====== JPA Composite Primary Key ======
  * JPA 복합키
  * [[http://stackoverflow.com/questions/212350/which-annotation-should-i-use-idclass-or-embeddedid|java - Which annotation should I use: @IdClass or @EmbeddedId]] - 둘 중에 ''@IdClass''가 더 사용하기 편하다는 얘기

===== @IdClass =====

===== @EmbeddedId =====

===== @AttributeOverrides =====

===== 다른 엔티티들을 복합키로 가지기 =====
  * [[http://www.java2s.com/Code/Java/JPA/SetIdClassforCompoundKey.htm|Set IdClass for Compound Key : Primary Key]]

<code java>
@Entity
@Table(name = "EMP_PROJECT")
@IdClass(ProjectAssignmentId.class)
public class ProjectAssignment {
  @Id
  @Column(name = "EMP_ID", insertable = false, updatable = false)
  private int empId;

  @Id
  @Column(name = "PROJECT_ID", insertable = false, updatable = false)
  private int projectId;

  @ManyToOne
  @JoinColumn(name = "EMP_ID")
  Professor employee;

  @ManyToOne
  @JoinColumn(name = "PROJECT_ID")
  Project project;
  ..
}

public class ProjectAssignmentId implements Serializable {
  private int empId;
  private int projectId;
  ...
}
</code>

===== 참조 =====
  * [[https://www.javacodegeeks.com/2019/04/identifiers-hibernate.html|Identifiers In Hibernate | Java Code Geeks - 2019]]