Hibernate一对多数据关联

一对多数据关联

一.单向一对多数据关联
一个用户有多个地址，在用户类TUser中包含地址类TAddress集合。

1.数据模型

2.表定义sql

use sample;

DROP TABLE T_Address;
DROP TABLE T_User;

CREATE TABLE T_User (
       id INT NOT NULL AUTO_INCREMENT
     , name VARCHAR(50)
     , age INT
     , PRIMARY KEY (id)
);

CREATE TABLE T_Address (
       id INT NOT NULL AUTO_INCREMENT
     , address VARCHAR(200)
     , zipcode VARCHAR(10)
     , tel VARCHAR(20)
     , type VARCHAR(20)
     , user_id INT NOT NULL
     , idx INT
     , PRIMARY KEY (id)
     , INDEX (user_id)
     , CONSTRAINT FK_T_Address_1 FOREIGN KEY (user_id)
                  REFERENCES T_User (id)
);

3.POJO类
TUser.java

package cn.blogjava.start;

import java.util.Set;

public class TUser  implements java.io.Serializable {
    // Fields
     private Integer id;
     private Integer age;
     private String name;
     private Set address;

    // Constructors

    public Integer getAge() {
        return age;
    }

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

    public Set getAddress() {
        return address;
    }

    public void setAddress(Set address) {
        this.address = address;
    }

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

    /** constructor with id */
    public TUser(Integer id) {
        this.id = id;
    }

    // Property accessors

    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

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

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

TAddress.java

package cn.blogjava.start;

import java.io.Serializable;

public class TAddress implements Serializable {

    private Integer id;
    private String address;
    private String zipcode;
    private String tel;
    private String type;
    private Integer userId;
    private Integer idx;

    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public Integer getIdx() {
        return idx;
    }
    public void setIdx(Integer idx) {
        this.idx = idx;
    }
    public String getTel() {
        return tel;
    }
    public void setTel(String tel) {
        this.tel = tel;
    }
    public String getType() {
        return type;
    }
    public void setType(String type) {
        this.type = type;
    }
    public Integer getUserId() {
        return userId;
    }
    public void setUserId(Integer userId) {
        this.userId = userId;
    }
    public String getZipcode() {
        return zipcode;
    }
    public void setZipcode(String zipcode) {
        this.zipcode = zipcode;
    }

}

3.配置文件
TUser.hbm.xml

<?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>
    <class name="cn.blogjava.start.TUser" table="T_User" catalog="sample"
     dynamic-update="true" dynamic-insert="true"
    >
        <id name="id" type="integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="string" column="name" />
        <property name="age" type="java.lang.Integer" column="age" />

        <set name="address" table="t_address" cascade="all" order-by="zipcode asc">
            <key column="user_id">
            </key>
            <one-to-many class="cn.blogjava.start.TAddress" />
        </set>
    </class>
</hibernate-mapping>

TAddress.hbm.xml
注意：没有配置user_id字段。

4.测试代码

package cn.blogjava.start;

import java.util.HashSet;
import java.util.Iterator;
import java.util.List;

import junit.framework.Assert;
import junit.framework.TestCase;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class HibernateTest extends TestCase {

    Session session = null;

    protected void setUp() {
        try {
            Configuration config = new Configuration().configure();
            SessionFactory sessionFactory = config.buildSessionFactory();
            session = sessionFactory.openSession();

        } catch (HibernateException e) {
            e.printStackTrace();
        }
    }

    protected void tearDown() {
        try {
            session.close();
        } catch (HibernateException e) {
            e.printStackTrace();
        }
    }

    /**
     * 对象持久化测试(Insert方法)
     */
    public void testInsert() {
        Transaction tran = null;
        try {

            TUser user = new TUser();
            user.setName("byf");
            user.setAge(new Integer(26));

            TAddress addr = new TAddress();
            addr.setTel("1123");
            addr.setZipcode("233123");
            addr.setAddress("HongKong");

            TAddress addr2 = new TAddress();
            addr2.setTel("139");
            addr2.setZipcode("116001");
            addr2.setAddress("dalian");

