Develop Reference

How to add new fields in Firestore Document from two different sources simultaneously?

When a new user registers in my app using firebase-authentication custom sign in using email and password, I need to update that data into my firestore.
But Firebase only has FirebaseAuth.createUserWithEmailAndPassword(email, password) to create a new account and hence I cannot update my user's username at the same time.
To update the E-Mail in Firestore, I use Firebase cloud functions. Here's the code:
export const onNewUserJoined = functions.auth.user().onCreate((user) => {
//const newUserDisplayName = user.displayName //CAN'T USE THIS. REASON is BELOW
const newUserUID = user.uid
const newUserEmail = user.email
const timeCreated = Date.now()
console.log(`${newUserUID} has joined.`)
return admin.firestore().collection('Agent').doc(`${newUserUID}`).set({"E-Mail": newUserEmail, "Time": timeCreated})
})
OK, great now I have updated the E-Mail and time created in Firestore successfully.
But next challenge is I need to update the user's username in the same Firestore document. I do it instantly after the createUserWithEmailAndPassword() like this:
DocumentReference dDocRef = FirebaseFirestore.getInstance().document(documentPath);
Map<String, Object> updateUsernameAndPhone = new HashMap<>();
updateUsernameAndPhone.put("username", username);
updateUsernameAndPhone.put("phoneData", phoneModel);
dDocRef.update(updateUsernameAndPhone).addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
Toast.makeText(getApplicationContext(), "Data successfully stored in Firestore", Toast.LENGTH_SHORT).show();
}
}).addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
Toast.makeText(getApplicationContext(), e.toString(), Toast.LENGTH_SHORT).show();
}
});
Now, it depends on who acts first, the cloud function or the user's device.
If the cloud functions act first, then there is no issue. The username and phoneModel both get updated into the document successfully. No issues.
But incase, the phone acts first then I get the following error:
As this error has occurred, username isn't in the document and only email and timeCreated are in the document updated by the cloud function which got late to create document so that user's device can update the username with ease.
I CAN'T use .SET instead of .update() in my app because if I use .set() and the cloud functions create the email and timeCreated fields first. Then the device will DELETE them and put username and phoneModel.
So how can I do this?
I can forcefully delay updating the username by putting it in the next activity so that cloud functions get enough time to do their job, but my signUpActivity asks for username along with email and password edit texts. I don't want to create a separate activity for that.
I used to use .update() when my data was stored in realtime database and it used to create the child even if the path didn't exist. But it looks firestore won't update if the field doesn't exist.
Any solution for this?
I tried as per #DougStevenson said and here's my code:
final String newUserUID = Objects.requireNonNull(signUpAuth.getCurrentUser()).getUid();
final String documentPath = "Agent/" + newUserUID;
FirebaseFirestore fFirestoreRef = FirebaseFirestore.getInstance();
final DocumentReference dDocRef = fFirestoreRef.document(documentPath);
fFirestoreRef.runTransaction(new Transaction.Function<Void>() {
#Nullable
#Override
public Void apply(#NonNull Transaction transaction) throws
FirebaseFirestoreException {
DocumentSnapshot documentSnapshot = transaction.get(dDocRef);
transaction.update(dDocRef, "username", username);
transaction.update(dDocRef, "phoneData", phoneModel);
return null;
}
}).addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
Toast.makeText(getApplicationContext(), "Data updated in Firestore . . .", Toast.LENGTH_SHORT).show();
}
}).addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
Toast.makeText(getApplicationContext(), e.toString(), Toast.LENGTH_SHORT).show();
}
});
But no luck. It still gives me error: Cannot update a document which does not exist.

Use a transaction to resolve conflicts from multiple clients that are all trying to modify the same document. The transaction handler will be retried on the client if it detects the document was modified before the change could take place.

Disable offline time insert to firebase in android?

