Hibernate学习43 -- 抓取策略3 -- 子查询抓取

fetch="subselect",另外发送一条select语句抓取在前面查询到的所有实体对象的关联集合。例如：<set name="students" inverse="true" cascade="all" fetch="subselect">

例子代码如下：

Classes.hbm.xml <hibernate-mapping package="hibernate">     <class name="Classes" table="t_classes">        <id name="id">            <generator class="native"/>        </id>        <property name="name"/>        <set name="students" inverse="true" cascade="all" fetch="subselect">            <key column="classesid"/>            <one-to-many class="Student"/>        </set>     </class> </hibernate-mapping> 测试代码： public class FechTest extends TestCase {     public void testFetch1() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();            Classes classes = (Classes)session.load(Classes.class, 1);            //发出一条sql查询班级            System.out.println("classes.name=" + classes.getName());            //发出一条sql查询这个班级下学生            for (Iterator iter=classes.getStudents().iterator(); iter.hasNext();) {               Student student = (Student)iter.next();               System.out.println("student.name=" + student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }         public void testFetch2() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();            //发出一条查询这三个班级的sql            List classesList = session.createQuery ("select c from Classes c where c.id in(1, 2, 3)").list();            for (Iterator iter=classesList.iterator(); iter.hasNext();) {               Classes classes = (Classes)iter.next();               System.out.println("classes.name=" + classes.getName());               //发出一条查询这三个班级下的所有学生sql               for (Iterator iter1=classes.getStudents().iterator(); iter1.hasNext();) {                   Student student = (Student)iter1.next();                   System.out.println("student.name=" + student.getName());               }            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }       }