JPA一对一映射案例
双向和单向的区别,其实不在数据库,而在加载方向。如Student和StudentNo,单向是Student拥有StudentNo的实例可以加载StudentNo,而双向不但Student可以加载StudentNo,StudentNo可以拥有Student实例来加载Student。数据库里是两个共享主键的表
以下模拟双向一对一得映射案例:
表结构如下:
Student表结构:
StudentNo表结构:
首先需要加入JPA的jar包,别忘了数据库驱动,如图
建数据库连接配置文件META-INF/persistence.xml
<?xml version="1.0"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
<persistence-unit name="jason" transaction-type="RESOURCE_LOCAL">
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.OracleDialect"/>
<property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver"/>
<property name="hibernate.connection.url" value="jdbc:oracle:thin:@localhost:1521:ORCL"/>
<property name="hibernate.connection.username" value="jason"/>
<property name="hibernate.connection.password" value="jason"/>
<property name="hibernate.max_fetch_depth" value="3"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
<property name="hibernate.show_sql" value="false"/>
<property name="hibernate.format_sql" value="false"/>
</properties>
</persistence-unit>
</persistence>
Student类:
package com.jason.bean;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
/**
* 学员
*
* @author jason
*
*/
@Entity
public class Student {
private Integer id;
private String name;
private StudentNo studentNo;
public Student() {
super();
}
public Student(String name) {
super();
this.name = name;
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Column(nullable = false, length = 20)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
//optional = true指明StudentNo可为空
//mappedBy="student"指明Student作为双向关系的维护段,负责外键的更新,起主导作用
@OneToOne(optional = true, cascade = CascadeType.ALL, mappedBy="student")
public StudentNo getStudentNo() {
return studentNo;
}
public void setStudentNo(StudentNo studentNo) {
this.studentNo = studentNo;
}
}
StudentNo类:
package com.jason.bean;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
/**
* 学员编号
*
* @author jason
*
*/
@Entity
public class StudentNo {
private Integer id;
private String stuno;
private Student student;
public StudentNo() {
super();
}
public StudentNo(String stuno) {
super();
this.stuno = stuno;
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Column(length = 18,nullable = false)
public String getStuno() {
return stuno;
}
public void setStuno(String stuno) {
this.stuno = stuno;
}
//unique= true 指明studentid列的值不可重复
//optional = false指明Student不可为空
@OneToOne(cascade = CascadeType.ALL, optional = false)
@JoinColumn(name = "studentid",referencedColumnName="id", unique = false)
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
}
OneToOneTest测试类:
package junit.test;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
import com.jason.bean.Student;
import com.jason.bean.StudentNo;
public class OneToOneTest {
private static EntityManagerFactory factory;
private static EntityManager em;
@BeforeClass
public static void setUpBeforeClass() throws Exception {
factory = Persistence.createEntityManagerFactory("jason");
em = factory.createEntityManager();
em.getTransaction().begin();
}
/**
* 添加学员时同时添加对应的学员编号
*/
@Test
public void save() {
Student student = new Student();
student.setName("jason");
StudentNo sn=new StudentNo();
sn.setStuno("110");
sn.setStudent(student);
student.setStudentNo(sn);
em.persist(student);
}
/**
* 删除
*/
@Test
public void delete() {
//删除学员同时会自动删除学员编号
em.remove(em.getReference(Student.class, 13));
//删除学员编号同时删除学员
// em.remove(em.getReference(StudentNo.class, (Serializable)6));
}
/**
* 更新
*/
@SuppressWarnings("unchecked")
@Test
public void update() {
List<Student> students=em.createQuery("select o from Student o").getResultList();
for(Student sutdent : students){
sutdent.setName("张三");
StudentNo sn=sutdent.getStudentNo();
if(sn!=null){
sn.setStuno("123");
}
em.merge(sutdent);
}
}
/**
* 用来判断映射是否成功
*
*/
@Test
public void test() {
Persistence.createEntityManagerFactory("jason");
}
@AfterClass
public static void tearDownAfterClass() throws Exception {
em.getTransaction().commit();
em.close();
factory.close();
}
}
JUnit运行测试!