There is an issue in my app that connect to firebase real time database ..
when i try to insert data to firebase during offline...
when internet available the data automaticaly send to firebase database..
when my app close on offline then the insert will not happen...
i want to prevent the data insert to firebase which the after effect of insert try during offline...
//------------------------------------------------
private void onStarClicked(final DatabaseReference postRef) {
postRef.runTransaction(new Transaction.Handler() {
#Override
public Transaction.Result doTransaction(MutableData mutableData) {
if (mutableData.hasChildren()) {
int inv = 0;
for (MutableData postData : mutableData.getChildren()) {
inv = postData.child("inv").getValue(Integer.class);
}
SalesModel salesModel = new SalesModel("samsung",inv+1,987.90);
String newKey = postRef.push().getKey();
// Set value and report transaction success
mutableData.child(newKey).setValue(salesModel);
}
// Set value and report transaction success
// mutableData.setValue(p);
return Transaction.success(mutableData);
}
#Override
public void onComplete(DatabaseError databaseError, boolean b,
DataSnapshot dataSnapshot) {
// Transaction completed
// Log.d(TAG, "postTransaction:onComplete:" + databaseError);
}
});
}
//------------------------------------------------------/

The Realtime Database SDK cannot be configured to ignore pending writes when the app process is killed. The SDK will always try to synchronize all writes. If you don't want this behavior, you'll have to find another way to buffer writes in memory and try to only send them when online. But I suspect you will have a lot of trouble with this, as you never have a guarantee that any write will succeed at the moment you try it.

Real-time database onDisconnect not executing after logging out

I have implemented the Firebase Real-Time Database presence system as shown in the official Firebase documentation. I would like to make the database secure so that logged-in users can only write to their own presence entries in the DB. So, on login, the user writes to the reference path /auth/{authId}/connections and at the same time sets up the onDisconnect to remove the value.
Here is the code from the Android app that is setting presence in rtdb:
getFirebaseDatabase().goOnline();
DatabaseReference.goOnline();
// Since I can connect from multiple devices, we store each connection instance separately
// any time that connectionsRef's value is null (i.e. has no children) I am offline
final FirebaseDatabase database = getFirebaseDatabase();
final DatabaseReference myConnectionsRef = database.getReference("/auth/" + getFirebaseAuth().getUid() + "/connections");
// Stores the timestamp of my last disconnect (the last time I was seen online)
final DatabaseReference lastOnlineRef = database.getReference("/auth/" + getFirebaseAuth().getUid() + "/lastOnline");
connectedRef = database.getReference(".info/connected");
presenceChangeListener = connectedRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
boolean connected = snapshot.getValue(Boolean.class);
if (connected) {
DatabaseReference con = myConnectionsRef.push();
// When this device disconnects, remove it
con.onDisconnect().removeValue()
.addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
// Add this device to my connections list
// this value could contain info about the device or a timestamp too
con.setValue("ANDROID");
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
Log.d(TAG, "### Failed to set onDisconnect ###");
e.printStackTrace();
}
});
// When I disconnect, update the last time I was seen online
lastOnlineRef.onDisconnect().setValue(ServerValue.TIMESTAMP);
}
}
#Override
public void onCancelled(DatabaseError error) {
Log.w(TAG, "Listener was cancelled at .info/connected");
}
});
The problem that I am having is that if the user logs out, the onDisconnect doesn't execute unless I first manually disconnect from rtdb. I'm assuming that the code running on the Real-Time DB gets a permission denied since the auth is no longer valid.
//If I don't go offline first the record in rtdb will not be removed.
DatabaseReference.goOffline();
AuthUI.getInstance().signOut(this)
.addOnCompleteListener(new OnCompleteListener<Void>() {
public void onComplete(#NonNull Task<Void> task) {
// user is now signed out
Log.d(TAG, "Logged out");
application.clearData();
DatabaseReference.goOffline(); //This doesn't cause a presence update here
finish();
}
});
Above is the work-around I'm using, first telling the database to goOffline then to logout. If the user ever gets logged out by another means (the web app is seeing if multiple tabs are using the app and one logs out) the user will be left with a connection not removed.
If I don't call the goOffline() prior to logout, the connection in rtdb will not be removed, even if I force close the application.
I have also verified that I can get everything working fine if I change my rtdb rules to be ".write": "true" <-which is no good. This tells me that there is a permission denied with the onDisconnect running when a user logs out of the auth.
I would like my real-time rules to be something like this.
{
"rules": {
"auth": {
"$uid": {
".read": "auth != null && auth.uid == $uid",
".write": "auth != null && auth.uid == $uid"
}
}
}
}
I would have hoped that the onDisconnect would still be able to execute with the auth of the user when the onDisconnect was setup.

