I've been trying to retrieve an element from my Firebase database using its key. I have a class User and users are present in database.
I want to retrieve an object user using its key with this method :
public User getConnectedUserByUId(final String uid){
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users");
final List<User> connectedUser= new ArrayList<User>();
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot item: dataSnapshot.getChildren()) {
if (item.getKey()==uid)
{
User user= dataSnapshot.getValue(User.class);
connectedUser.add(user);
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return connectedUser.get(0);
}
but it returns an empty list every time.
The issue is here:
if (item.getKey()==uid)
since you are comparing 2 String in java you have to use the method
string.equals(Object other) not the == operator.
Moreover, since you know the key of the data in Firebase you can use it to get the reference without cycling all children.
Something like:
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users").child(uid);
Here you try to check a very specific ID only on changed data. Instead, try using a Firebase Query with filterByKey and not using your own function to achieve that. Here's sample code that I would use to try to replace your function:
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users");
Query connectedUser = ref.equalTo(uid);
connectedUser.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
// TODO: handle the post here
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Getting Post failed, log a message
Log.w(TAG, "loadPost:onCancelled", databaseError.toException());
// ...
}
});
As specified in the Firebase documentation here: https://firebase.google.com/docs/database/android/lists-of-data#filtering_data
in the line : User user= dataSnapshot.getValue(User.class);
you have to put : User user= item.getValue(User.class);
and you have to check the id after you get the user:
if (user.getKey()==uid){
connectedUser.add(user);
}
There are 2 mistakes and a minor issue:
you are using == to compare two String objects. In java, this is true only if they are the same reference. Use equals instead.
addValueEventListener only adds a listener that gets invoked once after you add it and then every time something changes in the value you are listening to: this is an asynchronous behaviour. You are trying to get data synchronously instead. Please read something about this.
you are fetching useless data: you only need an object but you are fetching tons of them. Please consider to use the closest reference you can to the data you are fetching.
So, in conclusion, here's some code. I'd like to point out right now that forcing synchronous acquisition of naturaly asynchronous data is a bad practice. Nevertheless, here's a solution:
public User getConnectedUserByUId(final String uid){
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users").child(uid);
Semaphore sem = new Semaphore(0);
User[] array = new User[1];
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot item: dataSnapshot.getChildren()) {
if (item.getKey()==uid)
{
User user= dataSnapshot.getValue(User.class);
array[0] = user;
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
try
{
sem.tryAcquire(10, TimeUnit.SECONDS);
}
catch (Exception ignored)
{
}
return array[0];
}
EDIT: I've just seen that this post is very old. I'm not sure how I ended up here.
Related
I am trying to retrieve a list that is on a child that starts with something. Below is a sample of data in my Firebase realtime database:
In the image, I want to retrieve all data that starts with the keyword "jsonmat".
I am using thee code below but it always return null:
DatabaseReference db = FirebaseDatabase.getInstance().getReference()
.child("Events");
db.startAt("jsonmat").addListenerForSingleValueEvent(
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Log.i("events", dataSnapshot.toString());
for (DataSnapshot data : dataSnapshot.getChildren()) {
// here the user will have the specified email only
}
}
#Override
public void onCancelled(DatabaseError databaseError){
Log.i("MyApp", "getUser:onCancelled", databaseError.toException());
}
});
What you're trying to do isn't possible. You can't order/filter of a nested key, only on direct child keys (-M...) and on nested values (active: true).
Typically you'll want to create a new top-level node, where you store the keys you're searching for, and then the push keys for each matching nested node:
"category_things": {
"jsonmat_jsonmat": {
"-M62....uYgB": true,
"-M62....2-eO": true
}
}
Also see:
Firebase Query Double Nested
My original, but wrong answer is below...
If you use startAt without specifying an orderBy... clause, the data will be ordered by priority. This priority is a left-over from before Firebase supported ordering on specific properties, so mostly it means that you must call an orderBy... method before filtering.
So:
DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("Events");
db.orderByKey().startAt("jsonmat").addListenerForSingleValueEvent(new ValueEventListener() {
...
What you can do for your case, is to loop 2 times over the children of the node Events:
//the reference to the node Events
DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("Events");
db.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//loop 1
for (DataSnapshot data : dataSnapshot.getChildren()) {
//loop2
for (DataSnapshot dataTwo : data.getChildren()) {
//get the key
String key = dataTwo.getKey();
if(key.startsWith("jsonmat")){
//we got a matching key so extract the data and maybe put them in a list
boolean active = dataTwo.child("active").getValue(Boolean.class);
int bet = dataTwo.child("bet").getValue(Integer.class);
String challenger = dataTwo.child("challenger").getValue(String.class);
String competitor = dataTwo.child("competitor").getValue(String.class);
String game = dataTwo.child("game").getValue(String.class);
............
............
............