            TAddress addr3 = new TAddress();
            addr3.setTel("136");
            addr3.setZipcode("100080");
            addr3.setAddress("beijing");

            //设置关联
            HashSet set = new HashSet();
            set.add(addr);
            set.add(addr2);
            set.add(addr3);
            user.setAddress(set);

            tran = session.beginTransaction();
            //插入user信息
            session.save(user);
            session.flush();
            tran.commit();
            Assert.assertEquals(user.getId().intValue()>0 ,true);
        } catch (HibernateException e) {
            e.printStackTrace();
            Assert.fail(e.getMessage());
            if(tran != null) {
                try {
                    tran.rollback();
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            }
        }
    }

    /**
     * 对象读取测试(Select方法)
     */
    public void testSelect(){
        String hql = " from TUser where name='byf'";
        try {
            List userList = session.createQuery(hql).list();
            TUser user = (TUser)userList.get(0);
            System.out.println("user name is " + user.getName());

            for (Iterator iter = user.getAddress().iterator(); iter.hasNext();) {
                TAddress addr = (TAddress) iter.next();
                System.out.println("user address is " + addr.getAddress());
            }
            Assert.assertEquals(user.getName(), "byf");
        } catch (Exception e) {
            e.printStackTrace();
            Assert.fail(e.getMessage());
        }
    }
}

说明:
一个问题，由于是单向关联，为了保持关联关系，我们只能通过主控方对被动方进行级联更新。如果被关联方的字段为NOT NULL属性，当Hibernate创建或者更新关联关系时，可能出现约束违例。
例子中T_Address表中的user_id 为NOT NULL，如果在TAddress.hbm.xml映射了全部字段时。创建一个用户并赋予她地址信息，对于T_Address表而言，hibernate会执行两条sql语句来保存地址信息。

要执行两条SQL语句，是因为关联是单向的，就是说对于TAddress对象而言，并不知道自己应该与那一个TUser对象关联，只能先将user_id设为一个空值。
之后，根据配置文件
        <set name="address" table="t_address" cascade="all" order-by="zipcode asc">
            <key column="user_id">
            </key>
            <one-to-many class="cn.blogjava.start.TAddress" />
        </set>
由TUser对象将自身的id赋给addr.user_id，这样导致addr属性值变动，在事物提交的时候，会进行update。

1)当save该用户的时候，
insert into t_address (user_id, address, zipcode, tel) value (null, "HongKong", "233123", "1123")

2)当tx.commit()时：
update t_address user_id="1", address="HongKong", zipcode="233123",tel="1123" where id=2;

这样，在save user时，就会出现约束违例。

调整方法：
可以在定义数据表字段时候，不加NOT NULL约束。或者在开始为user_id随意赋一个非空值(因为还要update，不正确也没关系)，或者将user_id字段从TAddress.hbm.xml中删除(本例就是这样实现)。

但是这些都是权宜之计，用两条SQL语句完成一次数据库操作，性能低下。
而双向一对多解决了这个问题。
下面来实现双向关联：
修改配置文件
TUser.hbm.xml

<?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>
    <class name="cn.blogjava.start.TUser" table="T_User" catalog="sample"
     dynamic-update="true" dynamic-insert="true"
    >
        <id name="id" type="integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="string" column="name" />
        <property name="age" type="java.lang.Integer" column="age" />

        <set
            name="address"
            table="t_address"
            inverse="true"
            cascade="all"
            order-by="zipcode asc"
            >
            <key column="user_id">
            </key>
            <one-to-many class="cn.blogjava.start.TAddress" />
        </set>
    </class>
</hibernate-mapping>

设定inverse="true",表明将TUser类作为被动类，将数据关联的维护工作交给关联对象TAddress来管理。
在one-to-many模型中，将many一方设为主控方有助于性能的改善。(让总理记住每个人困难，但是每个人记住总理方便)

