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");    }}