一、HQL
1、 什么是hql HQL是Hibernate Query Language的缩写
2、hql和sql的区别：
1、首先，hql是面向对象查询的；sql是面向数据库做查询。 2、hql的语法结构：from + 类名+类对象 +where+类对象属性的条件； sql的语法结构：from +数据库表名+ where +表字段条件 3、新增：hql不需要再用insert语句，只需构造新增对象后调用save()方法 4、修改：hql不需要再用update语句，只需得到修改对象后调用update()方法 5、删除：hql不需要再用delete语句，只需得到要删除的对象后调用delete()方法 注：hql区分大小写,关键字不区分大小写3、测试查询：
package com.yj.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.yj.four.entity.Book; import com.yj.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 * 自动跟据方言生成分页语句 * setFirstResult：设置起始下标 * setMaxResults：设置偏移量（每页多少条数据） */ @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); } } }二：分页查询： 工具类： 判断是否为空：
package com.yj.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); } }分页：
package com.yj.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 + "]"; } }为了方便，把公用代码放在一个baseDao里面 baseDao
package com.yj.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 * * @author 雷神 * */ public class BaseDao { /** * 通用的参数设置方法 * @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) { //例子的圣墟，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) { //hql = "from Book where bookName like :bookName" // hql = " select * from new Book where(bid,bookName) where bookName like :bookName" 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 createQuery = session.createQuery(countHql); this.setParam(map, createQuery); pageBean.setTotal(createQuery.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; } }下面测试写了一个用了baseDao和没用baseDao的两个测试： dao方法：
package com.yj.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.yj.five.util.BaseDao; import com.yj.five.util.PageBean; import com.yj.five.util.StringUtils; import com.yj.four.entity.Book; import com.yj.four.entity.Category; import com.yj.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相当于以前学过的prepareStatement Query query = session.createQuery(hql); if(StringUtils.isNotBlank(bookName)) { query.setParameter("bookName", bookName); } //通过上述代码，可以发现同样的if判断写了两次 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; } }测试类：
package com.yj.four.dao; import java.util.List; import org.junit.Test; import com.yj.five.util.PageBean; import com.yj.four.entity.Book; import com.yj.four.entity.Category; public class BookDaoTest { private BookDao bookDao = new BookDao(); @Test public void testGetBook() { Book book = new Book(); book.setBookId(1); book.setInitCategories(1); Book b = this.bookDao.getBook(book ); System.out.println(b.getBookName()); System.out.println(b.getCategories()); } /** * book.hbm.xml inverse=fasle * category.hbm.xml inverse=true * 数据添加正常 * 书籍表、桥接表各新增一条数据 */ @Test public void test1() { Book book = new Book(); book.setBookName("斗破苍穹"); book.setPrice(10f); Category category = new Category(); category.setCategoryId(1); // 直接将category对象加入到新建的book中是错误的，因为此时的category是临时态的，hibernate是不会管理的 // book.getCategories().add(category); Category c = this.bookDao.getCategory(category); // c.getBooks().add(book); book.getCategories().add(c); this.bookDao.addBook(book); } /** * book.hbm.xml inverse=true * category.hbm.xml inverse=true * 只增加书籍表数据 * 桥接表不加数据 * 原因：双方都没有去维护关系 */ @Test public void test2() { Book book = new Book(); book.setBookName("斗帝大罗"); book.setPrice(10f); Category category = new Category(); category.setCategoryId(5); Category c = this.bookDao.getCategory(category); book.getCategories().add(c); this.bookDao.addBook(book); // c.getBooks().add(book); } //测试分页 @Test public void testList1() { Book book = new Book(); PageBean pageBean = new PageBean(); // pageBean.setPage(2); book.setBookName("%圣墟%"); List<Book> list = this.bookDao.list1(book, pageBean); for (Book b : list) { System.out.println(b); } } @Test public void testList2() { Book book = new Book(); PageBean pageBean = new PageBean(); pageBean.setPagination(false); // pageBean.setPage(2); // book.setBookName("%圣墟%"); List<Book> list = this.bookDao.list2(book, pageBean); for (Book b : list) { System.out.println(b); } } }