Hibernate HQL 查询简单属性-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_4399/article/details/81788820

本文介绍使用Hibernate进行不同类型的属性查询方法，包括单一属性查询、多个属性查询、返回实体对象及使用别名等技巧。通过具体代码示例展示了如何利用HQL进行高效的数据检索。

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import java.util.Iterator;
import java.util.List;

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* 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);
        }
    }

    /**
    * 使用别名
    */
    public void testQuery5() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            //可以使用as命名别名
            List students = session.createQuery("select s.id, s.name from Student as 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);
        }
    }

}