Hibernate之HQL

Posted 2022-04-23 chenjiahao9527

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);