EJB 3.0 provides option to define database entity relationships/mappings like one to one, one to many, many to one and many to many relationships. Following are the relevant annotations:
-
OneToOne - Objects are having one to one relationship. For example, a passenger can travel using a single ticket at time.
-
OneToMany - Objects are having one to many relationship. For example, a father can have multiple kids.
-
ManyToOne - Objects are having many to one relationship. For examples, multiple kids having a single mother.
-
ManyToMany - Objects are having many to many relationship. For examples, a book can have mutiple authors and a author can write multiple books.