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！

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