Hibernate：一对一（1）-优快云博客

本文介绍Hibernate框架中实现一对一关联关系的方法，通过使用主键关联的方式，展示了Person与IdCart两个实体类之间的映射关系，并提供了相应的测试代码。

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Hibernate中一对一关联两种处理方式之一：参照表主键参照被参照表主键

POJO对象

被参照对象

public class Person {

	private Integer id;
	private String name;
	private IdCart idCart;


	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public IdCart getIdCart() {
		return idCart;
	}
	public void setIdCart(IdCart cart) {
		idCart = cart;
	}
}

参照对象

public class IdCart {

	private Integer id;
	private String userFullTime;
	private Person person;

	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getUserFullTime() {
		return userFullTime;
	}
	public void setUserFullTime(String userFullTime) {
		this.userFullTime = userFullTime;
	}
	public Person getPerson() {
		return person;
	}
	public void setPerson(Person person) {
		this.person = person;
	}
}

映射文件：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.itcast.hibernate.domain">

	<class name="Person">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="name"/>
		<one-to-one name="idCart"/>
	</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.itcast.hibernate.domain">

	<class name="IdCart" table="cart">
		<id name="id" unsaved-value="-1">
			<generator class="foreign">
				<param name="property">person</param>
			</generator>
		</id>
		<property name="userFullTime"/>
		<one-to-one name="person" constrained="true"/>
	</class>
</hibernate-mapping>

测试代码：

public class OneToOneTest {

	public static void main(String[] args) {
		Session session = HibernateUtil.getSession();
		Transaction tx = session.beginTransaction();

		Person person = new Person();
		person.setName("张三");

		IdCart iCart = new IdCart();
		iCart.setUserFullTime("29年");

		iCart.setPerson(person);
		person.setIdCart(iCart);

		session.save(person);
		session.save(iCart);

		Person person1 = (Person)session.get(Person.class, 1);
		System.out.println(person1.getName());

		//IdCart idCart = person1.getIdCart();
		//System.out.println(idCart.getUserFullTime());


		tx.commit();
	}

}

注意：不管是否利用关联访问被参照对象，还是参照对象的信息，都会两个表联合查询，输出的sql语句如下：

既是先访问那个对象也一样：

		IdCart idCart = (IdCart)session.get(IdCart.class, 2);
		System.out.println(idCart.getUserFullTime());

		Person person2 = idCart.getPerson();
		System.out.println(person2.getName());

[code="java"]Hibernate:
select
person0_.id as id2_1_,
person0_.name as name2_1_,
idcart1_.id as id3_0_,
idcart1_.userFullTime as userFull2_3_0_
from
Person person0_
left outer join
cart idcart1_
on person0_.id=idcart1_.id
where
person0_.id=?code]

只是一条查询语句，左外连接{一对一和多对一及一对多查询不同！！！}既是没有输出及没有调用p.getIdCard()也是做外连接！！！！！！！！但是如果只是查询从从表的对象那只是一个简单的查询！！！！！！！！