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"); }}