JPA一对一关联

　　这里我们仍然是使用annotation对实体进行配置。使用person与idcard模拟一对一的关联关系，一个人只能有一个ID号，同样一个ID号只能对应一个人，人与ID号是一对一的关联关系。Person类如下：

 package com.yichun.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;
 import javax.persistence.Table;

 //关系的维护端
 @Entity
 @Table(name = "person")
 public class Person {
     private Integer id;
     private String name;
     private IDCard idcard;

     public Person() {
     }

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

     @Id
     @GeneratedValue
     public Integer getId() {
         return id;
     }

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

     @Column(length = 10, nullable = false)
     public String getName() {
         return name;
     }

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

     @OneToOne(optional = false, cascade = CascadeType.ALL)//级联保存、修改、删除、同步
     @JoinColumn(name = "idcard_id")// 外键的名称idcard_id
     public IDCard getIdcard() {
     return idcard;     }         public void setIdcard(IDCard idcard) {         this.idcard = idcard;
     }
 }

IDCard类如下：

 package com.yichun.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;
 import javax.persistence.Table;

 //关系被维护端
 @Entity
 @Table(name = "idcard")
 public class IDCard {
     private Integer id;
     private String cardno;
     private Person person;

     public IDCard() {
     }

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

     @Id
     @GeneratedValue
     public Integer getId() {
         return id;
     }

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

     @Column(length = 18, nullable = false)
     public String getCardno() {
         return cardno;
     }

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

     // 出现mappedBy的就是关系被维护端,由idCard维护, optional = false可以不设置
     @OneToOne(mappedBy = "idcard", cascade = { CascadeType.PERSIST,
             CascadeType.MERGE, CascadeType.REFRESH })//CascadeType.PERSIST 级联保存,CascadeType.MERGE 级联更新,CascadeType.REFRESH 级联刷新
     public Person getPerson() {
         return person;
     }

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

保存数据

     @Test
     public void save() {
         EntityManagerFactory factory = Persistence
                 .createEntityManagerFactory("testjpa");
         EntityManager manager = factory.createEntityManager();
         manager.getTransaction().begin();

         Person person = new Person("张三");
         IDCard idCard = new IDCard("1111122222");
         person.setIdcard(idCard);
         // 1、保存person
         // 2、保存IDCard
         // 3、使用IDCard的id作为外键保存到person里面
         manager.persist(person);

         manager.getTransaction().commit();
         manager.close();
         factory.close();
     }