Hibernate mapping a composite key with null values

Question

With Hibernate, can you create a composite ID where one of the columns you are mapping to the ID can have null values?

This is to deal with a legacy table that has a

Answer 1

For composite keys (assumed that database allows nulls in PKs) you can have maximum number_of_cols^2 - 1 entries containing nulls, (for example for composite key of 2 columns you can have 3 rows having in their primary key null, the fourth is the PK without nulls).