshot : dataSnapshot.getChildren()){
Notes notes = noteSnapshot.getValue(Notes.class);
notesList.add(notes);
}
NoteList adapter = new NoteList(MyNotes.this, notesList);
listViewNotes.setAdapter(adapter);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Any advice would be greatly appreciated! Thank you in advance.
EDIT : Okay, Ive tried the suggested answer, and after I logged the map it shows my data on the console. However, how do I iterate my map into the listview ?
Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();

From looking at your DB, it looks like you should use int or long type instead of the map type, since your timestamp has a number value

Firebase Database data collection

I am using Firebase database for my project. For the last few days I tried to retrieve data from database but without luck. I tried many tutorials and questions from Stack.. Database looks like this:
Database structure
My user class
I would like to retrieve information and store it in one of the strings..
My code is:
Every time I receive value Null or an Error. I am not sure If I am using correct reference("Users").
Is there is easy way to retrieve users name and store it into the string? Thanks

First you need to have same names for the fields in your database as in your model class. Looking at you model class, there are some things that you need to do. So, I'll provide a correct way to model your class.
public class UserModelClass {
private String name, sureName, date, phoneNumber;
public UserModelClass() {}
public UserModelClass(String name, String sureName, String date, String phoneNumber) {
this.name = name;
this.sureName = sureName;
this.date = date;
this.phoneNumber = phoneNumber;
}
public String getName() {return name;}
public String getSureName() {return sureName;}
public String getDate() {return date;}
public String getPhoneNumber() {return phoneNumber;}
}
In order to make it work, you need to remove all data from the database and add fresh one. There is a workaround when storing users in a Firebase database. Instead of using that that random key provided by the push() method, to use the uid. For that, I recommend you add the data as in the following lines of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
UserModelClass umc = new UserModelClass("Jonas", "Simonaitis", "today", "123456789");
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("users").child(uid);
uidRef.setValue(umc);
To read data, please use the following code:
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
UserModelClass userModelClass = dataSnapshot.getValue(dataSnapshot.class);
String name = userModelClass.getName();
String sureName = userModelClass.getSureName();
String date = userModelClass.getDate();
String phoneNumber = userModelClass.getPhoneNumber();
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
uidRef.addListenerForSingleValueEvent(eventListener);
In one of my tutorials I have explained step by step how to use the model classes when using Firebase.

First you have to do make these declarations:
private DatabaseReference mUserDatabase;
private FirebaseUser mCurrentUser;
in onCreate you need to make smth like this:
mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();
String current_uid = mCurrentUser.getUid();
mUserDatabase =FirebaseDatabase.getInstance().getReference().child("Users")
.child(current_uid);
mUserDatabase.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String name = dataSnapshot.child("uName").getValue().toString();
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Now you have the user name in "name"

First change userInformationActivity class variable names to match names in the database
example : name -> uName
surname -> uSurname
then
private void showData(DataSnapshot dataSnapshot){
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
userInformationActivity user = dataSnapshot.getValue(userInformationActivity.class);
Log.d("user Name is : " + user.uName);
}
}

Firebase data order

I have a class as seen Below:
public class GlobalHighScore {
String name;
int score;
public GlobalHighScore(String name, int score) {
this.name = name;
this.score = score;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
}
And here I try to make a data receiving.
DatabaseReference scoresRef = firebaseDatabase.getReference("Highscores");
scoresRef.child("GlobalHighScore").orderByChild("score").limitToFirst(10);
scoresRef.addValueEventListener(new ValueEventListener() {
#Override public void onDataChange(DataSnapshot dataSnapshot) {
Iterable<DataSnapshot> keys = dataSnapshot.getChildren();
int i = 0;
for (DataSnapshot key : keys) {
if(i == 10)
break;
orderName[i].setText(key.getValue().toString());
i++;
}
}
When I am doing this, key.getValue().toString() returns json formatted String but I want "name" and "score" seperately. Also, my data is not sorted eventhough I make it sorted.
scoresRef.child("GlobalHighScore").orderByChild("score").limitToFirst(10);
I think I having problem here.
Edit: When I order by "score", it gives data according to date.
Last form is
final TextView[] orderScore = {firstscore, secondscore, thirdscore, fourthscore, fifthscore, sixthscore, seventhscore, eightscore, ninthscore, tenthscore};
final TextView[] orderName = {firstname, secondname, thirdname, fourthname, fifthname, sixthname, seventhname, eightname, ninthname, tenthname};
DatabaseReference scoresRef = firebaseDatabase.getReference("Highscores").child("GlobalHighScore");
scoresRef.orderByChild("score").limitToFirst(10);
scoresRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
int i = 0;
for (DataSnapshot data : dataSnapshot.getChildren()) {
if(i == 10)
break;
String name = data.child("name").getValue().toString();
String score = data.child("score").getValue().toString();
orderName[i].setText(name);
orderScore[i].setText(score);
i++;
}
}
It gives no data record at all.

Try this:
DatabaseReference scoresRef = firebaseDatabase.getReference("Highscores").child("GlobalHighScore");
Query q=scoresRef.orderByChild("score").limitToFirst(10);
q.addValueEventListener(new ValueEventListener() {
#Override public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot data : dataSnapshot.getChildren()){
String name=datas.child("name").getValue().toString();
String score=datas.child("score").getValue().toString();
}
}
Since you want the name and the score alone you can do the above, to be able to retrieve them alone.
.orderByChild("score").limitToFirst(10);, using this you will get the first 10, nodes that have the child score.
limitToFirst(10) //to get the first 10 of a specific child
limitToLast(10) //to get the Last 10 of a specific child

When you are using the following line of code:
Iterable<DataSnapshot> keys = dataSnapshot.getChildren();
The childrens that you are getting when iterating are actual objects, not Strings. Using toString() method doesn't make any sense because you cannot cast an Object to a String and expect to get the values within it. That's why you are getting that "json formatted Strings". So what are you getting when iterating are actual maps. So to get the name and score you need to iterate through the map and use: map.get("name"); and map.get("score");.
You don't need to change the entire code, your code is fine. Just solve this minor issue.