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:
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OneToOne - Objects are having one to one relationship. For example, a passenger can travel using a single ticket at time.
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OneToMany - Objects are having one to many relationship. For example, a father can have multiple kids.
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ManyToOne - Objects are having many to one relationship. For examples, multiple kids having a single mother.
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ManyToMany - Objects are having many to many relationship. For examples, a book can have mutiple authors and a author can write multiple books.
