什么是hql?

     HQL是Hibernate Query Language的缩写

hql和sql区别/异同:

HQLSQL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：

     1 、单个对象      2、 Object[]      3、 Map      4 、new 构造方法(attr1,attr2)

/** * 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中使用占位符：

1 、?占位符 （从下标0开始计算位置，hibernate5之后不再支持?占位符） 2 、命名参数

/** * 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); } }

连接查询:

/** * 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)); } }

聚合函数

/** * HQL支持聚合函数 */ @Test public void testList8() { Query query = session.createQuery("select count(*) from Book"); //singleResult是用来获取单条记录的 Long singleResult = (Long) query.getSingleResult(); System.out.println(singleResult); }

hql分页

/** * HQL分页 * 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:

分页工具类PageBean:

package com.liyi.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.liyi.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

package com.liyi.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.liyi.five.util.BaseDao; import com.liyi.five.util.PageBean; import com.liyi.five.util.StringUtils; import com.liyi.four.entity.Book; import com.liyi.two.util.SessionFactoryUtils; public class BookDao extends BaseDao{ public List<Book> list2(Book book, PageBean pageBean) { Session session = SessionFactoryUtils.openSession(); Transaction transaction = session.beginTransaction(); Map<String, Object> map = new HashMap<>(); String hql = "from Book where 1 = 1"; if (StringUtils.isNotBlank(book.getBookName())) { hql += " and bookName like :bookName"; map.put("bookName", book.getBookName()); } List<Book> list = super.executeQuery(session, map, hql, pageBean); transaction.commit(); session.close(); return list; } }

BaseDao

package com.liyi.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 * 2、分页代码重复的问题 * @author 224李毅 * */ 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) { //有时候它并不是单纯的字符串，而是数组，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) { int index = hql.toUpperCase().indexOf("FROM"); return "select count(*) "+ hql.substring(index); } 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 list; } }

BookDaoTest

package com.liyi.four.dao; import java.util.List; import org.junit.Test; import com.liyi.five.util.PageBean; import com.liyi.four.entity.Book; public class BookDaoTest { private BookDao bookDao = new BookDao(); @Test public void testList2() { Book book = new Book(); PageBean pageBean = new PageBean(); // pageBean.setPage(2); // book.setBookName("%三国演义%"); pageBean.setPagination(false); List<Book> list = this.bookDao.list2(book, pageBean); for (Book book2 : list) { System.out.println(book2); } } }

效果：