hibernate联合主键的创建方式
总结个hibernate联合主键的创建方式，刚看完兵爷的视频，赶紧弄下来。冬爷，赶紧膜拜知道不？我这弄下来是为了明天面试，压力大很知道不？
联合主键，讲一张表中两个属性同时作为主键。
student.java

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.IdClass;

@Entity
@IdClass(value=StudentPK.class)
public class Student {

//@EmbeddedId
//private StudentPK pk;
@Id
private int id;
@Id
private String name;

//public StudentPK getPk() {
//return pk;
//}
//public void setPk(StudentPK pk) {
//this.pk = pk;
//}
private int age;

public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}

}
还有另外一个类专门设立有关主键的两个变量。
studentPK.java

package com.hibernate.finalmodel;import java.io.Serializable;import javax.persistence.Embeddable;public class StudentPK implements Serializable {private int id;private String name;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public boolean equals(Object o) {if(o instanceof StudentPK) {StudentPK pk = (StudentPK) o;if(this.id == pk.getId() && this.name.equals(pk.getName()))return true;}return false;}public int hashCode() {return this.name.hashCode();}}

这里必须重写equals和hashcode方法。重写hashcode是要定位name属性是否一致，在内存中，hashcode相同的对象线性储存。找到相同的hashcode后，在比较equals，从而得到联合主键的比较结果。
写一个单元测试
TestBase.java

package com.hibernate.finaltest;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.AnnotationConfiguration;import org.junit.After;import org.junit.AfterClass;import org.junit.Before;import org.junit.BeforeClass;import org.junit.Test;import com.hibernate.finalmodel.Student;import com.hibernate.finalmodel.StudentPK;public class TestBase {private static SessionFactory sessionFactory = null;Session session;@BeforeClasspublic static void preMethod() {sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();//if(session == null) //session = sessionFactory.openSession();//else//session = sessionFactory.getCurrentSession();}@AfterClasspublic static void postMethod() {sessionFactory.close();}@Testpublic void testMethod() {System.out.println("start create student");session = sessionFactory.openSession();//Student s = new Student();//s.setAge(23);//s.setName("samuel");StudentPK pk = new StudentPK();pk.setId(1);pk.setName("Andrew");Student s = new Student();//s.setPk(pk);s.setAge(7);session.beginTransaction();session.save(s);session.getTransaction().commit();session.close();}}[/code测试成功。就这么多了。明天面试就就扯这个了。    1 楼    德安德鲁    前天              冬爷鉴定完毕，碉堡了。
图样图森破