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;50     }   51 52     public void setIdcard(IDCard idcard) {53         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();
    }