hibernate联合主键的创建方式_JAVA_编程开发_程序员俱乐部

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;
	
	@BeforeClass
	public static void preMethod() {
		sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
//		if(session == null) 
//			session = sessionFactory.openSession();
//		else
//			session = sessionFactory.getCurrentSession();
	}
	
	@AfterClass
	public static void postMethod() {
		sessionFactory.close();
	}
	
	@Test
	public 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。