Hi,
First of all I would like to mention that the version you have is just for preview and not for development. It will stop working at some point and there won't be any upgrade or transition possible to the final Kentico 8 release.
In your case, you could be using CustomTableItemProvider.GetItems(className) which is returning ObjectQuery. I think this should be what you are looking for.
Best regards,
Juraj Ondrus