Firebase Database stops syncing

Question

I have been using Firebase Database in my Android app for almost a year now and it works pretty nice. Unfortunately the data stops being synced to the could after some time. It is just never synced/stored to the cloud. Only local. So when user reinstalls the app, it only contains the data which was stored in the cloud. So to the user it looks like the data was removed, but actually is was never stored. I checked and the data is not visible in the firebase-console. Because it happens after a reinstall I guess it has something to do with the syncing. Users report losing data of about 2-3 months.

I'm using the following singleton helper class. Note I use the setPersistenceEnabled(true) and keepSynced(true).

public class FirebaseHelper{

    protected FirebaseHelper(Context c) {
        this.c = c.getApplicationContext();
        FirebaseDatabase.getInstance().setPersistenceEnabled(true);
        mAuth = FirebaseAuth.getInstance();
        this.userRef = FirebaseDatabase.getInstance().getReference().child(((BuildConfig.DEBUG ? "debug" : "release"))).child("users").child(getUID());
        this.userRef.keepSynced(true);
        this.path1 = userRef.child("path1");
        this.path2 = userRef.child("path2");
        this.path3 = userRef.child("path3");
        this.path4 = userRef.child("path4");
    }

    public static FirebaseHelper getInstance(Context c) {
        if (instance == null) {
            instance = new FirebaseHelper(c);
        }
        return instance;
    }


    public String insertObject(MyObject obj) {
        DatabaseReference newItem = this.path1.push();
        String pushID = newItem.getKey();
        obj.id = pushID;
        newItem.setValue(obj.getObject());

        return pushID;
    }

    public void updateData(...){}

    ...other methods

}

What could possibly be the cause of this?

Answer 1

There are only three reasons for this to happen to the best of my knowledge.

1) The method getUID()

Somehow the getUID() method is returning a null or invalid value which leads the data to be stored to somewhere else or it is not getting stored at all.

You are using simply getUid() instead of FirebaseAuth.getInstance().getCurrentUser().getUid(). So it must be a user defined method.

I think your getUid() does something like this.

String getUid() {
    try{
        return FirebaseAuth.getInstance().getCurrentUser().getUid() ;
    } catch (NullPointerException e) {
        return null;
    }
}

FirebaseAuth.getInstance().getCurrentUser() will return null if cache is cleared. It will lead your data to be lost.

2) Redundant data

Since Marshmallow, data is backed up to the cloud including shared preference. If you are checking shared preference to decide if user is logged in, user will be gone taken inside after reinstalling the app, skipping the login page. But actually he is not logged in which means FirebaseAuth.getInstance().getCurrentUser() returns null and any attempt to access the database will fail (depends on your database rules).

Solution: use FirebaseAuth.getInstance().getCurrentUser()==null to check if user is enabled. You can alternatively set backup to false. But I prefer first method.

3) An internal bug in Firebase SDK

Unfortunately there is nothing much we can do with it. Try narrowing it down and find a scenario by which the issue can be reproduced and report it to Firebase.

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By the way, child(((BuildConfig.DEBUG ? "debug" : "release"))) is really smart. I am going to adopt it.

Answer 2

Well, if your database has been syncing and you have not made any changes to the code whatsoever, it means that this is a firebase error, particularly related to the mobile phone the user is using.

Most developers who use firebase find problems querying the database when certain carriers are used. I have researched into this issue but i have not yet resolved it yet. If you happen to be using mobile data, actions like authenticating a user may not work.

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Solution

Use a different internet source to test your code. Try using wifi instead of mobile data while debugging or testing your app.

if I find any helpful work around, I will file it on a firebase project experiencing the problem on open source Lucem

Answer 3

Throwing this out as a guess as well: At some point you distributed an app where BuildConfig.DEBUG = true, so users that install an updated version "lose" their data. Doesn't explain why other users haven't reported shorter losses though...

The solution would be a data migration, checking which has newer data and then copying the data if DEBUG is newer.