1. 什么是hql
HQL是Hibernate Query Language的缩写
2. hql和sql区别/异同
HQL SQL
类名/属性 表名/列名
区分大小写,关键字不区分大小写 不区分大小写
别名 别名
?，从下标0开始计算位置(hibernate5之后不支持) ?，从顺序1开始计算位置
:命名参数 不支持:命名参数
面向对象的查询语言 面向结构查询语言
基本功能演示：
package com.chenjiahao.five.test;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.query.Query;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.chenjiahao.four.entity.Book;
import com.chenjiahao.two.util.SessionFactoryUtils;
public class HqlTest {
private Session session;
private Transaction transaction;
@Before
public void before() {
session = SessionFactoryUtils.openSession();
transaction = session.beginTransaction();
}
@After
public void after() {
transaction.commit();
session.close();
}
/**
* 返回对象（多个）用实体类
*/
@Test
public void testList1() {
Query query = session.createQuery("from Book");
List<Book> list = query.list();
for (Book b : list) {
System.out.println(b);
}
}
/**
* 返回单个列段，用字符串就可以接受
*/
@Test
public void testList2() {
Query query = session.createQuery("select b.bookName as ss from Book b");
List<String> list = query.list();
for (String b : list) {
System.out.println(b);
}
}
/**
* 查两个列段及以上，默认返回的是Object【】
* b.bookId, b.bookName
*/
@Test
public void testList3() {
Query query = session.createQuery("select b.bookId,b.bookName as ss from Book b");
List<Object[]> list = query.list();
for (Object[] b : list) {
System.out.println(Arrays.toString(b));
}
}
/**
* 注意map是函数，所以不区分大小写，返回的是map集合
* new Map(b.bookId as bid, b.bookName as bname)
*/
@Test
public void testList4() {
Query query = session.createQuery("select new mAp(b.bookId,b.bookName) from Book b");
List<Map> list = query.list();
for (Map b : list) {
System.out.println(b);
}
}
/**
* 查两个列段及以上，也可返回对象，前提是有对应的构造函数
* new 构造方法(attr1,attr2)
* new Book(b.bookId, b.price)
*/
@Test
public void testList5() {
Query query = session.createQuery("select new Book(b.bookId,b.bookName) from Book b");
List<Book> list = query.list();
for (Book b : list) {
System.out.println(b);
}
}
/**
* HQL语句支持占位符
* ?占位符
* 从下标0开始计算位置
* hibernate5之后不再支持?占位符（会出现sql攻击）
* sql攻击比如：
* select * from xxx where bid=？
* pst.setString(1,"1 and name="zs"")
*/
@Test
public void testList6() {
// Query query = session.createQuery("from Book where bookId = :bookId");
// query.setParameter("bookId", 1);
// Book b = (Book) query.getSingleResult();
// System.out.println(b);
//:bookIds==:命名参数
//数组
Query query = session.createQuery("from Book where bookId in (:bookIds)");
query.setParameterList("bookIds", new Integer[] {1,2,4});
//集合
// List<Integer> params = new ArrayList<Integer>();
// params.add(1);
// params.add(2);
// params.add(4);
// query.setParameterList("bookIds", params);
List<Book> list = query.list();
for (Book b : list) {
System.out.println(b);
}
}
/**
* HQL支持连接查询
*/
@Test
public void testList7() {
//以前的写法是：select * from t_hibername_order o,t_hibernate_order_item oi where o.order_id=oi.oid
Query query = session.createQuery("select o.orderNo,oi.quantity from Order o,OrderItem oi where o = oi.order");
List<Object[]> list = query.list();
for (Object[] b : list) {
System.out.println(Arrays.toString(b));
}
}
/**
* HQL支持聚合函数
*/
@Test
public void testList8() {
// 还支持sum avg max min
Query query = session.createQuery("select count(*) from Book");
//getSingleResult是用来获取单条记录的
Long singleResult = (Long) query.getSingleResult();
System.out.println(singleResult);
}
/**
* HQL分页
*
* sql：
* sql limit 起始位置，结束
*
* hql:
* 同样的可以自动根据数据库方言生成分页语句
* setFirstResult:设置起始下标
* setMaxResults:设置偏移量
* mysql:hql limit 起始位置，结束
* oracle : select * from (select t.*,rownum rn hql t where t.rn>5)t1 where t1.rn < 10
*
*/
@Test
public void testList9() {
Query query = session.createQuery("from Book");
//设置起始记录下标
query.setFirstResult(2);
// 设置返回的最大结果集
query.setMaxResults(3);
List<Book> list = query.list();
for (Book b : list) {
System.out.println(b);
}
}
}
HQL通用分页查询：
工具类：PageBean(分页的实体类)
package com.chenjiahao.five.util;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;
/**
* 分页工具类
*
*/
public class PageBean {
private int page = 1;// 页码
private int rows = 3;// 页大小
private int total = 0;// 总记录数
private boolean pagination = true;// 是否分页
// 获取前台向后台提交的所有参数
private Map<String, String[]> parameterMap;
// 获取上一次访问后台的url
private String url;
/**
* 初始化pagebean
*
* @param req
*/
public void setRequest(HttpServletRequest req) {
this.setPage(req.getParameter("page"));
this.setRows(req.getParameter("rows"));
// 只有jsp页面上填写pagination=false才是不分页
this.setPagination(!"fasle".equals(req.getParameter("pagination")));
this.setParameterMap(req.getParameterMap());
this.setUrl(req.getRequestURL().toString());
}
public int getMaxPage() {
return this.total % this.rows == 0 ? this.total / this.rows : this.total / this.rows + 1;
}
public int nextPage() {
return this.page < this.getMaxPage() ? this.page + 1 : this.getMaxPage();
}
public int previousPage() {
return this.page > 1 ? this.page - 1 : 1;
}
public PageBean() {
super();
}
public int getPage() {