}else{
//we didn't get a match
}
}//end loop2
}//end loop1
}
#Override
public void onCancelled(DatabaseError databaseError){
Log.i("MyApp", "getUser:onCancelled", databaseError.toException());
}
});
I want to retrieve data from my database. For example: I just want to get the username and password from my database, what should I implement next ?
public void loginToSystem(String usernameLogin, String passwordLogin){
usernameLogin = username.getText().toString();
passwordLogin = password.getText().toString();
if(TextUtils.isEmpty(usernameLogin)){
username.setError("Please Input Username");
return;
}
else if(TextUtils.isEmpty(passwordLogin)){
password.setError("Please Input Password");
return;
}
else {
Query query1 = databaseReference.orderByChild("usnername").equalTo(usernameLogin);
Query query2 = databaseReference.orderByChild("password").equalTo(passwordLogin);
//What Should I do Here
}
}
What should I do with the Code.
Ps: I am using the DatabaseReference and am I doing a good way to proceed Login with using this ?
Or I have to separate my data username and password using FireAuth
And Personal Data using Firebase Database
You need to add ValueEventListener to be able to retrieve the data:
Query query1 = databaseReference.orderByChild("username").equalTo(usernameLogin);
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
String address=datas.child("address").getValue().toString();
}
}
#Override
public void onCancelled(DatabaseError error) {
}
});
Also you can only use one orderByChild with each listener.
You dont need to add the password in the database as it is stored in the firebase auth. Also you are using a random id generated by push(). Since you are using Firebase Auth, then get the userid and add the data inside of it.
FirebaseUser user=FirebaseAuth.getInstance().getCurrentUser();
String userid=user.getUid();
then you will have:
Users
userid
address: address_here
name: name_here
email:email_here
What you could do is when the user clicks on the login button you could add a ValueEventListener on the node that you want to listen then what you'll get is the whole data from the node and then we could check that if the username and password are contained in the node then you could log in or maybe save the data whichever suits your case.
I have tried the same logic by clicking on a login button and it worked for me. Kindly try the below code.
DatabaseReference ref = mDatabaseReference.child("YOUR NODE NAME");
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()){
HashMap<String,String> map = (HashMap<String,String>)dataSnapshot1.getValue();
if (map.get("username").equals("USERNAME THAT TO BE CHECKED")){
Log.d("Testing","True "+map.get("name"));
}
else {
Log.d("Testing","True "+map.get("name"));
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Hope it works.
I have users on my Application and I store additional information about them in Firebase Database. I need to retrieve additional information in more than one Activity. I do not want to use ValueEventListeners because they are not called unless there is any change in the database. How can I get information about users from Database without using ValueEventListeners?
In my ProfileFragment I need to get name and departmant values.
I get current user from Firebase and I tried to take other information with a function.
talker = new DatabaseTalk();
FirebaseUser currentUser = mAuth.getCurrentUser();
// Get info of logged in user with talker.
loggedInUser = talker.getUserFromID(currentUser.getUid());
This is my DatabaseTalker class to handle read and write operations to database
public class DatabaseTalk {
private FirebaseDatabase mDatabase;
private DatabaseReference UserRef;
private DatabaseReference SurveyRef;
private List<User> userList;
public DatabaseTalk(){
mDatabase = FirebaseDatabase.getInstance();
UserRef = mDatabase.getReference("users");
UserRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot child: dataSnapshot.getChildren()){
userList.add(child.getValue(User.class));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Log.w("Error", "Failed to read value.", databaseError.toException());
}
});
SurveyRef = mDatabase.getReference("surveys");
}
public void WriteUser(User usr){
UserRef.child(usr.getUserID()).setValue(usr);
}
public void WriteSurvey(Survey survey){SurveyRef.push().setValue(survey);}
public User getUserFromID(String id){
for(User usr: userList){
if(usr.getUserID().equals(id))
return usr;
}
return null;
}
}
I think, I can take additional information about users from userList in DatabaseTalk but userList is null always.
EDIT
I changed getUserFromID method. OnDataChange() does not work when I called getUserFromID method.
public User getUserFromID(String id){
DatabaseReference newRef = mDatabase.getReference("users");
DatabaseReference ds = newRef.child(id);
ds.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
userList.add(dataSnapshot.getValue(User.class));
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return userList.get(0);
}
I solved the problem. It turned out I do not know how Firebase works actually. Since onDataChange() make async calls, writing Listener definitions on a function is useless because onDataChange mostly does not trigger before function terminates and this cause function to return null value.
I make the definition of ValueEventListeners in onCreate methods. It triggers now after few seconds my ProfileFragment created. I think it is better to use Progress Dialogs to wait.
Thanks to everyone who interested in the question.
