【JAVAEE學習筆記】hibernate04：查詢種類、HQL、Criteria、查詢優化和練習為客戶列表增加查詢條件
阿新 • • 發佈：2017-06-07
沒有 arrays getpara tex response 寫法 sum exceptio 提高 
一、查詢種類
1.oid查詢-get
2.對象屬性導航查詢
3.HQL
4.Criteria
5.原生SQL
二、查詢-HQL語法
//學習HQL語法 public class Demo { //基本語法 @Test public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //----------------------------------------------------學習HQL語法String hql = " from cn.itcast.domain.Customer ";//完整寫法 String hql2 = " from Customer "; //簡單寫法 String hql3 = " from java.lang.Object "; Query query = session.createQuery(hql3); List list = query.list(); System.out.println(list);//---------------------------------------------------- tx.commit(); session.close(); } @Test //排序 public void fun2(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //----------------------------------------------------String hql1 = " from cn.itcast.domain.Customer order by cust_id asc ";//完整寫法 String hql2 = " from cn.itcast.domain.Customer order by cust_id desc ";//完整寫法 Query query = session.createQuery(hql2); List list = query.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //條件查詢 public void fun3(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql1 = " from cn.itcast.domain.Customer where cust_id =? ";//完整寫法 String hql2 = " from cn.itcast.domain.Customer where cust_id = :id ";//完整寫法 Query query = session.createQuery(hql2); // query.setParameter(0, 2l); query.setParameter("id", 2l); List list = query.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //分頁查詢 public void fun4(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql1 = " from cn.itcast.domain.Customer ";//完整寫法 Query query = session.createQuery(hql1); //limit ?,? // (當前頁數-1)*每頁條數 query.setFirstResult(2); query.setMaxResults(2); List list = query.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //統計查詢 //count 計數 //sum 求和 //avg 平均數 //max //min public void fun5(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql1 = " select count(*) from cn.itcast.domain.Customer ";//完整寫法 String hql2 = " select sum(cust_id) from cn.itcast.domain.Customer ";//完整寫法 String hql3 = " select avg(cust_id) from cn.itcast.domain.Customer ";//完整寫法 String hql4 = " select max(cust_id) from cn.itcast.domain.Customer ";//完整寫法 String hql5 = " select min(cust_id) from cn.itcast.domain.Customer ";//完整寫法 Query query = session.createQuery(hql5); Number number = (Number) query.uniqueResult(); System.out.println(number); //---------------------------------------------------- tx.commit(); session.close(); } @Test //投影查詢 public void fun6(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql1 = " select cust_name from cn.itcast.domain.Customer "; String hql2 = " select cust_name,cust_id from cn.itcast.domain.Customer "; String hql3 = " select new Customer(cust_id,cust_name) from cn.itcast.domain.Customer "; Query query = session.createQuery(hql3); List list = query.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } }
public class Demo2 { //回顧-原生SQL // 交叉連接-笛卡爾積(避免) // select * from A,B // 內連接 // |-隱式內連接 // select * from A,B where b.aid = a.id // |-顯式內連接 // select * from A inner join B on b.aid = a.id // 外連接 // |- 左外 // select * from A left [outer] join B on b.aid = a.id // |- 右外 // select * from A right [outer] join B on b.aid = a.id //--------------------------------------------------------------------- //HQL的多表查詢 //內連接(迫切) //外連接 // |-左外(迫切) // |-右外(迫切) @Test //HQL 內連接 => 將連接的兩端對象分別返回.放到數組中. public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = " from Customer c inner join c.linkMens "; Query query = session.createQuery(hql); List<Object[]> list = query.list(); for(Object[] arr : list){ System.out.println(Arrays.toString(arr)); } //---------------------------------------------------- tx.commit(); session.close(); } @Test //HQL 迫切內連接 => 幫我們進行封裝.返回值就是一個對象 public void fun2(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = " from Customer c inner join fetch c.linkMens "; Query query = session.createQuery(hql); List<Customer> list = query.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //HQL 左外連接 => 將連接的兩端對象分別返回.放到數組中. public void fun3(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = " from Customer c left join c.linkMens "; Query query = session.createQuery(hql); List<Object[]> list = query.list(); for(Object[] arr : list){ System.out.println(Arrays.toString(arr)); } //---------------------------------------------------- tx.commit(); session.close(); } @Test //HQL 右外連接 => 將連接的兩端對象分別返回.放到數組中. public void fun4(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = " from Customer c right join c.linkMens "; Query query = session.createQuery(hql); List<Object[]> list = query.list(); for(Object[] arr : list){ System.out.println(Arrays.toString(arr)); } //---------------------------------------------------- tx.commit(); session.close(); } }學習HQL語法(不常用) - 多表查詢語法
