How To Define A Composite Primary Key Via @IdClass

Description: This application is a proof of concept of how to define a composite key via @IdClass. This application uses two entities, Author and Book involved in a lazy bidirectional @OneToMany association. The identifier of Author is composed by name and age via AuthorId class. The identifier of Book is just a typical auto-generated numeric value.

Key points:

• the composite key class (e.g., AuthorId) is public
• the composite key class must implement Serializable
• the composite key must define equals() and hashCode()
• the composite key must define a no-arguments constructor

Note: The @IdClass can be useful when we cannot modify the compsite key class. Otherwise, rely on @Embeddable.

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