HIbernate查询
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<query>标签来定义hql</query>
* 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);
}
}
}
<query name="searchStudents"></query>
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
<?xml version="1.0"?>
/p>
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping></hibernate-mapping>
<class name="com.bjsxt.hibernate.Student" table="t_student"></class>
<id name="id"></id>
<generator class="native"></generator>
<property name="name"></property>
<property name="createTime"></property>
<many-to-one name="classes" column="classesid"></many-to-one>
<filter name="filtertest" condition="id < :myid"></filter>
<query name="searchStudents"></query>
SELECT s FROM Student s where s.id
]]>
<filter-def name="filtertest"></filter-def>
<filter-param name="myid" type="integer"></filter-param>
/**
* 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);
}
}
}