hibernate实例简析-hibernate_hql（三）

最新推荐文章于 2019-09-04 02:13:48 发布

iteye_20137

最新推荐文章于 2019-09-04 02:13:48 发布

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分类专栏： hibernate 文章标签： Hibernate C C++ C# J#

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本文介绍了Hibernate中的HQL查询技术，包括对象导航查询、外置命名查询和连接查询等核心内容。通过具体示例展示了如何使用HQL进行复杂的数据检索。

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1、对象导航查询，在hql中采用 . 进行导航【重要】
参见：ObjectNavQueryTest.java

List students = session.createQuery("select s.name from Student s where s.classes.name like '%1%'").list();
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    String name = (String)iter.next();
    System.out.println(name);
   }

2、外置命名查询
* 在映射文件中采用<query>标签来定义hql
* 在程序中采用session.getNamedQuery()方法得到hql查询串
参见：Student.hbm.xml、NameQueryTest.java

List students = session.getNamedQuery("searchStudents")
        .setParameter(0, 10)
        .list();
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Student student = (Student)iter.next();
    System.out.println(student.getName());
   }

<hibernate-mapping>
<class name="com.bjsxt.hibernate.Student" table="t_student">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="name"/>
  <property name="createTime"/>
  <many-to-one name="classes" column="classesid"/>
  <filter name="filtertest" condition="id < :myid"/>
</class>

<query name="searchStudents">
  <![CDATA[
   SELECT s FROM Student s where s.id<?
  ]]>
</query>

<filter-def name="filtertest">
  <filter-param name="myid" type="integer"/>
</filter-def>
</hibernate-mapping>

3、连接查询【重要】
* 内连
* 外连接（左连接/右连接）
参见：JoinQueryTest.java

List students = session.createQuery("select c.name, s.name from Student s inner join s.classes c").list();
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Object[] obj = (Object[])iter.next();
    System.out.println(obj[0] + "," + obj[1]);
   }

===

List students = session.createQuery("select c.name, s.name from Classes c left join c.students s").list();
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Object[] obj = (Object[])iter.next();
    System.out.println(obj[0] + "," + obj[1]);
   }

===

List students = session.createQuery("select c.name, s.name from Classes c right join c.students s").list();
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Object[] obj = (Object[])iter.next();
    System.out.println(obj[0] + "," + obj[1]);
   }

4、

for(int i=0; i<10; i++){

     Classes classes = new Classes();
     classes.setName("班级"+i);
     session.save(classes);

     for(int j=0; j<10; j++){
      Student student = new Student();
      student.setName("班级"+i+"的学生"+j);
      student.setCreateTime(randomDate("2008-01-01","2008-03-01"));

      //在内存中建立由student指向classes的引用
      student.setClasses(classes);
      session.save(student);
     }
    }

    for(int i=0; i<5; i++){
     Classes classes = new Classes();
     classes.setName("无学生班级"+i);
     session.save(classes);
    }

    for(int i=0; i<10; i++){
     Student student = new Student();
     student.setName("无业游民"+i);
     session.save(student);
    }