hibernate查询语言hql

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dzliyanbing 2009-03-09 11:34:41 ©著作权

文章标签 职场 Hibernate 休闲 hibernate查询语言hql 文章分类 Java 后端开发

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在hql中关键字不区分大小写，但是属性和类名区分大小写

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

2、实体对象查询【重要】
    * N + 1问题，在默认情况下，使用query.iterate查询，有可以能出现N+1问题
    所谓的N+1是在查询的时候发出了N+1条sql语句
    1: 首先发出一条查询对象id列表的sql
    N: 根据id列表到缓存中查询，如果缓存中不存在与之匹配的数据，那么会根据id发出相应的sql语句
    * list和iterate的区别？
        * list每次都会发出sql语句，list会向缓存中放入数据，而不利用缓存中的数据
        * iterate：在默认情况下iterate利用缓存数据，但如果缓存中不存在数据有可以能出现N+1问题
    参见：SimpleObjectQueryTest1.java/SimpleObjectQueryTest2.java

3、条件查询【重要】
    * 可以采用拼字符串的方式传递参数
    * 可以采用？来传递参数（索引从0开始）
    * 可以采用 :参数名来传递参数
    * 如果传递多个参数，可以采用setParamterList方法
    * 在hql中可以使用数据库的函数，如：date_format
    参见：SimpleConditionQueryTest.java

4、hibernate也支持直接使用sql进行查询
    参见：SqlQueryTest.java

5、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

6、查询过滤器
    * 在映射文件中定义过滤器参数
    * 在类的映射中使用这些参数
    * 在程序中启用过滤器
    参见：Student.hbm.xml、FilterQueryTest.java

7、分页查询【重要】
    * setFirstResult()，从0开始
    * setMaxResults,每页显示多少条数据
    参见：PageQueryTest.java

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

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

10、统计查询【重要】
    参见：StatQueryTest.java

11、DML风格的操作（尽量少用，因为和缓存不同步）
    参见：DMLQueryTest.java

Classes.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "[url]http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd[/url]">
<hibernate-mapping package="com.bjsxt.hibernate">
    <class name="Classes" table="t_classes">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <set name="students" inverse="true" cascade="all">
            <key column="classesid"/>
            <one-to-many class="Student"/>
        </set>
    </class>
</hibernate-mapping>

Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "[url]http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd[/url]">
<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>

Classes.java
package com.bjsxt.hibernate;

import java.util.Set;

public class Classes {

    private int id;

    private String name;

    private Set students;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set getStudents() {
        return students;
    }

    public void setStudents(Set students) {
        this.students = students;
    }

}

Student.java
package com.bjsxt.hibernate;

import java.util.Date;

public class Student {

    private int id;

    private String name;

    private Date createTime;

    private Classes classes;

    public Student() {}

    public Student(int id, String name) {
        this.id = id;
        this.name = name;
    }


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Classes getClasses() {
        return classes;
    }

    public void setClasses(Classes classes) {
        this.classes = classes;
    }

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
}

DMLQueryTest.java
package com.bjsxt.hibernate;

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* DML风格的操作
* @author Administrator
*
*/
public class DMLQueryTest extends TestCase {

    public void testQuery1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            session.createQuery("update Student s set s.name=? where s.id < ?")
                    .setParameter(0, "李四")
                    .setParameter(1, 5)
                    .executeUpdate();

            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
}

FilterQueryTest.java
package com.bjsxt.hibernate;

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

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* 查询过滤器
* @author Administrator
*
*/
public class FilterQueryTest extends TestCase {

    public void testQuery1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            session.enableFilter("filtertest")
                    .setParameter("myid", 10);

            List students = session.createQuery("from Student").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println(student.getName());
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
}

InitData.java
package com.bjsxt.hibernate;

import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;

public class InitData {

public static void main(String[] args) {
Session session = HibernateUtils.getSession();

try {
session.beginTransaction();

                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);
                }

                session.getTransaction().commit();
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            } finally{
                HibernateUtils.closeSession(session);
            }
        }

        /**
        * 获取随机日期
        * @param beginDate 起始日期，格式为：yyyy-MM-dd
        * @param endDate 结束日期，格式为：yyyy-MM-dd
        * @return
        */
        private static Date randomDate(String beginDate,String endDate){
            try {
                SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
                Date start = format.parse(beginDate);
                Date end = format.parse(endDate);

                if(start.getTime() >= end.getTime()){
                    return null;
                }

                long date = random(start.getTime(),end.getTime());

                return new Date(date);
            } catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        }

        private static long random(long begin,long end){
            long rtn = begin + (long)(Math.random() * (end - begin));
            if(rtn == begin || rtn == end){
                return random(begin,end);
            }
            return rtn;
        }
}

JoinQueryTest.java
package com.bjsxt.hibernate;

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

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* 连接查询
* @author Administrator
*
*/
public class JoinQueryTest extends TestCase {

    public void testQuery1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            //List students = session.createQuery("select c.name, s.name from Student s join s.classes c").list();
            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]);
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }

    public void testQuery2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            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]);
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }

    public void testQuery3() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            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]);
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }

}

NameQueryTest.java
package com.bjsxt.hibernate;

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

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* 外置命名查询
* @author Administrator
*
*/
public class NameQueryTest extends TestCase {

    public void testQuery1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            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());
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
}

ObjectNavQueryTest.java
package com.bjsxt.hibernate;

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

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* 对象导航查询
* @author Administrator
*
*/
public class ObjectNavQueryTest extends TestCase {

    public void testQuery1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            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);
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
}

PageQueryTest.java
package com.bjsxt.hibernate;

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

import org.hibernate.Session;

import junit.framework.TestCase;

/**
* 分页查询
* @author Administrator
*
*/
public class PageQueryTest extends TestCase {

    public void testQuery1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();

            List students = session.createQuery("from Student")
                                    .setFirstResult(1)
                                    .setMaxResults(2)
                                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println(student.getName());
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
}