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();
    }