三、查詢-Criteria語法
public class Demo { @Test //基本語法 public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Criteria c = session.createCriteria(Customer.class); List<Customer> list = c.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //條件語法 public void fun2(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Criteria c = session.createCriteria(Customer.class); // c.add(Restrictions.idEq(2l)); c.add(Restrictions.eq("cust_id",2l)); List<Customer> list = c.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //分頁語法 - 與HQL一樣 public void fun3(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Criteria c = session.createCriteria(Customer.class); //limit ?,? c.setFirstResult(0); c.setMaxResults(2); List<Customer> list = c.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //排序語法 public void fun4(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Criteria c = session.createCriteria(Customer.class); c.addOrder(Order.asc("cust_id")); //c.addOrder(Order.desc("cust_id")); List<Customer> list = c.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } @Test //統計語法 public void fun5(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Criteria c = session.createCriteria(Customer.class); //設置查詢目標 c.setProjection(Projections.rowCount()); List list = c.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } }學習Criteria語法
非離線
離線
public class Demo2 { @Test public void fun1(){ //Service/web層 DetachedCriteria dc = DetachedCriteria.forClass(Customer.class); dc.add(Restrictions.idEq(6l));//拼裝條件(全部與普通Criteria一致) //---------------------------------------------------- Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Criteria c = dc.getExecutableCriteria(session); List list = c.list(); System.out.println(list); //---------------------------------------------------- tx.commit(); session.close(); } }學習離線Criteria
四、查詢優化
類級別查詢
get方法:沒有任何策略.調用即立即查詢數據庫加載數據.
load方法: 應用類級別的加載策略
public class Demo { @Test // get方法 : 立即加載.執行方法時立即發送sql語句查詢結果 public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Customer c = session.get(Customer.class, 2l); System.out.println(c); //---------------------------------------------------- tx.commit(); session.close(); } @Test // load方法(默認):是在執行時,不發送任何sql語句.返回一個對象.使用該對象時,才執行查詢. // 延遲加載: 僅僅獲得沒有使用.不會查詢.在使用時才進行查詢. // 是否對類進行延遲加載: 可以通過在class元素上配置lazy屬性來控制. //lazy:true 加載時,不查詢.使用時才查詢b //lazy:false 加載時立即查詢. public void fun2(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Customer c = session.load(Customer.class, 2l); //---------------------------------------------------- tx.commit(); session.close(); System.out.println(c); } }懶加載|延遲加載
public class Demo { //集合級別的關聯 //fetch:select 單表查詢 //lazy:true 使用時才加載集合數據. @Test public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Customer c = session.get(Customer.class, 2l); Set<LinkMan> linkMens = c.getLinkMens();//關聯級別 System.out.println(linkMens); //---------------------------------------------------- tx.commit(); session.close(); } //集合級別的關聯 //fetch:select 單表查詢 //lazy:false 立即記載集合數據 @Test public void fun2(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Customer c = session.get(Customer.class, 2l); Set<LinkMan> linkMens = c.getLinkMens();//關聯級別 System.out.println(linkMens); //---------------------------------------------------- tx.commit(); session.close(); } //集合級別的關聯 //fetch:select 單表查詢 //lazy:extra 極其懶惰.與懶加載效果基本一致. 如果只獲得集合的size.只查詢集合的size(count語句) @Test public void fun3(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Customer c = session.get(Customer.class, 2l); Set<LinkMan> linkMens = c.getLinkMens();//關聯級別 System.out.println(linkMens.size()); System.out.println(linkMens); //---------------------------------------------------- tx.commit(); session.close(); } //集合級別的關聯 //fetch:join 多表查詢 //lazy:true|false|extra 失效.