5.6.4 映射集合属性:List集合属性

hibernate.cfg.xml :

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

    <session-factory>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/test</property>
        <property name="connection.username">root</property>
        <property name="connection.password">mysqladmin</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hbm2ddl.auto">update</property>
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <mapping resource="db/mapping/Person.hbm.xml"/>
    </session-factory>

</hibernate-configuration>

Person.java :

public class Person {
	
	private int id;
	private String name;
	private int age;
	private List<String> schools=new ArrayList<String>();
	
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public List<String> getSchools() {
		return schools;
	}
	public void setSchools(List<String> schools) {
		this.schools = schools;
	}
	
}

Person.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 package="db.domain">
    <class name="Person" table="persons">
    
        <id name="id" type="integer">
            <generator class="native"/>
        </id>
        <property name="name" type="string">
            <column name="name"></column>
        </property>
        <property name="age" type="integer">
            <column name="age"></column>
        </property>

        <list name="schools" table="schools">         <!--用list元素-->
            <key column="person_id" not-null="true"/>
            <list-index column="schools_list_order"/>
            <element type="string" column="school_name"/>
        </list>
        
    </class>
</hibernate-mapping>

Test.java :

public class Test {

	public static void main(String[] args) {

		Person p1=new Person();
		p1.setName("tom");
		p1.setAge(20);
		List<String> schools1=new ArrayList<String>();
		schools1.add("小学");
		schools1.add("初中");
		schools1.add("高中");
		p1.setSchools(schools1);
		
		Person p2=new Person();
		p2.setName("jack");
		p2.setAge(23);
		List<String> schools2=new ArrayList<String>();
		schools2.add("小学");
		schools2.add("初中");
		schools2.add("高中");
		schools2.add("大学");
		p2.setSchools(schools2);
		
		Session session=HibernateSessionFactory.getSession();
		Transaction txt=session.beginTransaction();
		session.save(p1);
		session.save(p2);
		txt.commit();
		HibernateSessionFactory.closeSession();
	}

}

运行Test.java后，查看数据库：

对于同一个持久化对象而言，它所包含的集合元素的索引是不会重复的，因此List集合属性可以用关联持久化对象的外键和集合索引列作为联合主键。参看上图。

对于List集合属性，应该使用<List.../>元素完成映射，它有三个子元素：

<List.../>的子元素

名称	说明
<key.../>	集合属性的值不可能与持久化类存储在同一个表内，集合属性会存放在另外的表中， 因此必须以外键关联，所以需要增加<key.../>元素来映射该外键列。
<list-index.../>	映射List集合的索引列。
<element.../>	当集合元素是基本类型及其包装类、字符串类型和日期类型时使用该元素。