@Bobino Oh, dear - I really wasn't thinking far enough. I was so busy trying to understand the concept of nested sets that I didn't think about transactions at all. Of course, that makes my question superfluous, since no record is blocked long enough.After all, if I catch an error, I can just try the commit again a second later until it works.
I use transactions almost everywhere. Not only for data integrity, but also for a better user experience. I've often observed that users struggle with remembering to click outside of a field to save the input. That's why I generally prevent accidental comitting. The action is always completed by clicking a done or save button. That way the users understand what’s happening.
So - thank you for opening my eyes!
I am very interested in this nested set model because I want to use a tree structure in an app. Unfortunately, I haven't found a tree structure yet that was fast enough when opening or closing nodes when dealing with more than - let's say - a few hundred records.