Hibernate Composite-element投射的一个简单例子
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，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。<parent>子元素只是起说明作用，对于此例因为没有用到get/setTeam()，故可省略掉。
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