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;
    }

}

 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.OneToOne;

 @Entity
 public class IDCard {
     private Integer id;
     private String cardno;
     private User user;

     public IDCard(){}

     public IDCard(String cardno) {
         super();
         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;
     }
     /**
      * 在一对一的关系中，出现mappedBy的对象为关系的被维护端
      *
      */
     @OneToOne(mappedBy="idcard", cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})
     public User getUser() {
         return user;
     }
     public void setUser(User user) {
         this.user = user;
     }

 }

常见操作：

 @Test
     public void save() {
         EntityManagerFactory factory = Persistence.createEntityManagerFactory("YL");
         EntityManager em = factory.createEntityManager();
         em.getTransaction().begin();//事务开始

         User user = new User("ylll");
         user.setIdcard(new IDCard("123456789012345678"));

         em.persist(user);

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