Jan-Willem, thanks very much for your feedback!
You may be right about Hibernate not allowing a formula for a composite ID
property. It appears it's not allowed when hbm mapping is used. I'll have
to check to see if a formula is allowed when mapped with annotations..
Looking a the mapping for Add
PostgreSQL doesn’t allow nullable columns in a compound primary key. It allows
a unique constraint on a nullable column, but then it happily inserts the two
values below - without constraint violation error.
I too have stumbled upon the need for nullable identifiers in Hibernate
however. Mostly
