Java Persistence with Hibernate

7.2. Many-valued entity associations

A many-valued entity association is by definition a collection of entity references. You mapped one of these in the previous chapter, section 6.4, "Mapping a parent/children relationship." A parent entity instance has a collection of references to many child objects—hence, one-to-many.

One-to-many associations are the most important kind of entity association that involves a collection. We go so far as to discourage the use of more exotic association styles when a simple bidirectional many-to-one/one-to-many will do the job. A many-to-many association may always be represented as two many-to-one associations to an intervening class. This model is usually more easily extensible, so we tend not to use many-to-many ...