JPA---一对一关系

在JPA中，使用@oneToOne来标示。

package com.yl.demo1.bean.oneToone;

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;

@Entity
public class User {
    private Integer id;
    private String name;
    private IDCard idcard;
    
    public User(){}
    
    public User(String name) {
        super();
        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)
    @JoinColumn(name="idcard_id")
    public IDCard getIdcard() {
        return idcard;
    }
    public void setIdcard(IDCard idcard) {
        this.idcard = idcard;
    }
    
    
}

 1 package com.yl.demo1.bean.oneToone;
 2 
 3 import javax.persistence.CascadeType;
 4 import javax.persistence.Column;
 5 import javax.persistence.Entity;
 6 import javax.persistence.GeneratedValue;
 7 import javax.persistence.Id;
 8 import javax.persistence.OneToOne;
 9 
10 @Entity
11 public class IDCard {
12     private Integer id;
13     private String cardno;
14     private User user;
15     
16     public IDCard(){}
17     
18     public IDCard(String cardno) {
19         super();
20         this.cardno = cardno;
21     }
22     @Id @GeneratedValue
23     public Integer getId() {
24         return id;
25     }
26     public void setId(Integer id) {
27         this.id = id;
28     }
29     @Column(length=18, nullable=false)
30     public String getCardno() {
31         return cardno;
32     }
33     public void setCardno(String cardno) {
34         this.cardno = cardno;
35     }
36     /**
37      * 在一对一的关系中，出现mappedBy的对象为关系的被维护端
38      * 
39      */
40     @OneToOne(mappedBy="idcard", cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})
41     public User getUser() {
42         return user;
43     }
44     public void setUser(User user) {
45         this.user = user;
46     }
47     
48     
49 }

常见操作：

 1 @Test
 2     public void save() {
 3         EntityManagerFactory factory = Persistence.createEntityManagerFactory("YL");
 4         EntityManager em = factory.createEntityManager();
 5         em.getTransaction().begin();//事务开始
 6         
 7         User user = new User("ylll");
 8         user.setIdcard(new IDCard("123456789012345678"));
 9         
10         em.persist(user);
11         
12         em.getTransaction().commit();
13         em.close();
14         factory.close();
15     }