Hibernate学习42 -- 抓取策略2 -- 查询抓取

fetch="select",另外发送一条select语句抓取当前对象关联实体或集合。例如：<many-to-one name="classes" column="classesid" fetch="select"/>

例子代码如下：

Student.hbm.xml <hibernate-mapping>     <class name="hibernate.Student" table="t_student">             <id name="id">            <generator class="native"/>        </id>        <property name="name"/>        <many-to-one name="classes" column="classesid" fetch="select"/>     </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" fetch="select">            <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();                       Student student = (Student)session.load(Student.class, 1);            //发出一条sql查询学生            System.out.println("student.name=" + student.getName());            //发出一条sql查询班级            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 testFetch2() {        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);        }     }   }