立即加載. @Test public void fun4(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- Customer c = session.get(Customer.class, 2l); Set<LinkMan> linkMens = c.getLinkMens();//關聯級別 System.out.println(linkMens.size()); System.out.println(linkMens); //---------------------------------------------------- tx.commit(); session.close(); } @Test //fetch: subselect 子查詢 //lazy: true 懶加載 public void fun5(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = "from Customer"; Query query = session.createQuery(hql); List<Customer> list = query.list(); for(Customer c:list){ System.out.println(c); System.out.println(c.getLinkMens().size()); System.out.println(c.getLinkMens()); } //---------------------------------------------------- tx.commit(); session.close(); } @Test //fetch: subselect 子查詢 //lazy: false 立即加載 public void fun6(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = "from Customer"; Query query = session.createQuery(hql); List<Customer> list = query.list(); for(Customer c:list){ System.out.println(c); System.out.println(c.getLinkMens().size()); System.out.println(c.getLinkMens()); } //---------------------------------------------------- tx.commit(); session.close(); } @Test //fetch: subselect 子查詢 //lazy: extra 極其懶惰 public void fun7(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = "from Customer"; Query query = session.createQuery(hql); List<Customer> list = query.list(); for(Customer c:list){ System.out.println(c); System.out.println(c.getLinkMens().size()); System.out.println(c.getLinkMens()); } //---------------------------------------------------- tx.commit(); session.close(); } }關聯級別 延遲加載 & 抓取策略（客戶再獲取多個聯系人）
public class Demo2 { @Test //fetch:select 單表查詢 //lazy:proxy //customer-true 懶加載 public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- LinkMan lm = session.get(LinkMan.class, 3l); Customer customer = lm.getCustomer(); System.out.println(customer); //---------------------------------------------------- tx.commit(); session.close(); } @Test //fetch:join 多表 //lazy: 失效 public void fun3(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- LinkMan lm = session.get(LinkMan.class, 3l); Customer customer = lm.getCustomer(); System.out.println(customer); //---------------------------------------------------- tx.commit(); session.close(); } @Test //fetch:select 單表查詢 //lazy:proxy //customer-false 立即加載 public void fun2(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- LinkMan lm = session.get(LinkMan.class, 3l); Customer customer = lm.getCustomer(); System.out.println(customer); //---------------------------------------------------- tx.commit(); session.close(); } }關聯級別 延遲加載 & 抓取策略（通過聯系人獲得客戶）
結論:為了提高效率.fetch的選擇上應選擇select. lazy的取值應選擇 true. 全部使用默認值.
no-session問題解決: 擴大session的作用範圍.
public class Demo { @Test public void fun1(){ Session session = HibernateUtils.openSession(); Transaction tx = session.beginTransaction(); //---------------------------------------------------- String hql = "from Customer "; Query query = session.createQuery(hql); List<Customer> list = query.list(); for(Customer c:list){ System.out.println(c.getLinkMens()); } //---------------------------------------------------- tx.commit(); session.close(); } }抓取數量
五、練習:為客戶列表增加查詢條件
在上一次筆記的代碼基礎上，在顯示客戶列表之前，加入篩選的條件:
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1獲得查詢條件 String cust_name = request.getParameter("cust_name"); //2判斷查詢條件是否不為空 DetachedCriteria dc = DetachedCriteria.forClass(Customer.class); if(cust_name!=null && !"".equals(cust_name)){ dc.add(Restrictions.like("cust_name", "%"+cust_name+"%")); } //不為空=>添加條件 //3 調用Service查詢所有客戶 List<Customer> list = cs.getAll(dc); //4 將客戶列表放入request域 request.setAttribute("list", list); //5 轉發到list.jsp顯示 request.getRequestDispatcher("/jsp/customer/list.jsp").forward(request, response); }Servlet層代碼
public List<Customer> getAll(DetachedCriteria dc) { Session session = HibernateUtils.getCurrentSession(); //打開事務 Transaction tx = session.beginTransaction(); List<Customer> list = customerDao.getAll(dc); //關閉事務 tx.commit(); return list; }Service層代碼
public List<Customer> getAll(DetachedCriteria dc) { //1 獲得session Session session = HibernateUtils.getCurrentSession(); //2 將離線對象關聯到session Criteria c = dc.getExecutableCriteria(session); //3 執行查詢並返回 return c.list(); }Dao層代碼
【JAVAEE學習筆記】hibernate04：查詢種類、HQL、Criteria、查詢優化和練習為客戶列表增加查詢條件