When you attach a onDisconnect() handler, you're registering a delayed write on the Firebase servers. Whether that write is allowed is checked both when you attach the handler, and when the handler is triggered. And since your user is signed out when the write is triggered, it get rejected by your rules. There is no configuration option to change this behavior, so you'll have to come up with a different approach.

So, because 1.) the onDisconnect() execution is evaluated against the rules of the RTDB, 2.) the user who setup the onDisconnect() may lose authentication, and 3.) I would like to make the presence system secure for my auth'ed users... I came up with the following solution:
First, write the presence entries to the RTDB under a path that contains both the user's authId and a UUID to make the location "unguessable".
"/presence/" + {auth-uid} + "/connections/" + {UUID}
and setup a .onDisconnect() to remove this value stored at the unguessable location.
Then, setup the RTDB rules to do the following:
do not allow any reading of the presence data
allow users to add/modify data only under their auth directory
allow any user to delete records (they would need to know the unguessable path)
"presence": {
".read": "false",
".write": "false",
"$auth_id": {
"connections": {
"$uuid": {
".write": "(newData.exists() && $auth_id === auth.uid) || !newData.exists()"
}
}
}
}
Finally, setup a trigger function on the RTDB to read the .ref('/presence/{authid}') location and push the user's presence to another user accessible location (I'm pushing it to my Firestore DB). Also, if the user is changing from "online" to "offline" update a lastOnline timestamp to the current time.
This seems like the best solution given my requirements of having reliable and secure presence system. I hope this helps others.

It is an old question but it made me think about a possible solution and came with the following...
use onDisconnect.setValue/removeValue as long as you have control/awareness over the application
use onDisconnect.cancel and delete to data before logging out
I took #FrankvanPuffelen code and modified it but didn't tested it so....
//getFirebaseDatabase().goOnline();
//DatabaseReference.goOnline();
// Since I can connect from multiple devices, we store each connection instance separately
// any time that connectionsRef's value is null (i.e. has no children) I am offline
final FirebaseDatabase database = getFirebaseDatabase();
final DatabaseReference myConnectionsRef = database.getReference("/auth/" + getFirebaseAuth().getUid() + "/connections");
// Stores the timestamp of my last disconnect (the last time I was seen online)
final DatabaseReference lastOnlineRef = database.getReference("/auth/" + getFirebaseAuth().getUid() + "/lastOnline");
connectedRef = database.getReference(".info/connected");
presenceChangeListener = connectedRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
boolean connected = snapshot.getValue(Boolean.class);
if (connected) {
// simple solution to reuse the old unique key-name otherwise current solution is like performing new registration of a new client over and over on the same client. we should use the old unique key-name until logout is performed
String keyName = SharedPrefUtil.INSTANCE.getFirebaseConnectionKeyName(context);
DatabaseReference con;
if (TextUtils.isEmpty(keyName)) {
con = myConnectionsRef.push();
SharedPrefUtil.INSTANCE.setFirebaseConnectionKeyName(context.getApplicationContext(), con.getKey());
}else{
con = myConnectionsRef.child(keyName);
}
// When this device disconnects, remove it
con.onDisconnect().removeValue()
.addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
// Add this device to my connections list
// this value could contain info about the device or a timestamp too
con.setValue("ANDROID");
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
Log.d(TAG, "### Failed to set onDisconnect ###");
e.printStackTrace();
}
});
// When I disconnect, update the last time I was seen online
lastOnlineRef.onDisconnect().setValue(ServerValue.TIMESTAMP);
}
}
#Override
public void onCancelled(DatabaseError error) {
Log.w(TAG, "Listener was cancelled at .info/connected");
}
});
in the logout method we need to cancel the disconnect
String keyName = SharedPrefUtil.INSTANCE.getFirebaseConnectionKeyName(context);
if (!TextUtils.isEmpty(keyName)) {
final FirebaseDatabase database = getFirebaseDatabase();
final DatabaseReference myConnectionsRef = database.getReference("/auth/" + getFirebaseAuth().getUid() + "/connections/" + keyName);
// Stores the timestamp of my last disconnect (the last time I was seen online)
final DatabaseReference lastOnlineRef = database.getReference("/auth/" + getFirebaseAuth().getUid() + "/lastOnline");
// This client/user doesn't need the disconnect functionality
myConnectionsRef.onDisconnect().cancel();
// now we are on our own so we need to remove the key-name from the rmdb
myConnectionsRef.setValue(null);
// remove the key-name from the preferences so we will create a new one in the next login session
SharedPrefUtil.INSTANCE.removeFirebaseConnectionKeyName(context);
// we will not forget to disconnect last time updates
lastOnlineRef.onDisconnect().cancel()
}
AuthUI.getInstance().signOut(this)
I didn't tested it and it will not run as it is missing the SharedPrefUtil implementation

