We have an Address entity (probably actually a value object). Both a Customer and a User can have an Address. Each Address is only associated to a single Customer or User. Typically I have handled this with a unidirectional relationship. You can navigate from Customer or User to Address but not vice versa.

However for a specific business requirement I need to be able to navigate the other way. I can make this work using a one-to-one mapping to Customer and User on the Address (the many-to-one relationships on the Customer and User entities are unchanged).

However when hydrating the the Address from the database a SELECT statement is executed for each possible relationship. I can live with this but eventually Address could be associated to a lot more entities and at that point the superfluous queries would become more of a concern.

Is there an alternative mapping that would better suit my needs?

No one made any suggestions. What I was looking for was a bag like collection that holds zero or one entities. So in the Address mapping file I used a bag and in the domain object I did this: