JPA之OneToOne关系处理

在很早学习关系数据库的时候学过一对多，多对一，一对一，多对多的关系。之前已经介绍了1对多和多对一的关系。现在来看看1对1.

业务需求：一般情况下，一个人都只有一个身份证号码（特殊情况除外）。

下面给出人和身份证实体类

 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 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})
	@JoinColumn(name="idcard_id")
	public IDCard getIdcard() {
		return idcard;
	}
	public void setIdcard(IDCard idcard) {
		this.idcard = idcard;
	}
}

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

	@OneToOne(mappedBy="idcard",cascade={CascadeType.REFRESH,CascadeType.MERGE,CascadeType.REFRESH})
	public Person getPerson() {
		return person;
	}
	public void setPerson(Person person) {
		
}

测试类

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

import org.junit.BeforeClass;
import org.junit.Test;

import cn.itcast.bean.IDCard;
import cn.itcast.bean.Person;

public class OneToOneTest {

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}
	@Test public void add(){
		 EntityManagerFactory factory = Persistence.createEntityManagerFactory("test");
		 EntityManager em = factory.createEntityManager();
		 em.getTransaction().begin(); // start transaction
		 Person person = new Person("蒋笃淅");
		 person.setIdcard(new IDCard("88888888888"));
		 em.persist(person);
		 em.getTransaction().commit(); //commit transaction
		 em.close();
		 factory.close();
	}
}

总结：1对1其实可以参考1对多进行考虑，它的关系维护端由编写者自己去定义。