How to know which user is trying to Sign-in?

Users are created using Email and Password. This is how I do the Sign-up:
mSignup.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mEmailStr = removeSpaces(mEmail.getText().toString());
mPasswordStr = mPassword.getText().toString();
mUsernameStr = mUsername.getText().toString();
mIsSgl = mSglCheckBox.isChecked();
mUsernameStr=mUsername.getText().toString();
final User mUser = new User();
mUser.setEmail(mEmailStr);
mUser.setPassword(mPasswordStr);
mUser.setIsSgl(mIsSgl);
mUser.setStudyGroupName(mStudyGroupName);
mUser.setUsername(mUsernameStr);
FirebaseAuth.getInstance().createUserWithEmailAndPassword(mUser.getEmail(), mUser.getPassword()).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(Task<AuthResult> task) {
if (task.isSuccessful()) {
Toast.makeText(getActivity(), "Sucsses", Toast.LENGTH_SHORT).show();
generateUser(mUser);
startActivity(new Intent(getActivity(), MainActivity.class));
} else {
Toast.makeText(getActivity(), "not Sucsses", Toast.LENGTH_SHORT).show();
}
}
});
}
});
This is how I push the data into database:
public void generateUser(User user)
{
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference users;
if(user.getIsSgl())
{
users = database.getReference(user.getStudyGroupName()).child("SGL");
}
else
{
users = database.getReference(user.getStudyGroupName()).child("Student");
}
users.push().setValue(user);
}
This is how I Sign-in:
mSignin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mEmailStr = SignupActivityFragment.removeSpaces(mEmail.getText().toString());
mPasswordStr = mPassword.getText().toString();
mAuth.signInWithEmailAndPassword(mEmailStr, mPasswordStr).addOnCompleteListener(getActivity(), new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(Task<AuthResult> task) {
if (task.isSuccessful()){
FirebaseDatabase database = FirebaseDatabase.getInstance();
// thats not worked for me
database.getReference("StudyGroups").child("Student").orderByChild("email").equalTo(mEmailStr).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childSnapShot : dataSnapshot.getChildren()) {
userKey = childSnapShot.getKey();
}
Toast.makeText(getContext(),"Userkey: " + userKey,Toast.LENGTH_LONG).show();
Log.v("himaAbousalem",userKey);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Toast.makeText(getActivity(), "Sucsses ", Toast.LENGTH_SHORT).show();
startActivity (new Intent(getActivity(),Controller.class));
}else {
Toast.makeText(getActivity(), "not sucsses", Toast.LENGTH_SHORT).show();
}
}
});
}
});
I want to query the database so that when a user signs-in by Email and password, it returns all the data of that user from the database.
How can I make the key of userId in Auth equal to the userId in database and how do I use that feature?

