4.hql查询实体:测试

package com.bjpowernode.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("2009-07-01","2009-09-01"));

//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;
}
}

package com.bjpowernode.hibernate;

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 SimpleObjectQueryTest1 extends TestCase {

@SuppressWarnings("unchecked")
public void testQuery1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
//返回Student对象的集合
//可以忽select关键字
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);
}
}

@SuppressWarnings("unchecked")
public void testQuery2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
//返回Student对象的集合
//可以忽select关键字，可以加入别名
List students = session.createQuery("from Student s").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);
}
}

@SuppressWarnings("unchecked")
public void testQuery3() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
//返回Student对象的集合
//可以忽select关键字，可以采用as命名别名
List students = session.createQuery("from Student as s").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);
}
}

@SuppressWarnings("unchecked")
public void testQuery4() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
//返回Student对象的集合
//如果使用select查询实体对象，必须使用别名
List students = session.createQuery("select s from Student s").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);
}
}

@SuppressWarnings("unchecked")
public void testQuery5() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
//不支持select * from .....,这种语法
List students = session.createQuery("select * from Student s").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);
}
}

}

package com.bjpowernode.hibernate;

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 {

@SuppressWarnings("unchecked")
public void testQuery1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
/**
* 采用list查询实体对象会发出一条查询语句，取得实体对象数据
*
* Hibernate: select student0_.id as id0_, student0_.name as name0_,
* student0_.createTime as createTime0_, student0_.classesid as classesid0_
* 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);
}
}

@SuppressWarnings("unchecked")
public void testQuery2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
/**
* 会出现N+1问题，所谓的N+1指的是发出了N+1条sql语句
*
* 1:发出一条查询id列表的语句
* Hibernate: select student0_.id as col_0_0_ from t_student student0_
*
* N:根据id发出N条sql语句，加载相关的对象
* Hibernate: select student0_.id as id0_0_, student0_.name as name0_0_,
* student0_.createTime as createTime0_0_, student0_.classesid as classesid0_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);
}
}

@SuppressWarnings("unchecked")
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("-----------------------------------------------------");
/**
* 避免了N+1问题
*
* 因为执行list操作后会将数据放到session的缓存中（一级缓存），所以采用iterate的时候
* 首先会发出一条查询id列表的语句，再根据id到缓存中加载相应的数据，如果缓存中存在与之匹配的数据
* 则不再发出根据id查询的sql语句，直接使用缓存中的数据
*
* Iterate方法如果缓存中存在数据，它可以提高性能，否则出现N+1问题
*
*/
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);
}
}

@SuppressWarnings("unchecked")
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("-----------------------------------------------------");

/**
* 再此发出查询语句
*
* 在默认情况下，每次执行list查询实体对象都会发出查询语句，除非配置了查询缓存
* 虽然一级缓存中存在Student数据，但list不用，所以仍然发出查询语句，
*
* 其实list就是只向缓存中放入数据，而不利用缓存中的数据
*/
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);
}
}
}