Hibernate映射一对一关联(之一)

单向一对一是单向多对一的一种特殊情况，可以使用单向多对一实现。只要在多的一面，指定unique="true"，即可，例如在学生的映射文件中配置：

<many-to-one name="teacher"
            column="id"
            class="org.shirdrn.entity.Teacher"
            insert="false"
            update="false"
            cascade="all"
            unique="true">
        </many-to-one>

说明一个学生对应一个教师，这里如果教师的类型是家庭教师，教师对学生也是一对一关联。

下面做个测试的例子：

建立数据库hibernate，表person和card，即人和身份证，表的结构如图所示：

person表：

 

card表：

 

第一种方式：使用one-to-many或者many-to-one配置一对一关联

先看一下一对一单向关联（以Person与Card的关联为例，即在Person一方配置与Card的关联）：

映射文件及其POJO如下：

Person.hbm.xml和Person.java分别如下：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
<hibernate-mapping>
    <class name="org.shirdrn.entity.Person" table="person" schema="dbo" catalog="hibernate">
        <id name="id" type="java.lang.String">
            <column name="id" length="50" />
            <generator class="assigned" />
        </id>
        <many-to-one name="card"
            class="org.shirdrn.entity.Card"
            update="false"
            insert="false"
            cascade="save-update">
            <column name="id" length="50" not-null="true" unique="true" />
        </many-to-one>
        <property name="name" type="java.lang.String">
            <column name="name" length="50" not-null="true" />
        </property>
        <property name="gender" type="java.lang.String">
            <column name="gender" length="10" />
        </property>
        <property name="age" type="java.lang.Integer">
            <column name="age" />
        </property>
        <property name="addr" type="java.lang.String">
            <column name="addr" length="50" />
        </property>
    </class>
</hibernate-mapping>

 

package org.shirdrn.entity;

/**
* Person generated by MyEclipse - Hibernate Tools
*/

public class Person implements java.io.Serializable {
    // Fields   

     private String id;
     private Card card;
     private String name;
     private String gender;
     private Integer age;
     private String addr;

    // Constructors

    /** default constructor */
    public Person() {
    }

/** minimal constructor */
    public Person(String id, Card card, String name) {
        this.id = id;
        this.card = card;
        this.name = name;
    }
   
    /** full constructor */
    public Person(String id, Card card, String name, String gender, Integer age, String addr) {
        this.id = id;
        this.card = card;
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.addr = addr;
    }

  
    // Property accessors

    public String getId() {
        return this.id;
    }
   
    public void setId(String id) {
        this.id = id;
    }

    public Card getCard() {
        return this.card;
    }
   
    public void setCard(Card card) {
        this.card = card;
    }

    public String getName() {
        return this.name;
    }
   
    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return this.gender;
    }
   
    public void setGender(String gender) {
        this.gender = gender;
    }

    public Integer getAge() {
        return this.age;
    }
   
    public void setAge(Integer age) {
        this.age = age;
    }

    public String getAddr() {
        return this.addr;
    }
   
    public void setAddr(String addr) {
        this.addr = addr;
    }
}

Card.hbm.xml和Card.java分别如下：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
<hibernate-mapping>
    <class name="org.shirdrn.entity.Card" table="card" schema="dbo" catalog="hibernate">
        <id name="id" type="java.lang.String">
            <column name="id" length="50" />
            <generator class="assigned" />
        </id>
        <property name="cardNo" type="java.lang.String">
            <column name="cardNo" length="50" not-null="true" />
        </property>
        <property name="releaseTime" type="java.util.Date">
            <column name="releaseTime" length="23" not-null="true" />
        </property>
        <property name="releaseArea" type="java.lang.String">
            <column name="releaseArea" length="10" not-null="true" />
        </property>
        <property name="effectTime" type="java.lang.Integer">
            <column name="effectTime" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

package org.shirdrn.entity;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

/**
* Card generated by MyEclipse - Hibernate Tools
*/

public class Card implements java.io.Serializable {

    // Fields   

     private String id;
     private String cardNo;
     private Date releaseTime;
     private String releaseArea;
     private Integer effectTime;

    // Constructors

    /** default constructor */
    public Card() {
    }

/** minimal constructor */
    public Card(String id, String cardNo, Date releaseTime, String releaseArea, Integer effectTime) {
        this.id = id;
        this.cardNo = cardNo;
        this.releaseTime = releaseTime;
        this.releaseArea = releaseArea;
        this.effectTime = effectTime;
    }

  
    // Property accessors

    public String getId() {
        return this.id;
    }
   
    public void setId(String id) {
        this.id = id;
    }

    public String getCardNo() {
        return this.cardNo;
    }
   
    public void setCardNo(String cardNo) {
        this.cardNo = cardNo;
    }

    public Date getReleaseTime() {
        return this.releaseTime;
    }
   
    public void setReleaseTime(Date releaseTime) {
        this.releaseTime = releaseTime;
    }

    public String getReleaseArea() {
        return this.releaseArea;
    }
   
    public void setReleaseArea(String releaseArea) {
        this.releaseArea = releaseArea;
    }

    public Integer getEffectTime() {
        return this.effectTime;
    }
   
    public void setEffectTime(Integer effectTime) {
        this.effectTime = effectTime;
    }
}

