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

测试类

package com.tt.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.tt.four.entity.Book;
import com.tt.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
	 * 
	 * sql
	 * sql limit 5,5
	 * 同样的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);
		}
	}
}

小结

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

聚合函数（这个和sql差不多）

sum
avg
max
min
count

hql分页

int page = 2;// 页码：page
int row = 10;// 每页行数：rows
query.setFirstResult((page - 1) * row);// 设置起始记录下标
query.setMaxResults(row);// 设置返回的最大结果集

通用分页方法

BaseDao.java

package com.tt.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) 
 *  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"
 *   select count(1) hql 
 *   
 * @author tt
 *
 */
public class BaseDao {
	/**
	 * 通过的参数设值的方法	
	 * @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) {
				//列子的西游记，但是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) {
		//= "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 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 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语句执行对象的参数赋值，有多少赋值多少
			this.setParam(map, query);
			list = query.list();
		}
		return list;
	}
}

PageBean.java

package com.tt.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 + "]";
	}

}

StringUtils.java

package com.tt.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);
	}

}

BookDao.java

package com.tt.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.tt.five.util.BaseDao;
import com.tt.five.util.PageBean;
import com.tt.five.util.StringUtils;
import com.tt.four.entity.Book;
import com.tt.four.entity.Category;
import com.tt.two.util.SessionFactoryUtils;

public class BookDao extends BaseDao{
	public Integer addBook(Book book) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Integer bid = (Integer) session.save(book);
		transaction.commit();
		session.close();
		return bid;
	}
	
	public Integer addCategory(Category category) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Integer cid = (Integer) session.save(category);
		transaction.commit();
		session.close();
		return cid;
	}
	
	public Category getCategory(Category category) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Category c = session.get(Category.class, category.getCategoryId());
		transaction.commit();
		session.close();
		return c;
	}
	
	public Book getBook(Book book) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Book b = session.get(Book.class, book.getBookId());
		if (b != null && new Integer(1).equals(book.getInitCategories())) {
			Hibernate.initialize(b.getCategories());
		}
		transaction.commit();
		session.close();
		return b;
	}
	
	public void delBook(Book book) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		session.delete(book);
		transaction.commit();
		session.close();
	}
	
	public void delCategory(Category category) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Category c = session.get(Category.class, category.getCategoryId());
		if(c!=null) {
			for (Book b : c.getBooks()) {
//				通过在被控方通过主控方来解除关联关系，最后被控方再做删除
				b.getCategories().remove(c);
			}
		}
		session.delete(c);
		transaction.commit();
		session.close();
	}
	/**
	 * 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相当于前面sql所用的prepareStatement
		Query query = session.createQuery(hql);
		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;
	}
	
	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;
	}
}

BookDaoTest.java(测试方法)

@Test
	public void testList2() {
		Book book = new Book();
		PageBean pageBean = new PageBean();
//		pageBean.setPage(2);
//		book.setBookName("%的%");
		List<Book> list = this.bookDao.list2(book, pageBean);
		for (Book b : list) {
			System.out.println(b);
		}
	}

效果图：