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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

  /**

* 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);

}

}

HibernateUtils.closeSession(session);

}

* 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

      /**

* 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);

}

}

* 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(需要相应对象有相应的构造函数，以次例子为例，需要明白students有以name和id为标准的构造函数)

/**

* 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);

}

}

参见：SimplePropertyQueryTest.java 

*使用别名

/**

* 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);

}

}

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

import java.util.Iterator;

import java.util.List;

import org.hibernate.Session;

import junit.framework.TestCase;

/**

* 实体对象查询

* @author Administrator

*

*/

public class SimpleObjectQueryTest2 extends TestCase {

public void testQuery1() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

/**

* 采用list查询发出一条查询语句，取得Student对象数据、

*

* Hibernate: select student0_.id as id1_, student0_.name as name1_,

* student0_.createTime as createTime1_, student0_.classesid as classesid1_

* from t_student student0_

*

*/

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);

}

}

public void testQuery2() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

/**

* 出现N+1问题

*

* 1：发出查询id列表的sql

*   Hibernate: select student0_.id as col_0_0_ from t_student student0_

*

* N：在依次发出根据id查询Student对象的sql

* Hibernate: select student0_.id as id1_0_, student0_.name as name1_0_,

* student0_.createTime as createTime1_0_, student0_.classesid as classesid1_0_

* from t_student student0_ where student0_.id=?

* 

*/

Iterator iter = session.createQuery("from Student").iterate();

while(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);

}

}

public void testQuery3() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

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

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

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

System.out.println(student.getName());

}

System.out.println("---------------------------------------------");

/**

* 不会出现N+1问题

*

* 因为list操作已经将Student对象放到了一级缓存中，所以再次使用iterate操作的时候

* 它首先发出一条查询id列表的sql，在根据id到缓存中去数据，只有在缓存中找不到相应的

* 数据时，才会发出sql到数据库中查询

*

*/

Iterator iter = session.createQuery("from Student").iterate();

while(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);

}

}

public void testQuery4() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

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

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

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

System.out.println(student.getName());

}

System.out.println("---------------------------------------------");

/**

* 再次发出查询sql

*

* 在默认情况下list每次都会向数据库发出查询对象的sql，除非配置查询缓存，所以下面的list操作

* 虽然在一级缓存中已经有了对象数据，但list默认情况下不会利用缓存，而再次发出sql

*

* 默认情况下，list会向缓存中放入数据，但不会利用数据

*

*/

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);

}

}

}

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

/**

* 条件查询

* @author Administrator

*

*/

public class SimpleConditionQueryTest extends TestCase {

public void testQuery1() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//可以拼字符串

List students = session.createQuery("select s.id, s.name from Student s where s.name like '%1%'").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();

// Query query = session.createQuery("select s.id, s.name from Student s where s.name like ?");

// query.setParameter(0, "%1%");

// List students = query.list();

//可以使用？方式传递参数

//参数的索引从0开始

//传递的参数值，不用单引号引起来

//注意方法链编程

List students = session.createQuery("select s.id, s.name from Student s where s.name like ?")

.setParameter(0, "%1%")

.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();

//使用 ：参数名称 的方式传递参数值

List students = session.createQuery("select s.id, s.name from Student s where s.name like :myname")

      .setParameter("myname", "%1%")

      .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 testQuery4() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//使用 ：参数名称 的方式传递参数值

List students = session.createQuery("select s.id, s.name from Student s where s.name like :myname and s.id=:myid")

.setParameter("myname", "%1%")

.setParameter("myid", 12)

.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 testQuery5() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//支持in，需要使用setParameterList进行参数传递

List students = session.createQuery("select s.id, s.name from Student s where s.id in(:myids)")

.setParameterList("myids", new Object[]{1, 2, 3, 4, 5})

.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 testQuery6() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//查询2008年2月创建的学生

List students = session.createQuery("select s.id, s.name from Student s where date_format(s.createTime, '%Y-%m')=?")

.setParameter(0, "2008-02")

.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 testQuery7() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

//查询2008-01-10到2008-02-15创建的学生

List students = session.createQuery("select s.id, s.name from Student s where s.createTime between ? and ?")

.setParameter(0, sdf.parse("2008-01-10 00:00:00"))

.setParameter(1, sdf.parse("2008-02-15 23:59:59"))

.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);

}

}

}

4、hibernate也支持直接使用sql进行查询

参见：SqlQueryTest.java

session = HibernateUtils.getSession();

session.beginTransaction();

List students = session.createSQLQuery("select * from t_student").list();

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

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

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

}

session.getTransaction().commit();

5、外置命名查询

* 在映射文件中采用 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

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);

}

}

}

SELECT s FROM Student s where s.id

]]>

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

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

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

SELECT s FROM Student s where s.id

]]>

/**

* 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);

}

}

}

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

/**

* 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);

}

}

}

8、对象导航查询，在hql中采用 . 进行导航【重要】

参见：ObjectNavQueryTest.java

/**

* 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);

}

}

}

9、连接查询【重要】

* 内连

* 外连接（左连接/右连接）

参见：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);

}

}

}

10、统计查询【重要】

参见：StatQueryTest.java

package com.bjsxt.hibernate;

import java.util.Iterator;

import java.util.List;

import org.hibernate.Session;

import junit.framework.TestCase;

/**

* 统计查询

* @author Administrator

*

*/

public class StatQueryTest extends TestCase {

public void testQuery1() {

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

// List students =session.createQuery("select count(*) from Student").list();

// Long count = (Long)students.get(0);

// System.out.println(count);

Long count = (Long)session.createQuery("select count(*) from Student").uniqueResult();

System.out.println(count);

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, count(s) from Student s join s.classes c " +

"group by c.name order by c.name").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);

}

}

}

11、DML风格的操作（尽量少用，因为和缓存不同步）

参见：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);

}

}

}

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