Example code in the scrolling document might not consume every element in the database.

[r6hk]

The example code in the document:

Window<User> users = repository.findFirst10ByLastnameOrderByFirstname("Doe", ScrollPosition.offset()); do { for (User u : users) { // consume the user } // obtain the next Scroll users = repository.findFirst10ByLastnameOrderByFirstname("Doe", users.positionAt(users.size() - 1)); } while (!users.isEmpty() && users.hasNext());

The execution result is as follows (there are slight differences from the code in the documentation, but it illustrates the point):

It can be observed that the elements with indices 10 through 14 have not been consumed.

Modified code:

ScrollPosition position = ScrollPosition.offset(); while (true) { users = repository.findFirst10ByLastnameOrderByFirstname("Doe", position); if (users.isEmpty()) break; for (User u : users) { // consume the user } if (!users.hasNext()) break; position = users.positionAt(users.size() - 1); }

This code accounts for more cases, such as when the count of data is 0 or an exact multiple of 10.

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[mp911de]

Thanks for bringing this up. Actually, the condition is slightly off, it should be || instead of &&, so either the result has contents or the scrolling isn't finished yet. Do you want to include the change or should we just swap the operators?

[r6hk]

Thanks for bringing this up. Actually, the condition is slightly off, it should be || instead of &&, so either the result has contents or the scrolling isn't finished yet. Do you want to include the change or should we just swap the operators?

Thank you for the feedback. It looks like simply changing the operator is the easier fix—please go ahead and change it directly. However, also note that when no results are found for the given query, users.positionAt(users.size() - 1) could throw an IndexOutOfBoundsException.

[r6hk]

You can still consider my code, as I believe it reduces one interaction with the database. @mp911de

[mp911de]

Thank you for your contribution. I refined the code example and now it doesn't skip the last batch. The example complexity suggests also now using WindowIterator as optimizations quickly end up in a bit of complexity what should actually be a rather simple iteration loop.