TAddress.hbm.xml

<?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>
    <class name="cn.blogjava.start.TAddress" table="T_Address" catalog="sample">
        <id name="id" type="integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="address" type="string" column="address" />
        <property name="zipcode" type="string" column="zipcode" />
        <property name="tel" type="string" column="tel" />
        <property name="type" type="string" column="type" />
        <property name="idx" type="java.lang.Integer" column="idx" />
        <many-to-one
                  name="user"
                  class="cn.blogjava.start.TUser"
                  cascade="none"
                  outer-join="auto"
                  update="true"
                  insert="true"
                  access="property"
                  column="user_id"
                  not-null="true"
        />
    </class>
</hibernate-mapping>

2.对TAddress.java做如下改造：
去掉user_id字段，增加user字段，和getter,setter方法。

package cn.blogjava.start;

import java.io.Serializable;

public class TAddress implements Serializable {

    private Integer id;
    private String address;
    private String zipcode;
    private String tel;
    private String type;
    private Integer idx;
    private TUser user;

    public TUser getUser() {
        return user;
    }
    public void setUser(TUser user) {
        this.user = user;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public Integer getIdx() {
        return idx;
    }
    public void setIdx(Integer idx) {
        this.idx = idx;
    }
    public String getTel() {
        return tel;
    }
    public void setTel(String tel) {
        this.tel = tel;
    }
    public String getType() {
        return type;
    }
    public void setType(String type) {
        this.type = type;
    }
    public String getZipcode() {
        return zipcode;
    }
    public void setZipcode(String zipcode) {
        this.zipcode = zipcode;
    }

}

4.测试代码
既然TUser不维护关联关系，需要TAddress需要自己来维护TUser，所以需要addr.setUser(user);

package cn.blogjava.start;

import java.util.HashSet;

import java.util.Iterator;

import java.util.List;

import junit.framework.Assert;

import junit.framework.TestCase;

import org.hibernate.HibernateException;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

public class HibernateTest extends TestCase {

Session session = null;

protected void setUp() {

try {

Configuration config = new Configuration().configure();

SessionFactory sessionFactory = config.buildSessionFactory();

session = sessionFactory.openSession();

} catch (HibernateException e) {

e.printStackTrace();

}

protected void tearDown() {

try {

session.close();

} catch (HibernateException e) {

e.printStackTrace();

}

/**

* 对象持久化测试(Insert方法)

public void testInsert() {

Transaction tran = null;

try {

TUser user = new TUser();

user.setName("byf");

user.setAge(new Integer(26));

TAddress addr = new TAddress();

addr.setTel("1123");

addr.setZipcode("233123");

addr.setAddress("HongKong");

addr.setUser(user);

TAddress addr2 = new TAddress();

addr2.setTel("139");

addr2.setZipcode("116001");

addr2.setAddress("dalian");

addr2.setUser(user);

TAddress addr3 = new TAddress();

addr3.setTel("136");

addr3.setZipcode("100080");

addr3.setAddress("beijing");

addr3.setUser(user);

//设置关联

HashSet set = new HashSet();

set.add(addr);

set.add(addr2);

set.add(addr3);

user.setAddress(set);

tran = session.beginTransaction();

//插入user信息

session.save(user);

session.flush();

tran.commit();

Assert.assertEquals(user.getId().intValue()>0 ,true);

} catch (HibernateException e) {

e.printStackTrace();

Assert.fail(e.getMessage());

if(tran != null) {

try {

tran.rollback();

} catch (Exception e1) {

e1.printStackTrace();

}

/**

* 对象读取测试(Select方法)

public void testSelect(){

String hql = " from TUser where name='byf'";

try {

List userList = session.createQuery(hql).list();

TUser user = (TUser)userList.get(0);

System.out.println("user name is " + user.getName());

for (Iterator iter = user.getAddress().iterator(); iter.hasNext();) {

TAddress addr = (TAddress) iter.next();

System.out.println("user address is " + addr.getAddress());

}

Assert.assertEquals(user.getName(), "byf");

} catch (Exception e) {

e.printStackTrace();

Assert.fail(e.getMessage());

}

posted on 2006-07-05 15:13 knowhow 阅读(549) 评论(1) 编辑收藏所属分类: ORM：Hibernate及其他

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