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); } } }