tl;dr - In this case, store each user using their associated uid generated by Fireabase Auth instead of using a push ID.
In your situation the challenge with using a push ID to store info specific to each user is that when a user signs in you don't know the push ID you used when you first stored their info. To find a user each time they sign in you would have to search through every user in your database until you find a matching email/password to retrieve their correct profile information - the more users you have, the longer it would take to do the search. One alternative, which would probably be faster, is to use Firebase Authentication to create users and the Firebase Database to store any user specific information.
When you create a new user using Firebase Authentication it will assign a unique user id to the user that will be the same throughout the lifetime of the user. You then use the unique user id generated by Firebase Auth instead of a push ID to store user info in the database. The next time a user signs in you get the user's uid from Firebase Auth and use it to query the database to get that user's information.
Check the guide for how to create a password-based user and how to sign a user in using Firebase Auth: Create a password-based account
In order to use the unique uid generated by Firebase Auth I suggest a few changes to your code.
Update database structure
I suggest you update your database structure by adding a new location (maybe "allUsers") for use when you create/sign in users. Right now it looks like your are breaking up students into groups. If you need to keep this structure, for reasons beyond authentication, you can use it along with my suggestion. The reason for a single location which stores all users is that you need a definite location to query when a user signs in. When using Firebase Auth, without a single location which stores all users there is no way to tell what group a user belongs to when they first sign in. You would have to check every group in order to find a match and that may take a long time. Having a location which stores all users solves that problem. Also, the query for retrieving user information from that single location is much simpler. If you do need to keep a user's information in multiple places just be sure to update their information in both places if any changes occur.
Create a class variable used to distinguish between create user and sign in existing user.
If you use the same Activity to create a new user and sign in an existing user then create a boolean variable to make a distinction between when a new user is being created and when an existing user is signing in. It will be used later in the AuthStateListener. If you handle user creation in a separate activity from general sign in then you shouldn't need this variable because each activity would have a separate AuthStateListener.
boolean mIsNewUser = false;
Move the call to generateUser() from the create user completion listener to an AuthStateListener. Also move your database query from the sign in completion listener to the AuthStateLisener
Whenever you create a user successfully they will automatically be signed in too. So, if you move your call to generateUser() from the createUserWithEmailAndPassword OnCompleteListener to your AuthStateListener you can get access to the created user's uid. When signing an existing user move your database query to the AuthStateListener as well, again so we can access the user's uid. I'm also going to create a helper method for the database query called getExistingUserInfo. As an FYI, the onComplete() callback in the OnCompleteListeners for creating and signing in users gives you access to an AuthResult which according to the API has a method for returning the current user but the documentation says to access user information in the AuthStateListener.
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
#Override
protected void onCreate(Bundle savedInstanceState) {
mAuth = FirebaseAuth.getInstance();
mAuthListener = new FirebaseAuth.AuthStateListener() {
#Override
public void onAuthStateChanged(#NonNull FirebaseAuth firebaseAuth) {
FirebaseUser user = firebaseAuth.getCurrentUser();
if (user != null) {
// User is signed in
Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());
if(mIsNewUser){
//call to generate user using Uid instead of pushID
generateUser(mUser, user.getUid());
} else{
getExistingUserInfo(user.getUid());
}
startActivity(new Intent(getActivity(), MainActivity.class));
} else {
// User is signed out
Log.d(TAG, "onAuthStateChanged:signed_out");
}
// ...
}
};
// ...
}
}
#Override
public void onStart() {
super.onStart();
mAuth.addAuthStateListener(mAuthListener);
}
#Override
public void onStop() {
super.onStop();
if (mAuthListener != null) {
mAuth.removeAuthStateListener(mAuthListener);
}
}
Update your generateUser() helper method to use the uid instead of a push ID:
I'm going to assume you want to keep you existing database structure and add the single location for all users as suggested. Based on this I've made a couple of changes to the write operation you were using in generateUser(). Mainly, instead of using setValue() to write to the database I'm using updateChildren(). By using updateChildren() we can take advantage of Firebase's ability to do atomic updates. This will allow us to write to the appropriate student group location and the location storing all users simultaneously. By taking this approach if the write operation to either location fails neither location will be updated. This way you can be certain if a student is added to a group they will also be listed in the allUsers location.
private void generateUser(User user, String uid)
{
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
String userType;
String allusers = "allUsers/" + uid;
Map<String, Object> newUserUpdate = new HashMap<>();
if (user.getUsername() != null) {
if (user.isSgl()) {
userType = user.getStudyGroupName() + "/" + "SGL" + "/" + uid;
} else {
userType = user.getStudyGroupName() + "/" + "Student" + "/" + uid;
}
newUserUpdate.put(userType, user.serialize());
newUserUpdate.put(allusers, user.serialize());
database.updateChildren(newUserUpdate);
}
}
Update database query to use new location which stores all users
As I mentioned above, by creating a single location for all users you can reduce the complexity of the query used to find a user's info when they sign in. Again, if you need to store users by group you can keep that but be sure to update both locations if a users info changes.
public void getExistingUserInfo(String uid){
FirebaseDatabase database = FirebaseDatabase.getInstance();
database.getReference("allUsers").child(uid).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//get user data from dataSnapshot
Toast.makeText(getContext(),"Userkey: " + userKey,Toast.LENGTH_LONG).show();
Log.v("himaAbousalem",userKey);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
Set the variable used to distinguish between existing user sign in and new user creation in the create user completion listener
FirebaseAuth.getInstance().createUserWithEmailAndPassword(mUser.getEmail(), mUser.getPassword()).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(Task<AuthResult> task) {
if (task.isSuccessful()) {
//set boolean used in the AuthListener
mIsNewUser = true;
Toast.makeText(getActivity(), "Sucsses", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getActivity(), "not Sucsses", Toast.LENGTH_SHORT).show();
}
}
});

