dldj_066_hibernate关联关系映射_双向关联

一、一对多关联关系映射(双向关联)

　　一对多关联关系站在一方角度考虑是一对多、站在多方角度考虑是多对一

　　一个国家(Country)有多个部长(Minister)、一个部长只属于一个国家

　　1.1Country类、及其映射文件Country.hbm.xml　　

package edu.aeon.beans;

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

/**
 * [说明]:Country(国家)实体类
 * @author aeon
 *
 */
public class Country {
    /**国家id*/
    private Integer cid;
    /**国家名*/
    private String cname;
    /**一个国家里部长集合*/
    private Set<Minister> ministers;
    public Country() {
        super();
        //初始化
        ministers=new HashSet<Minister>();
    }
    public Country(String cname) {
        this();
        this.cname = cname;
    }

    public Integer getCid() {
        return cid;
    }
    public void setCid(Integer cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Set<Minister> getMinisters() {
        return ministers;
    }
    public void setMinisters(Set<Minister> ministers) {
        this.ministers = ministers;
    }
    @Override
    public String toString() {
        return "Country [cid=" + cid + ", cname=" + cname + ", minister=" + ministers + "]";
    }
}

Country.hbm.xml

　　

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="edu.aeon.beans">
    <class name="Country">
        <id name="cid">
            <column name="cid" sql-type="int(3)"/>
            <generator class="native"/>
        </id>
        <property name="cname">
            <column name="cname" sql-type="varchar(16)"/>
        </property>
        <!-- 关联属性的映射配置 -->
        <!-- name:关联属性的属性名 -->
        <set name="ministers" cascade="save-update">
            <!-- 关联的外键 -->
            <key column="countryid" />
            <!-- 关联到那个类 -->
            <one-to-many class="Minister"/>
        </set>
    </class>
</hibernate-mapping>

　　1.2Minister及其映射文件Minister.hbm.xml　　

package edu.aeon.beans;
/**
 * [说明]:minister(部长)实体类
 * @author aeon
 *
 */
public class Minister {
    /**部长id*/
    private Integer mid;
    /**部长名*/
    private String mname;
    /**属于的国家*/
    private Country country;
    
    public Minister() {

    }
    public Minister(String mname) {
        super();
        this.mname = mname;
    }
    
    public Integer getMid() {
        return mid;
    }
    public void setMid(Integer mid) {
        this.mid = mid;
    }
    public String getMname() {
        return mname;
    }
    public void setMname(String mname) {
        this.mname = mname;
    }
    
    
    public Country getCountry() {
        return country;
    }
    public void setCountry(Country country) {
        this.country = country;
    }
    @Override
    public String toString() {
        return "Minister [mid=" + mid + ", mname=" + mname + "]";
    }
}

Minister.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="edu.aeon.beans">
    <class name="Minister">
        <id name="mid">
            <column name="mid" sql-type="int(3)"/>
            <generator class="native"/>
        </id>
        <property name="mname">
            <column name="mname" sql-type="varchar(16)"/>
        </property>
        <!-- 
        站在自己(minister)的角度属于多对一 
        name="country":关联的属性名
        class="Country":关联的属性类型
        cascade="save-update":设置级联保存方式保存己方的同时更新对方表
        column name="countryid":代表关联的主键    
        -->
        <many-to-one name="country" class="Country" cascade="save-update">
            <column name="countryid"/>
        </many-to-one>
    </class>
</hibernate-mapping>

然后将这两个实体类对应的映射信息注册到主配置文件(hibernate.cfg.xml)当中：

　　

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- 配置数据库的四要素 -->
        <property name="hibernate.connection.driver">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/db_test</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">root</property>
        <!-- 配置数据库方言 -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <!-- 配置数据库连接池 -->
        <!-- <property name="hibernate.connection.provider_class">org.hibernate.c3p0.internal.C3P0ConnectionProvider</property> -->
        <!-- 注册当前session上下文 -->
        <property name="hibernate.current_session_context_class">thread</property>
        <!-- 自动建表 -->
        <property name="hibernate.hbm2ddl.auto">update</property>
        <!-- 显示sql -->
        <property name="hibernate.show_sql">true</property>
        <!-- 格式化sql -->
        <property name="hibernate.format_sql">true</property>
        <mapping resource="edu/aeon/beans/Country.hbm.xml"/>
        <mapping resource="edu/aeon/beans/Minister.hbm.xml"/>
        <!-- <mapping resource="sqlMapping.xml"/> -->
    </session-factory>
</hibernate-configuration>    

1.3测试类

　　

package edu.aeon.hibernate.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;
import edu.aeon.aeonutils.hibernate.getsessionutil.GetSessionUtil;
import edu.aeon.beans.Country;
import edu.aeon.beans.Minister;

/**
 * [说明]:测试类
 * @author aeon
 *
 */
public class HibernateTest {
    /**
     * 测试1对多关联关系
     */
    @Test
    public  void testOne2Many(){
        Session session=null;
        Transaction transaction=null;
        try {
            session = GetSessionUtil.getSession();
            System.out.println(session);
            transaction = session.getTransaction();
            System.out.println(transaction);
            transaction.begin();
            //Country维护关联关系
            /*Minister minister1=new Minister("部长甲");
            Minister minister2=new Minister("部长乙");
            Country country=new Country("china");
            country.getMinisters().add(minister1);
            country.getMinisters().add(minister2);
            session.save(country);*/
            //Minister维护关联关系、谁维护保存谁
            Minister minister1=new Minister("张部长");
            Country country=new Country("中国");
            minister1.setCountry(country);
            session.save(minister1);
            transaction.commit();
        } catch (Exception e) {
            transaction.rollback();
            e.printStackTrace();
        }
    }
}

测试结果控制台输出：

　　

Hibernate: 
    
    create table Country (
        cid int(3) not null auto_increment,
        cname varchar(16),
        primary key (cid)
    )
Hibernate: 
    
    create table Minister (
        mid int(3) not null auto_increment,
        mname varchar(16),
        countryid integer,
        primary key (mid)
    )
Hibernate: 
    
    alter table Minister 
        add constraint FKc9dntt9ob26y2m3b5ydae4dva 
        foreign key (countryid) 
        references Country (cid)
ThreadLocalSessionContext.TransactionProtectionWrapper[SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=ExecutableList{size=0} updates=ExecutableList{size=0} deletions=ExecutableList{size=0} orphanRemovals=ExecutableList{size=0} collectionCreations=ExecutableList{size=0} collectionRemovals=ExecutableList{size=0} collectionUpdates=ExecutableList{size=0} collectionQueuedOps=ExecutableList{size=0} unresolvedInsertDependencies=null])]
org.hibernate.engine.transaction.internal.TransactionImpl@508c825
Hibernate: 
    insert 
    into
        Country
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        Minister
        (mname, countryid) 
    values
        (?, ?)

本次用到的工具类GetSessionUtil.java前面已经附上了。