一个数据库表中其主键有可能不止一个属性,同样映射到实体类中,可能有两个或多个属性共同配置成为一个主键,假设一个实体类Score,其主键有两个属性stuId(学生编号)和subjectId(科目编号),在hibernate环境下应该这样配置:
新建一个实体类ScoreId,属性为stuId,和subjectId,该类需要实现serializable接口(最好重写equals方法和hashcode方法):
public class ScoreId implements Serializable {
private int stuId;
private int subjectId;
public int getStuId() {
return stuId;
}
public void setStuId(int stuId) {
this.stuId = stuId;
}
public int getSubjectId() {
return subjectId;
}
public void setSubjectId(int subjectId) {
this.subjectId = subjectId;
}
public ScoreId(int stuId, int subjectId) {
super();
this.stuId = stuId;
this.subjectId = subjectId;
}
}
新建实体类Score:
public class Score {
private ScoreId scoreId;
private double result;
public ScoreId getScoreId() {
return scoreId;
}
public void setScoreId(ScoreId scoreId) {
this.scoreId = scoreId;
}
public double getResult() {
return result;
}
public void setResult(double result) {
this.result = result;
}
public Score(ScoreId scoreId, double result) {
super();
this.scoreId = scoreId;
this.result = result;
}
}
其次是Score.hbm.xml配置文件:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.wang.pojo">
<class name="Score" >
<composite-id name="scoreId" class="ScoreId">
<key-property name="stuId"></key-property>
<key-property name="subjectId"></key-property>
</composite-id> <property name="result"></property>
</class>
</hibernate-mapping>
hibernate.cfg.xml这里就省略了,现在新建一个测试类,用于生成数据库表以及向数据库中存放一条数据:
@Test
public void testCreateDB(){
Configuration cfg = new Configuration().configure();
SchemaExport se=new SchemaExport(cfg);
//第一个参数是否生成ddl脚本 第二个参数是否执行到数据库
se.create(true,true);
}
@Test
public void testSave(){
Session session = HibernateUtil.getSession();
Transaction tx = session.beginTransaction();
Score s=new Score(new ScoreId(2,5),88);
session.save(s);
tx.commit();
session.close();
}