hql简单属性查询

 

 

1、简单属性查询【重要】

       * 单一属性查询，返回结果集属性列表，元素类型和实体类中相应的属性类型一致

       * 多个属性查询,返回的集合元素是对象数组,数组元素的类型和对应的属性在实体类中的类型一致

         数组的长度取决与select中属性的个数

       * 如果认为返回数组不够对象化，可以采用hql动态实例化Student对象

       参见：SimplePropertyQueryTest.java 

/**

 * 简单属性查询

 * @author Administrator

 *

 */

public class SimplePropertyQueryTest extends TestCase {

   

    /**

     * 单一属性查询

     */

    public void testQuery1() {

       Session session = null;

       try {

           session = HibernateUtils.getSession();

           session.beginTransaction();

          

           //返回结果集属性列表，元素类型和实体类中相应的属性类型一致

           List students = session.createQuery("select name from Student").list();

           for (Iterator iter=students.iterator(); iter.hasNext();) {

              String name = (String)iter.next();

              System.out.println(name);

           }

           session.getTransaction().commit();

       }catch(Exception e) {

           e.printStackTrace();

           session.getTransaction().rollback();

       }finally {

           HibernateUtils.closeSession(session);

       }

    }

 

    /**

     * 多个属性查询

     */

    public void testQuery2() {

       Session session = null;

       try {

           session = HibernateUtils.getSession();

           session.beginTransaction();

          

           //查询多个属性，其集合元素是对象数组

           //数组元素的类型和对应的属性在实体类中的类型一致

           //数组的长度取决与select中属性的个数

           List students = session.createQuery("select id, name from Student").list();

           for (Iterator iter=students.iterator(); iter.hasNext();) {

              Object[] obj = (Object[])iter.next();

              System.out.println(obj[0] + "," + obj[1]);

           }

           session.getTransaction().commit();

       }catch(Exception e) {

           e.printStackTrace();

           session.getTransaction().rollback();

       }finally {

           HibernateUtils.closeSession(session);

       }

    }

 

    /**

     * 返回Student实体对象

     */

    public void testQuery3() {

       Session session = null;

       try {

           session = HibernateUtils.getSession();

           session.beginTransaction();

          

           //如果认为返回数组不够对象化，可以采用hql动态实例化Student对象

           //此时list中为Student对象集合

           List students = session.createQuery("select new Student(id, name) from Student").list();

           for (Iterator iter=students.iterator(); iter.hasNext();) {

              Student student = (Student)iter.next();

              System.out.println(student.getId() + "," + student.getName());

           }

           session.getTransaction().commit();

       }catch(Exception e) {

           e.printStackTrace();

           session.getTransaction().rollback();

       }finally {

           HibernateUtils.closeSession(session);

       }

    }

 

    /**

     * 使用别名

     */

    public void testQuery4() {

       Session session = null;

       try {

           session = HibernateUtils.getSession();

           session.beginTransaction();

          

           //可以使用别名

           List students = session.createQuery("select s.id, s.name from Student s").list();

           for (Iterator iter=students.iterator(); iter.hasNext();) {

              Object[] obj = (Object[])iter.next();

              System.out.println(obj[0] + "," + obj[1]);

           }

           session.getTransaction().commit();

       }catch(Exception e) {

           e.printStackTrace();

           session.getTransaction().rollback();

       }finally {

           HibernateUtils.closeSession(session);

       }

    }