Data not getting saved in Firebase database from android

I am using the new Firebase console. I am trying to save an object to the database but its not getting saved. Following is the code.
DatabaseReference mFirebaseRef = FirebaseDatabase.getInstance().getReference();
mFirebaseRef.push().setValue(object, new DatabaseReference.CompletionListener() {
#Override
public void onComplete(DatabaseError databaseError, DatabaseReference reference) {
if (databaseError != null) {
Log.e(TAG, "Failed to write message", databaseError.toException());
}
}
});
the 'object' is created properly. There is no error I am getting and I have checked in debugging that the onComplete method is not getting triggered.
Security Rule is also true for write.

Note that DatabaseReference.CompletionListener fires "when an operation has been acknowledged by the Database servers". Is it possible you did not have a network connection at the time you ran your test? I copied your code and ran it successfully on a phone with object defined like this:
Object object = new String("Test");
I then enabled airplane mode, re-ran the code and observed the behavior you describe. The completion listener did not fire until I disabled airplane mode and a network connection was established.
Example code for checking the status of your network connection is provided in this documentation.

use the below code:
mFirebaseRef.push().setValue(object).addOnCompleteListener(new OnCompleteListener<Void>()
{
#Override
public void onComplete(#NonNull Task<Void> task) {
if(task.isSuccessful()){
// write code for successfull operation
}
}
});
}
.push will generate a random key on which your data will stored if you do not use .push it will overwrite on previous stored data.