Composite-element映射非常类似于一对多的关系映射，配置Composite-element映射，可以实现简单的一对多关系。

本例中有一个团队(team)和成员(teammembers)表，每一个team都可以拥有多个teammembers，使用Composite-element映射能够完成这种需求。

建立两个相关的数据库表：

create table team(  id int(11) not null auto_increment,  name varchar(50) default null,  primary key(id)  )engine=innodb default charset=gbk;

create table teammembers(  team_id int(11) default null,  name varchar(20) default null,  age int(3) default null,  teamrole varchar(20) default null  )engine=innodb default charset=gbk;

建立实体类Team.java：

package collect.composite_element;    import java.util.HashMap;  import java.util.Map;    public class Team implements java.io.Serializable {     // Fields     private Integer id;   private String name;   private Map memebers=new HashMap();     // Constructors     /** default constructor */   public Team() {   }     /** full constructor */   public Team(String name) {    this.name = name;   }     // 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;   }     public Map getMemebers() {    return memebers;   }     public void setMemebers(Map memebers) {    this.memebers = memebers;   }    }

建立团队成员的实体类Member.java：

package collect.composite_element;    import java.io.Serializable;    public class Member {   private String id;   private String name;   private Team team;   private String age;     public String getAge() {    return age;   }     public void setAge(String age) {    this.age = age;   }     public String getName() {    return name;   }     public void setName(String name) {    this.name = name;   }     public String getId() {    return id;   }     public void setId(String id) {    this.id = id;   }     public Team getTeam() {    return team;   }     public void setTeam(Team team) {    this.team = team;   }    }

建立一个映射文件Team.hbm.xml：

<?xml version="1.0" encoding="utf-8"?>  <!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 Persistence Tools  -->  <hibernate-mapping>   <import class="collect.composite_element.Member" />   <class name="collect.composite_element.Team" table="team"    catalog="ssh">    <id name="id" type="java.lang.Integer">     <column name="id" />     <generator class="native" />    </id>    <property name="name" type="java.lang.String">     <column name="name" length="50" />    </property>    <map name="memebers" table="teammembers">     <key column="team_id"></key>     <map-key column="teamrole" type="java.lang.String"></map-key>     <composite-element class="collect.composite_element.Member">      <parent name="team" />      <property name="name" />      <property name="age"></property>     </composite-element>    </map>   </class>  </hibernate-mapping>

“design”视图：

(注:双击所有目录节点项，都会弹出”Properties”窗口，用来设置相应属性；在单击目录节点后，在右侧的属性设置窗口也可进行相应属性的设置，非常方便)

注解：映射文件中导入(import)了Member类，使用了map集合映射，key指定了对应的key为team_id，map-key则指定了Map集合元素的索引，这里是teamrole，即团队角色(这里假定角色不能重复，即key值唯一)。通过上面“design”视图，可以清楚地看到各属性层联关系。

使用composite-element元素(嵌于<map>标签内)将Map集合中的每个元素映射给teammember的相应字段，这里映射了Member实体类。

<parent>子元素，用来表明composite-element类中的一个属性是指向包含它的实体的引用。如果在Member类中不去定义Team类型属性team及相应setter方法，运行时会出现异常：

Exception in thread "main"org.hibernate.PropertyNotFoundException: Could not find a setter for property team in classcollect.composite_element.Member

若同时去掉映射文件中的<parent>子元素以及对Team类型和相应setter方法的定义，则一切与原来一样。这也说明了JVM要通过xml文件解析编译类文件。

将该映射文件加入到Hibernate配置文件中，建立一个测试类Test.java：

package collect.composite_element;    import org.hibernate.Session;  import org.hibernate.SessionFactory;  import org.hibernate.Transaction;  import org.hibernate.cfg.Configuration;    import collect.map.UserMap;    public class Test {     public static void main(String[] args) {    // Configuration管理Hibernate配置    Configuration config = new Configuration().configure();    // 根据Configuration建立 SessionFactory    // SessionFactory用来建立Session    SessionFactory sessionFactory = config.buildSessionFactory();      // 创建实例    Team t=new Team();    t.setName("team1");        Member m1=new Member();    m1.setName("m1");    m1.setAge("33");    Member m2=new Member();    m2.setName("m2");    m2.setAge("22");        t.getMemebers().put("程序员", m1);    t.getMemebers().put("测试工程师", m2);    // 定义主键变量    Integer pid;      // 添加数据    Session session = sessionFactory.openSession();    Transaction tx = null;    try {     tx = session.beginTransaction();     // 创建主键变量     pid = (Integer) session.save(t);     tx.commit();    } catch (RuntimeException e) {     if (tx != null)      tx.rollback();     throw e;    } finally {     session.close();    }        // 修改数据    Member m3=new Member();    m3.setName("增加人员");    m3.setAge("33");    session = sessionFactory.openSession();    tx = null;    try {     tx = session.beginTransaction();     t = (Team) session.get(Team.class, pid);     // 修改名字     t.setName("team update");     t.getMemebers().put("项目经理", m3);     t.getMemebers().remove("测试工程师");     session.update(t);     tx.commit();    } catch (RuntimeException e) {     if (tx != null)      tx.rollback();     throw e;    } finally {     session.close();    }      // 查询数据    session = sessionFactory.openSession();    t = (Team) session.get(Team.class, pid);    System.out.println("team name:" + t.getName());    System.out.println("member name:" + t.getMemebers());    session.close();      // 关闭sessionFactory    sessionFactory.close();     }    }

运行结果：

控制台：

13:38:45,751 DEBUG SQL:346 -insert into ssh.team (name) values (?)

13:38:45,782 DEBUG SQL:346 -insert into teammembers (team_id, teamrole, name, age) values (?, ?, ?, ?)

13:38:45,782 DEBUG SQL:346 - insert intoteammembers (team_id, teamrole, name, age) values (?, ?, ?, ?)

数据库：

运行添加模块：

-----------------------------------------------------------------

运行修改模块：

team:

id        name

1        team update

teammembers:

team_id    name    age    teamrole

1                  m1        33      程序员

1                  m3        33      项目经理

来自:http://blog.csdn.net/itzyjr/article/details/8505830