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Person和IdCard，单向是Person拥有IdCard的实例可以加载IdCard，而双向不但Person可以加载IdCard，IdCard可以拥有Person实例来加载Person。数据库还是原来的数据库(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：

Person表结构

IdCard表结构

 

IDCard类

package com.ljq.entity;

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;
import javax.persistence.Table;
/**
 * 身份证
 * 
 * @author jiqinlin
 *
 */
@Entity
@Table(name = "tb_idcard")
public class IDCard {
    @Id
    @GeneratedValue
    private Integer id;
    
    @Column(nullable = false, length = 18)
    private String cardno;
    
    //unique= true 指明personid列的值不可重复。
    //optional = false指明Person不可为空
    @OneToOne(cascade = CascadeType.ALL, optional = false)
    @JoinColumn(name = "personid",referencedColumnName="id", unique = true)
    private Person person;

    public IDCard() {
        super();
    }
    
    public IDCard(String cardno) {
        super();
        this.cardno = cardno;
    }


    public String getCardno() {
        return cardno;
    }

    public void setCardno(String cardno) {
        this.cardno = cardno;
    }


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }


    public Person getPerson() {
        return person;
    }

    public void setPerson(Person person) {
        this.person = person;
    }

}

Person类

package com.ljq.entity;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;

/**
 * 人
 * 
 * @author jiqinlin
 *
 */
@Entity
@Table(name = "tb_person")
public class Person {
    @Id
    @GeneratedValue
    private Integer id;
    
    @Column(nullable = false, length = 20)
    private String name;
    
    //optional = false指明IDCard可为空
    //mappedBy="person"指明Person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="person")
    private IDCard idcard;

    public Person() {
        super();
    }

    public Person(String name) {
        super();
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public IDCard getIdcard() {
        return idcard;
    }

    public void setIdcard(IDCard idcard) {
        this.idcard = idcard;
    }

}

OneToOneTest测试类

package com.ljq.test;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

import org.junit.Test;

import com.ljq.entity.IDCard;
import com.ljq.entity.Person;

public class OneToOneTest {

    /**
     * 添加人的时候同时添加对应的身份证
     */
    @Test
    public void save() {
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();

        Person person = new Person();
        person.setName("lisi");
        IDCard idcard=new IDCard();
        idcard.setCardno("350524");
        idcard.setPerson(person);
        person.setIdcard(idcard);

        em.persist(person);

        em.getTransaction().commit();
        em.close();
        factory.close();
    }
    
    /**
     * 删除
     */
    @Test
    public void delete() {
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        
        //删除人同时会自动删除身份证
        em.remove(em.getReference(Person.class, 2));
        
        //删除身份证同时删除人
        //em.remove(em.getReference(IDCard.class, (Serializable)1));
        
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
    
    /**
     * 更新
     */
    @SuppressWarnings("unchecked")
    @Test
    public void update() {
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        
        List<Person> persons=em.createQuery("select o from Person o").getResultList();
        for(Person person:persons){
            person.setName("wangwu");
            IDCard idcard=person.getIdcard();
            if(idcard!=null){
                idcard.setCardno("abc");
            }
            em.merge(person);
        }
        
        em.getTransaction().commit();
        em.close();
        factory.close();
    }

    /**
     * 用来判断映射是否成功
     * 
     */
    @Test
    public void test() {
        Persistence.createEntityManagerFactory("ljq");
    }

}