Hibernate之HQL

什么是hql？
HQL是Hibernate Query Language的缩写

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

 

处理返回的结果集
单个对象
select没有逗号
Object[]
b.bookId, b.bookName
 Map
new Map(b.bookId as bid, b.bookName as bname)
new 构造方法(attr1,attr2)
new Book(b.bookId, b.price)
单个列段

---

HqlTest：

package com.psy.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.psy.four.entity.Book;
import com.psy.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
     * 
     * 可以自动根据方言生成分页语句
     * setFirstResult：设置起始下标
     * setMaxResults：设置偏移量
     * 
     * 
     */
    @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);
        }
    }
}

hql通用分页查询方法

首先导入两个工具类

package com.psy.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);
    }

}

package com.psy.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 = 2;// 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.psy.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;

import com.psy.two.util.SessionFactoryUtils;

/**
 * 1.设置参数的问题
 * 2.分页代码重复的问题
 * 
 * @author Admin
 * SQL的通用分页的时候
 * getCountSql(sql)
 * select count(1) from(sql) t
 * sql +limit start,offset
 * 
 * getCountHql(hql)
 * hql="from Book where bookName like:bookName"
 * hql="select * from new Book(bid,bookName) where bookName like:bookName"
 * select count(1) hql
 *
 */
public class BaseDao {

    /**
     * 通用的参数设值方法
     * @param map  参数键值对集合
     * @param query  预定义处理的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) {
                //有点时候它并不是单纯的字符串，可能是数组  也可能是集合
                value=entry.getValue();
                if(value instanceof Object []) {
                    query.setParameter(entry.getKey(), (Object [])value);
                }
                else if(value instanceof Collection) {
                    query.setParameter(entry.getKey(), (Collection)value);
                    query.setParameter(entry.getKey(), value);
                }
                else {
                    
                }
            }
        }
        
    }
    
    
    public String getCountHql(String hql) {
//         hql="from Book where bookName like:bookName"
//          hql="select * from new Book(bid,bookName) where bookName like:bookName"
        int index = hql.toUpperCase().indexOf("FROM");
        
     return "select count(*)"+hql.substring( index);
    }
    
    
    /**
     * 通用查询方法
     * @param hql
     * @param session
     * @param map
     * @param pageBean
     * @return
     */
    public List executeQuery(String hql,Session session,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);
            //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);
            List = query.list();
        }
        return null;
        
    }
    
    
    
    
    
    
    
    
}

Dao方法

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(hql, session, map, pageBean);
        
        transaction.commit();
        session.close();
        return list;
    }

}

测试：

@Test
    public void testList2() {
        Book book=new Book();
        PageBean pageBean=new PageBean();
        //pageBean.setPage(2);
        
        List<Book> list=this.bookDao.list1(book, pageBean);
        for (Book b : list) {
            System.out.println(b);
        }
    }