JPA学习---第十节：JPA中的一对一双向关联

1、创建实体类，代码如下：

代码清单1：

package learn.jpa.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;

@Entity
public class Person {

    private int id;
    private String name;
    private IDCard idcard;

    public Person(){

    }

    public Person(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;
    }
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

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

代码清单2：

package learn.jpa.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;

@Entity
public class IDCard {

    private int id;
    private String cardno;
    private Person person;

    public IDCard(){

    }

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

    @OneToOne(mappedBy="idcard",cascade={CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REFRESH},
            optional=false)
    public Person getPerson() {
        return person;
    }
    public void setPerson(Person person) {
        this.person = person;
    }
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

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

}

2、测试代码：

package learn.jpa.test;

import static org.junit.Assert.*;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

import learn.jpa.entity.IDCard;
import learn.jpa.entity.Person;

import org.junit.Test;

public class OneToOneTest {

    /**
     * 测试数据库是否可以生成表
     */
    @Test
    public void test() {
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        factory.close();
    }

    @Test
    public void save(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();   // 开启事务

        Person person = new Person("hwl");
        IDCard idcard = new IDCard("435034189809170123");
        idcard.setPerson(person);
        person.setIdcard(idcard);
        em.persist(person);
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
}