delete/recreate realm if migration failed

[semenoh]

It's easy to delete realm when migration needed in config. But I'd like to do a migration and delete realm only if migration failed.
I've tried to wrap migration code in try/catch block but realm.deleteAll() does not do the trick.

Please provide some documentation on this.

And BTW. Do the migration is performed in transaction ? Sometimes it looks like failed migration broke the data so fixed migration does not help...

Thanks in advance

[cmelchior]

Something like this in a wrapper method should work:

        Realm realm;
        RealmConfiguration config = getConfig();
        try {
            realm = Realm.getInstance(config); // Will migrate if needed
        } catch (RealmMigrationNeededException e) {
            Realm.deleteRealm(config);
            realm = Realm.getInstance(config);
        }
        return realm;

In the future, this kind of questions are better asked on Stack Overflow where more people will be able to answer it.

[jpmcosta]

I'm trying to implement what @cmelchior mentioned:

Realm realm;
RealmConfiguration config = getConfig();
try {
    realm = Realm.getInstance(config); // Will migrate if needed
} catch (RealmMigrationNeededException e) {
    Realm.deleteRealm(config);
    realm = Realm.getInstance(config);
}
return realm;

However, I'm consistently getting the following exception when the migration fails:
java.lang.IllegalStateException: It's not allowed to delete the file associated with an open Realm. Remember to close() all the instances of the Realm before deleting its file: <file>

I've simplified my workflow to make sure it's the only instance I'm trying to open.

[RemyTabardel]

Is there a solution for that ?
I've same IllegalStateException, i just call Realm.init() before try/catch as @cmelchior and deleteRealm throw this exception.

[Zhuinden]

You can also try my slightly experimental lib called RealmAutoMigration, it works for Realm 4.x+ if you annotate your RealmList fields with @RealmAutoMigration.MigratedList.

Make sure you return; out (or apply transform() afterwards, but still ignore the later versions) of the migration once applied, because it uses your latest models.

[RemyTabardel]

I can't really use experimental lib in professional project i think.. =x
I updated my realm from 3.0.0 to 4.1.0 directly, so i tried to come back to 3.0.0 and i have not this IllegalStateException with this release.

Maybe i missed something in changelog..

[Zhuinden]

Technically it's "experimental" only because I was lazy to write automated integration tests, but otherwise it works

Either way, if nothing works, you can check the current schema version without opening a typed realm using DynamicRealm.getInstance(), and if the schema version is below a certain number, you can close the dyn realm and call deleteRealm

[RemyTabardel]

I tried to check with DynamicRealm and it's working yes.
I'll take a look about your lib, i don't want to check if i need to delete base every schema update.

Thanks @Zhuinden !

[AamirAbro]

is there any other way to fix it except for auto migration?

[AamirAbro]

the solution by @jpmcosta used to work this a new regression in 4.1.1 as far as I can tell.
can we treat as a regression issue and fix this.