1.数据库已经建立视图，hibernate只是把视图当作普通的表来映射。

视图VIEW_MER_INST_POS:

select MER.DAYS_MERCHT_ID MER_ID,

       INST.DAYS_MERCHT_ID INST_ID,

       POS.POS_ID POS_ID

from tbl_days_mercht_attr MER,

     tbl_days_mercht_info INST,

     tbl_days_mercht_pos_info POS

where MER.days_mercht_id = INST.up_days_mercht_id

and INST.days_mercht_id = POS.days_mercht_id

hbm.xml配置

<class

    name="db.po.ViewMerInstPos"

    table="VIEW_MER_INST_POS"

>

    <composite-id>

            <key-property

            name="merId"

            column="MER_ID"

            type="java.lang.String"

            length="8"

        />

        <key-property

            name="instId"

            column="INST_ID"

            type="java.lang.String"

            length="8"

        />

        <key-property

            name="posId"

            column="POS_ID"

            type="java.lang.String"

            length="8"

        />

</class>

</hibernate-mapping>

2.数据库没有视图，用hibernate自己做视图映射

   hibernate还允许把只读的实体映射到一个数据库的子查询中。当你想用视图代替一张基本表的时候，这是有用的。

2.1运用标签

    <subselect> </subselect>

2.2 举例

    数据库存在学生基本信息表，现在想建立一个视图来统计每个年龄段的学生人数，并用一个实体类的进行映射。

 

（1）学生信息表的的映射文件(Student.hbm.xml)如下：

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC

 "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

 "">

<hibernate-mapping package="com.zds.domain">

    <class name="Student" table="student" >

        <id name="id" column="student_id">

            <generator class="native"/> 

        </id>

        <property name="name"/>

        <property name="age"/>

        <property name="birthday"/>

        <property name="grade"/>

    </class>

</hibernate-mapping> 

(2)学生统计信息配置文件(StudentStatic.hbm.xml)如下：

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC

 "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

 "">

<hibernate-mapping package="com.zds.domain">

    <class  name="StudentStatic" entity-name="studentStatic">    

   <subselect>

      select count(student.student_id) as student_num, student.age as student_age

      from student as student

      group by age   

     </subselect>

     <synchronize table="student"/>      

     <composite-id>

            <key-property name="age" column="student_age" type="int" /> 

     </composite-id>

     <property name="student_num" column="student_num" type="int"/>

    </class>

</hibernate-mapping>

【其中synchronize表示当表的数据发生变化的时候，视图的数据也会发生变化。】

(3)学生统计信息实体类(StudentStatic.java)定义如下：

package com.zds.domain;

import java.io.Serializable;

public class StudentStatic implements Serializable{

 private int age;

 private int student_num;

 

 public int getStudent_num() {

  return student_num;

 }

 public void setStudent_num(int student_num) {

  this.student_num = student_num;

 }

 public int getAge() {

  return age;

 }

 public void setAge(int age) {

  this.age = age;

 }

 

}

现在查询视图，打印出学生统计信息：

List<StudentStatic> studentStaticData = new ArrayList<StudentStatic>();

  Session session = null;

  Transaction tx = null;

  session = HibernateUtil.getSession();

  tx = session.beginTransaction();

  Query query = session.createQuery("from studentStatic");

  studentStaticData = (List<StudentStatic>) query.list();

  tx.commit();

  for(StudentStatic studentStatic:studentStaticData)

  {

      System.out.println("年龄：  "+studentStatic.getAge()+"  

       人数："+studentStatic.getStudent_num());

  }