## 兩種批量查詢的方式 1. Query : 使用這種方式查詢,又被稱作HQL查詢. 2. Criteria : 使用這種方式查詢,又被稱做QBC查詢. ## HQL查詢 ### 條件查 ~~~ //條件查詢,類似SQL語句,但是不是SQL.from的是持久化類,不是表名. Query query = session.createQuery("from Customer where cust_name like ?"); query.setParameter(0,"%j%"); List<Customer> list = query.list(); for (Customer c : list) { System.out.println(c); } ~~~ ### 分頁查 ~~~ Query query = session.createQuery("from Customer"); //起始數據 query.setFirstResult(2); //設置條數 query.setMaxResults(5); List<Customer> list = query.list(); for (Customer c : list) { System.out.println(c); } ~~~ ### 單列查 ~~~ //cust_id是屬性,不是字段名 Query query = session.createQuery("select cust_id from Customer"); List<Object> list = query.list(); //返回的是Object for (Object o : list) { System.out.println(o); } ~~~ ### 多列查 ~~~ Query query = session.createQuery("select cust_id,cust_name from Customer"); List<Object[]> list = query.list(); //list每一項是一個數組 for (Object[] o : list) { System.out.println(Arrays.toString(o)); } ~~~ ### 投影查詢 兩個條件: 1. 查多少個字段持久化類構造函數就需要寫多少個屬性. 2. 語法書寫: select new Customer(cust_id,cust_name) from Customer; ~~~ //投影查詢 Query query = session.createQuery("select new Customer(cust_id,cust_name) from Customer"); List<Customer> list = query.list(); for (Customer c : list) { System.out.println(c); } ~~~ ### 排序查 ~~~ Query query = session.createQuery("select new Customer(cust_id,cust_name) from Customer order by cust_id desc"); List<Customer> list = query.list(); for (Customer c : list) { System.out.println(c); } ~~~ ### 聚合查詢 ~~~ Query query = session.createQuery("select count(*) from Customer"); Object o = query.uniqueResult(); System.out.println(o); ~~~ ## QBC查詢