How to handle Realm transactions on Android

In several pieces of sample code out there, I've seen patterns that look like this:

try (Realm realm = Realm.getDefaultInstance()) {
  realm.beginTransaction();
  workWithRealmData();
  realm.commitTransaction();
}

The question is - is this safe? If the "workWithRealmData()" function throws an exception, the transaction won't be canceled. But we are closing the Realm anyway in the finally of the try-with-resources.

A safer construction might look like the following:

try (Realm realm = Realm.getDefaultInstance()) {
  realm.beginTransaction();
  try {
    workWithRealmData();
    realm.commitTransaction();
  } finally {
    if (realm.isInTransaction()) {
      realm.cancelTransaction();
    }
  }
}

That looks safer - but also looks significantly nastier to code for all callsites.

So really this boils down to - is it safe to ignore cancelTransaction if the Realm is closed immediately afterwards, or not? If not, what could go wrong?

You can use executeTransaction(Realm.Transaction) method which automatically cancels the synchronous transaction in case of error.

try(Realm r = Realm.getDefaultInstance()) {
    r.executeTransaction((realm) -> {
        workWithRealmData();
    });
}