什么是hql？ HQL是Hibernate Query Language的缩写。 HQL（Hibernate Query Language），即Hibernate的查询语言跟SQL非常相像。不过HQL与SQL的最根本的区别，就是它是面向对象的。
注意： 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
hql中使用占位符 ?占位符 从下标0开始计算位置 hibernate5之后不再支持?占位符
:命名参数
处理返回的结果集 HqlTest类
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 * * hql * 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); } } ```HQL的分页工具类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
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
/** * 1. 设置参数的问题 * 2. 分页代码重复的问题 * @author _AluoKa * */ public class BaseDao { /** * 通用的参数设值方法 * 参数键值对集合 * 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.setParameter(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); } /** * 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; } }BookDao 需要继承BaseDao 。
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： * 写一个带查询的并且能 分页方法 * @param book * @param pageBean */ 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 query=session.createQuery(hql); //query相当于前面SQL所用的prepareStatement if(StringUtils.isNotBlank(bookName)){ query.setParameter("bookName", bookName); } //通过上述代码会发现，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测试
@Test public void testList2() { Book book=new Book(); PageBean pageBean=new PageBean(); // pageBean.setPage(2); // pageBean.setPagination(false); book.setBookName("%圣墟%"); List<Book> list=this.bookDao.list2(book, pageBean); for (Book b : list) { System.out.println(b); } }