I am storing user details 'firstname' and 'lastname' in UserNode. But when i want to retrieve that details then no data is being retrieved. I tried almost all solutions on the internet but nothing solved my problem. Here is my code for retrieving data of the current user:
FirebaseUser userr = FirebaseAuth.getInstance().getCurrentUser();
if (userr != null) {
String name = userr.getDisplayName();
Log.e("value", name);
}
but it says "println needs a message"
I also tried with this but nothing happened:
DatabaseReference DataRef;
DataRef = FirebaseDatabase.getInstance().getReference().child("UserNode");
DataRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String acctname = (String)dataSnapshot.child("firstname").getValue();
Log.e("name", acctname);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
]1
Please help me I am stuck with it
You're reading a collection of user with a ValueEventListener. As the [Firebase documentation for reading lists with a value event](Listen for value events) explains:
While using a ChildEventListener is the recommended way to read lists of data, there are situations where attaching a ValueEventListener to a list reference is useful.
Attaching a ValueEventListener to a list of data will return the entire list of data as a single DataSnapshot, which you can then loop over to access individual children.
Even when there is only a single [child node], the snapshot is still a list; it just contains a single item. To access the item, you need to loop over the result.
So in your code:
DatabaseReference DataRef;
DataRef = FirebaseDatabase.getInstance().getReference().child("UserNode");
DataRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
String acctname = (String)childSnapshot.child("firstname").getValue();
Log.i("name", acctname);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
Using FirebaseUser:
FirebaseUser implements UserInfo and in UserInfo's getDisplayName() documentation says
Returns the user's display name, if available.
So, it is possible that FirebaseUser.getDisplayName() return null when display name is not set. In that case Log.e() receives null as message and therefore prints println needs a message
Using your own structure:
Instead of using type conversion use getValue(Class<T>) like so:
String acctname = dataSnapshot.child("firstname").getValue(String.class);
Please, read how to retrieve data from firebase. I think you have a problem because you don't have Class Model.
Your steps:
Create model UserModel with firstname and lastname field
Use listener (example from docs):
// Attach a listener to read the data at our posts reference
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Post post = dataSnapshot.getValue(Post.class);
System.out.println(post);
}
#Override
public void onCancelled(DatabaseError databaseError) {
System.out.println("The read failed: " + databaseError.getCode());
}
});
See other answers: How to retrieve data from one single userID Firebase Android and retrieving data from firebase android
I have the following database structure:
I need to delete a child (both key and value), for example, the first one, by knowing his value: xzFD1RahhZYr05nZljIW9BRzvSq1
So I have
String itemToDelete = "xzFD1RahhZYr05nZljIW9BRzvSq1";
FirebaseDatabase database = FirebaseDatabase.getInstance();
databaseReference deleteRef=database.getReference("richieste").child(FirebaseAuth.getInstance().getCurrentUser().getUid());
deleteRef.orderByValue().equalTo(itemToDelete);
deleteRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//What to do with .removeValue(); ?
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
}
I don't know exactly what to do with dataSnapshot to remove the child
Thank you for the answer
Bonus question: what should I do with onCancelled event?
To get the DatabaseReference, you can call DataSnapshot.getReF(), and then you can remove the value by calling .removeValue().
But based on your case, you should iterate the DataSnapshot or use ChildEventListener to make sure you are removing the child and not the whole data under richieste/<user_id>.
To iterate and remove the value:
for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
childSnapshot.getRef().removeValue();
}
There's another error in your code, you should store the reference of this line deleteRef.orderByValue().equalTo(itemToDelete); to another DatabaseReference before attaching the event listener or you can directly attach the listener with this trick deleteRef.orderByValue().equalTo(itemToDelete).addListenerForSingleValueEvent(...);
For the bonus question, the onCancelled will be called if there's an error reading the database such as network or permission problem.
Hope this helps :)
Willik's answer covers the important issues. The code below implements them all.
Update for Comments:
Query is a class in the Firebase SDK. You should be able to import it:
import com.google.firebase.database.Query;
If dataSnapshot.exists() is false, it means there is no data in the database at /richieste/$uid. Check that the UID of the signed-in user is what you expect and there is data for that UID in your database.
String itemToDelete = "xzFD1RahhZYr05nZljIW9BRzvSq1";
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference deleteRef = database.getReference("richieste")
.child(FirebaseAuth.getInstance().getCurrentUser().getUid());
// orderByValue() and equalTo() return a query; can't use the original reference
Query deleteQuery = deleteRef.orderByValue().equalTo(itemToDelete);
deleteQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
// If the value to delete is not unique, there may be multiple children
for (DataSnapshot child : dataSnapshot.getChildren()) {
// TODO Should also check the result of removeValue()
// using a CompletionListener or the returned Task
// in case you don't have write access
child.getRef().removeValue();
Log.d(TAG, "onDataChange: Removed " + child.getKey());
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Often get here because of a protection violation;
// i.e. the security rules are not set to grant read access.
// One option is to log the failure
Log.e(TAG, "onCancelled: FAILED " + databaseError.getMessage());
// Or you can also throw the exception
throw databaseError.toException();
}
});