Hibernate学习44 -- 抓取策略4 -- 批量抓取（Batch fetching）

batch-size属性，可以批量加载实体类或集合，例如：，数字“3”表示每次合并几条sql。

例子代码如下：

Student.hbm.xml <hibernate-mapping package="hibernate">     <class name="Classes" table="t_classes" batch-size="3">        <id name="id">            <generator class="native"/>        id>        <property name="name"/>        <set name="students" inverse="true" cascade="all">            <key column="classesid"/>            <one-to-many class="Student"/>        set>     class> hibernate-mapping> 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" batch-size="5">            <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();                       List students = session.createQuery ("select s from Student s where s.id in(:ids)")           .setParameterList("ids", new Object[]{1, 11, 21, 31, 41, 51, 61, 71, 81, 91})           .list();            for (Iterator iter=students.iterator(); iter.hasNext();) {               Student  student = (Student)iter.next();               System.out.println("student.name=" + student.getName());               System.out.println("classes.name=" + student.getClasses().getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }     public void testFetch1() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       List classesList = session.createQuery ("select c from Classes c").list();            for (Iterator iter=classesList.iterator(); iter.hasNext();) {               Classes classes = (Classes)iter.next();               System.out.println("classes.name=" + classes.getName());               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);        }          } }