什么是HQL？
HQL是Hibernate Query Language的缩写，提供更加丰富灵活、更为强大的查询能力；HQL更接近SQL语句查询语法。
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
HqlTest
package com.wangshaoyang.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.wangshaoyang.four.entity.Book;
import com.wangshaoyang.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）
*/
@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【】
*/
@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
*/
@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
*/
@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
*/
@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);
Query query = session.createQuery("from Book where bookId in (:bookIds)");
query.setParameterList("bookIds", new Integer[] {1,2,4});
// 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() {
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() {
Query query = session.createQuery("select count(*) from Book");
Long singleResult = (Long) query.getSingleResult();
System.out.println(singleResult);
}
/**
* HQL分页
*/
@Test
public void testList9() {
Query query = session.createQuery("from Book");
query.setFirstResult(2);
query.setMaxResults(3);
List<Book> list = query.list();
for (Book b : list) {
System.out.println(b);
}
}
}
我们先导入工具类 StringUtils
package com.wangshaoyang.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);
}
}
PageBean
package com.wangshaoyang.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 + "]";
}
}
BaseDao
package com.wangshaoyang.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、设置参数的问题
* 2、分页代码重复的问题
*
* sql的通用分页的时候
*
* getCountSql(sql)
* sql+ limit start,offset
* select count(1) from (sql) t
*
* getCountHql(hql)
* hql="from new Book(bid,bookName) where bookName like :bookName" 如果是这样就会报错
* hql =select count(1) hql
*
* @author
*
*/
public class BaseDao {
/**
*设置参数的方法
* @param map
* @param query
*/
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) {
//例子中的圣墟，但是有点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);
}
}
}
}
/**
* 拼接HQL语句
* @param hql
* @return
*/
public String getCountHql(String hql) {
int index = hql.toUpperCase().indexOf("FROM");
return "select count(*)"+hql.substring(index);
}
/**
* 通用查询的方法
* @param session
* @param hql
* @param map
* @param pageBean
* @return
*/
public List executeQuery(Session session,String hql,Map<String, Object> map,PageBean pageBean) {
List list=null;
if(pageBean != null && pageBean.isPagination()) {
String countHql=getCountHql(hql);
Query countQuery = session.createQuery(countHql);
this.setParam(map, countQuery);
pageBean.setTotal(countQuery.getSingleResult().toString());
Query query = session.createQuery(hql);
// 给预定义hql语句执行对象中的参数赋值，有多少赋值多少
this.setParam(map, query);
query.setFirstResult(pageBean.getStartIndex());
query.setMaxResults(pageBean.getRows());
list = query.list();
}else {
Query query = session.createQuery(hql);
this.setParam(map, query);
list = query.list();
}
return list;
}
}
然后写一个BookDao并继承BaseDao
package com.wangshaoyang.five.dao;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.query.Query;
import com.wangshaoyang.five.util.BaseDao;
import com.wangshaoyang.five.util.PageBean;
import com.wangshaoyang.five.util.StringUtils;
import com.wangshaoyang.four.entity.Book;
import com.wangshaoyang.two.util.SessionFactoryUtils;
public class BookDao extends BaseDao{
/**
* 需求:
* 写一个带查询条件的并且能分页的方法
* @param book
* @param pageBean
* @return
*/
public List<Book> list1(Book book,PageBean pageBean) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
String bookName=book.getBookName();
String hql="from Book where 1=1";
if(StringUtils.isNotBlank(bookName)) {
hql+=" and bookName like :bookName";
}
Query query = session.createQuery(hql);
// query相当于sql所用的prepareStatement
if(StringUtils.isNotBlank(bookName)){
query.setParameter("bookName","%"+bookName+"%");
}
// 通过写上述代码会发现，同样的if判断写了两次
// 下面这个代码每个实体类分页代码都得写
if(pageBean!=null && pageBean.isPagination()) {
query.setFirstResult(pageBean.getStartIndex());
query.setMaxResults(pageBean.getRows());
}
List<Book> list = query.list();
transaction.commit();
session.close();
return list;
}
/**
* 需求:
* 写一个带查询条件的并且能分页的方法
* @param book
* @param pageBean
* @return
*/
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, hql, map, pageBean);
transaction.commit();
session.close();
return list;
}
}
package com.wangshaoyang.four.dao;
import java.util.List;
import org.junit.Test;
import com.wangshaoyang.five.util.PageBean;
import com.wangshaoyang.four.entity.Book;
import com.wangshaoyang.four.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
@Test
public void test1List1() {
Book book=new Book();
PageBean pageBean=new PageBean();
// pageBean.setPage(2);
book.setBookName("嘻嘻");
List<Book> list = bookDao.list1(book, pageBean);
for (Book b : list) {
System.out.println(b);
}
}
@Test
public void test1List2() {
Book book=new Book();
PageBean pageBean=new PageBean();
pageBean.setPage(2);
// book.setBookName("斗气");
pageBean.setPagination(false);
List<Book> list = bookDao.list2(book, pageBean);
for (Book b : list) {
System.out.println(b);
}
}
}
运行 public void test1List2() 就可以得到
今天就更新到这里
喜欢的可以关注我
我会不定时更新的哦
