Hibernate @IdClass @EmbeddedID相关注解

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Hibernate Annotations

Mapping composite primary keys and foreign keys to composite primary keys：

http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html_single/#d0e2177

引用Composite primary keys use a embedded class as the primary key representation, so you'd use the @Id and @Embeddable annotations. Alternatively, you can use the @EmbeddedId annotation. Note that the dependent class has to be serializable and implements equals()/hashCode(). You can also use @IdClass.

@Entitypublic class RegionalArticle implements Serializable {    @Id    public RegionalArticlePk getPk() { ... }}@Embeddablepublic class RegionalArticlePk implements Serializable { ... }

or alternatively

@Entitypublic class RegionalArticle implements Serializable {    @EmbeddedId    public RegionalArticlePk getPk() { ... }}public class RegionalArticlePk implements Serializable { ... }

hibernate的annotation的文档中提供了三种方法
　　1 将组件类注解为@Embeddable,并将组件的属性注解为@Id
　　2 将组件的属性注解为@EmbeddedId (方便)
　　3 将类注解为@IdClass,并将该实体中所有属于主键的属性都注解为@Id(符合编程习惯)
主键类需要序列化(考虑到可能会将数据读写到虚拟内存中),需要重写hashcode()和equals()方法,因为要对联合主键进行比较.

Hibernate Annotation 联合主键三种写法的例子：
http://laodaobazi.iteye.com/blog/903236
Which anotation should I use: @IdClass or @EmbeddedId:
http://stackoverflow.com/questions/212350/which-anotation-should-i-use-idclass-or-embeddedid

Compound Primary Keys with Hibernate and JPA Annotations:
http://jpa.ezhibernate.com/Javacode/learn.jsp?tutorial=15usingcompoundprimarykeys

@IdClass and @EmbeddedId:
http://www.coderanch.com/t/452567/ORM/java/IdClass-EmbeddedId

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