return page;
}
public void setPage(int page) {
this.page = page;
}
public void setPage(String page) {
this.page = StringUtils.isBlank(page) ? this.page : Integer.valueOf(page);
}
public int getRows() {
return rows;
}
public void setRows(int rows) {
this.rows = rows;
}
public void setRows(String rows) {
this.rows = StringUtils.isBlank(rows) ? this.rows : Integer.valueOf(rows);
}
public int getTotal() {
return total;
}
public void setTotal(int total) {
this.total = total;
}
public void setTotal(String total) {
this.total = Integer.parseInt(total);
}
public boolean isPagination() {
return pagination;
}
public void setPagination(boolean pagination) {
this.pagination = pagination;
}
public Map<String, String[]> getParameterMap() {
return parameterMap;
}
public void setParameterMap(Map<String, String[]> parameterMap) {
this.parameterMap = parameterMap;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
/**
* 获得起始记录的下标
*
* @return
*/
public int getStartIndex() {
return (this.page - 1) * this.rows;
}
@Override
public String toString() {
return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination
+ ", parameterMap=" + parameterMap + ", url=" + url + "]";
}
}
工具类：StringUtils:
package com.chenjiahao.five.util;
public class StringUtils {
// 私有的构造方法，保护此类不能在外部实例化
private StringUtils() {
}
/**
* 如果字符串等于null或去空格后等于""，则返回true，否则返回false
*
* @param s
* @return
*/
public static boolean isBlank(String s) {
boolean b = false;
if (null == s || s.trim().equals("")) {
b = true;
}
return b;
}
/**
* 如果字符串不等于null或去空格后不等于""，则返回true，否则返回false
*
* @param s
* @return
*/
public static boolean isNotBlank(String s) {
return !isBlank(s);
}
}
BaseDao:
package com.chenjiahao.five.util;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.query.Query;
/**
* 1.设置参数问题
* 2.分页代码重复的问题
*
* getCountSql(sql)
* select count(1) from (sql) t
*
* getCountHql(hql)
* hql = " from Book where bookName like :bookName"
* hql ="select * from new Book(bid,bookName) where bookName like :bookName"
*
* @author dell
*
*/
public class BaseDao {
/**
* 同用的参数设值方法
* @param map 参数键值对集合
* @param query 处理hql对象
*/
public void setParam(Map<String, Object> map,Query query) {
if(map !=null && map.size() > 0) {
Object value = null;
Set<Entry<String, Object>> entrySet = map.entrySet();
for (Entry<String, Object> entry : entrySet) {
//有的时候它并不是单纯的字符串，可能是数组比如爱好，也可能是集合
value=entry.getValue();
if (value instanceof Object[]) {
query.setParameterList(entry.getKey(), (Object[])value);
}else if(value instanceof Collection) {
query.setParameterList(entry.getKey(), (Collection)value);
}else {
query.setParameter(entry.getKey(), value);
}
}
}
}
public String getCountHql(String hql) {
// hql = " from Book where bookName like :bookName"
// hql ="select * from new Book(bid,bookName) where bookName like :bookName"
//截取from后面的hql语句
int index = hql.toUpperCase().indexOf("FROM");
return " select count(*) " + hql.substring(index);
}
/**
* 同用查询方法
* @param session
* @param map
* @param hql
* @param pageBean
* @return
*/
public List executeQuery(Session session,Map<String, Object> map,String hql,PageBean pageBean) {
List list=null;
if(pageBean != null && pageBean.isPagination()) {
String countHql = getCountHql(hql);
Query createQuery = session.createQuery(countHql);
this.setParam(map, createQuery);
pageBean.setTotal(createQuery.getSingleResult().toString());
Query query = session.createQuery(hql);
//给预定hql语句执行对象中的参数赋值，有多少赋值多少
this.setParam(map, query);
// 设置分页起始记录下标
query.setFirstResult(pageBean.getStartIndex());
//设置分页返回的最大结果集
query.setMaxResults(pageBean.getRows());
list=query.list() ;
}else {
Query query = session.createQuery(hql);
//给预定hql语句执行对象中的参数赋值，有多少赋值多少
this.setParam(map, query);
list=query.list();
}
return list;
}
}
BookDao：
Bookdao继承Basedao
package com.chenjiahao.four.dao;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.query.Query;
import com.chenjiahao.five.util.BaseDao;
import com.chenjiahao.five.util.PageBean;
import com.chenjiahao.five.util.StringUtils;
import com.chenjiahao.four.entity.Book;
import com.chenjiahao.four.entity.Category;
import com.chenjiahao.two.util.SessionFactoryUtils;
public class BookDao extends BaseDao{
public List<Book> list2(Book book , PageBean pageBean){
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
String bookName = book.getBookName();
Map<String, Object> map=new HashMap<>();
String hql="from Book where 1=1";
if (StringUtils.isNotBlank(bookName)) {
hql += " and bookName like :bookName";
map.put("bookName",bookName);
}
List<Book> list=super.executeQuery(session, map, hql, pageBean);
transaction.commit();
session.close();
return list;
}
}
测试：
@Test
public void testList2() {
Book book=new Book();
PageBean pageBean=new PageBean();
//查询页数
//pageBean.setPage(2);
//不分页
pageBean.setPagination(false);
//查询条件
//book.setBookName("%西%");
List<Book> list = this.bookDao.list2(book, pageBean);
for (Book b : list) {
System.out.println(b);
}
}