在Person.hbm.xml中配置了many-to-one，unique="true"说明是一对一单向关联，而且 cascade="save-update"，级联存储更新。

测试程序如下：

package org.shirdrn.test;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.shirdrn.HibernateSessionFactory;
import org.shirdrn.entity.Card;
import org.shirdrn.entity.Person;

public class MyTest {
public static void main(String[] args){
   Session session = HibernateSessionFactory.getSession();
   Transaction tx = null;
   try{
    tx = session.beginTransaction();
    Person p = new Person();
    p.setId("222403199901011113");
    p.setName("刘备");
    Card c = new Card();
    c.setId("222403199901011113");
    c.setCardNo("JL-2008-03-04-0001");
    c.setReleaseTime(new Date());
    c.setReleaseArea("长春");
    c.setEffectTime(new Integer(20));
    p.setCard(c);
    session.save(p);
    tx.commit();
   }
   catch(Exception e){
    tx.rollback();
    e.printStackTrace();
   }
   finally{
    HibernateSessionFactory.closeSession();
   }
}

}

查看结果如下：

Hibernate: select card_.id, card_.cardNo as cardNo3_, card_.releaseTime as releaseT3_3_, card_.releaseArea as releaseA4_3_, card_.effectTime as effectTime3_ from hibernate.dbo.card card_ where card_.id=?
Hibernate: insert into hibernate.dbo.card (cardNo, releaseTime, releaseArea, effectTime, id) values (?, ?, ?, ?, ?)
Hibernate: insert into hibernate.dbo.person (name, gender, age, addr, id) values (?, ?, ?, ?, ?)

执行了两次insert操作，存储数据成功。

反过来，在Card.hbm.xml中配置与Person的关联，如果使用many-to-one配置一对一单向关联，过程和上面的是一样的。

现在我们使用one-to-many配置一对一单向关联：

其实，在我们指定了“多”的一方的时候（如Card），如果没有限制的话（比如这里要求配置一对一），它对于“一”的一方来说就是一对一或者一对多，无论是在“一”的一方配置一对一或者一对多，对单向关联都没有影响，因为“多”的一方可以单条记录操作（如果是一对一），也可以多条记录操作（如果是一对多），参照的就是另一方。

在上面的基础上，把Person.hbm.xml中的

<many-to-one name="card"
            class="org.shirdrn.entity.Card"
            update="false"
            insert="false"
            cascade="save-update">
            <column name="id" length="50" not-null="true" unique="true" />
</many-to-one>

去掉，改为在card.hbm.xml中配置one-to-many如下：

<set name="persons"
        inverse="true"
        cascade="save-update">
            <key>
                <column name="id" length="50" not-null="true" unique="true" />
            </key>
            <one-to-many class="org.shirdrn.entity.Person" />
</set>

并且，要在Card的POJO里面添加Field：

private Set persons = new HashSet(0);

以及：

public Set getPersons() {
        return this.persons;
}
    
public void setPersons(Set persons) {
        this.persons = persons;
   }

测试程序如下：

package org.shirdrn.test;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.shirdrn.HibernateSessionFactory;
import org.shirdrn.entity.Card;
import org.shirdrn.entity.Person;

public class MyTest {
public static void main(String[] args){
   Session session = HibernateSessionFactory.getSession();
   Transaction tx = null;
   try{
    tx = session.beginTransaction();
    Person p = new Person();
    p.setId("222403199901011116");
    p.setName("刘备");
    Set hs = new HashSet();
    hs.add(p);
    Card c = new Card();
    c.setId("222403199901011116");
    c.setCardNo("JL-2008-03-04-0001");
    c.setReleaseTime(new Date());
    c.setReleaseArea("长春");
    c.setEffectTime(new Integer(20));
    p.setCard(c);
    c.setPersons(hs);
    session.save(c);
    tx.commit();
   }
   catch(Exception e){
    tx.rollback();
    e.printStackTrace();
   }
   finally{
    HibernateSessionFactory.closeSession();
   }
}

}

执行结果如下：

Hibernate: select person_.id, person_.name as name2_, person_.gender as gender2_, person_.age as age2_, person_.addr as addr2_ from hibernate.dbo.person person_ where person_.id=?
Hibernate: insert into hibernate.dbo.card (cardNo, releaseTime, releaseArea, effectTime, id) values (?, ?, ?, ?, ?)
Hibernate: insert into hibernate.dbo.person (name, gender, age, addr, id) values (?, ?, ?, ?, ?)

级联保存成功。

这里，是先把要insert的数据set到Person对象中，然后把Person对象放到HashSet中，通过配置的集合映射及其关联，把存有Person对象的HashSet正确地set到Card的对象中，然后可以insert我们处理过的Card对象了，而且级联insert了Card对象。