Jumping in late on this one but I wanted to point out that even if you could read it prior to committing to check if your constraint is maintained, most of the JG storage layers do not provide ACID guarantees. FoundationDB is the one distributed option, and BerkeleyDB can do it for a single instance setup. Since you do not have ACID guarantees in most cases, I think you could still have a case where another transaction commits prior to your commit even though you saw isPublished = false when you check it. One possible way around this without ACID would be to process all mutations for a branch on one thread, effectively single threading access to it so that you could know that no other user was writing to the branch while you were reading.

--Ted