一、通過oid查詢

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Customer cs = session.get/load(Customer.class, 1L);　　// load是，等到用的時候才知曉System.out.println(cs);// ----------------------------------------tx.commit();session.close(); }

二、HQL查詢

1、基本查詢

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql = "from Customer";Query query = session.createQuery(hql);List<Customer> list = query.list(); // 獲取所有數據//Customer cs = (Customer) query.uniqueResult(); // 獲取單條數據（只有一條才能使用）System.out.println(list);// ----------------------------------------tx.commit();session.close(); }

2、條件查詢

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql1 = "from Customer where cust_id=?"; // ?占位符String hql2 = "from Customer where cust_id=:id"; // 命名占位符Query query = session.createQuery(hql2);// query.setParameter(0,2L);query.setParameter("id",2L);// List<Customer> list = query.list(); // 獲取所有數據Customer cs = (Customer) query.uniqueResult(); // 獲取單條數據（只有一條才能使用）System.out.println(cs);// ----------------------------------------tx.commit();session.close(); }

3、排序

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql1 = "from Customer order by cust_id asc"; // 正序排String hql2 = "from Customer order by cust_id desc"; // 逆序排Query query = session.createQuery(hql1);List<Customer> list = query.list();System.out.println(list);// ----------------------------------------tx.commit();session.close(); }

4、分頁查詢

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql = "from Customer";Query query = session.createQuery(hql);query.setFirstResult(1);query.setMaxResults(3);List<Customer> li = query.list();System.out.println(li);// ----------------------------------------tx.commit();session.close(); }

5、聚合查詢

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql1 = "select count (*) from Customer "; // 返回影響數（row）String hql2 = "select max (cust_id) from Customer "; // 最大值String hql3 = "select min (cust_id) from Customer "; // 最小值String hql4 = "select avg (cust_id) from Customer "; // 平均值String hql5 = "select sum (cust_id) from Customer "; // 求和Query query = session.createQuery(hql4);Number num = (Number) query.uniqueResult();System.out.println(num);// ----------------------------------------tx.commit();session.close(); }

6、投影查詢

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql = "select cust_id,cust_name from Customer ";Query query = session.createQuery(hql);List li = query.list();System.out.println(li);// ----------------------------------------tx.commit();session.close(); }

7、多表查詢

SQL的多表查詢

交叉連接-笛卡爾積（最好不要用，會查出重復數據）內連接|-隱式內連接select * from A,B where b.aid=a.id|-顯示內連接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（一般不用，還不如用原生SQL呢）

1、內連接

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql = "from Customer c inner join c.linkMens";Query query = session.createQuery(hql);List<Object[]> li = query.list();for(Object[] o : li){System.out.println(Arrays.toString(o));}// ----------------------------------------tx.commit();session.close(); }

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[Customer [cust_id=1, cust_name=鑫哥論文], LinkMan{lkm_id=5, lkm_name='tom'}]
[Customer [cust_id=1, cust_name=鑫哥論文], LinkMan{lkm_id=6, lkm_name='è??é??'}]
[Customer [cust_id=1, cust_name=鑫哥論文], LinkMan{lkm_id=7, lkm_name='計震宇'}]

2、內連接迫切

查詢語句上多了個fetch，返回的是Customer對象

public void func1(){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> li = query.list();System.out.println(li);// ----------------------------------------tx.commit();session.close(); }

[Customer{cust_id=1, cust_name='百度公司', linkMens=[LinkMan{lkm_id=1, lkm_name='于佳鑫'}, LinkMan{lkm_id=6, lkm_name='è??é??'}]}, Customer{cust_id=2, cust_name='谷歌公司', linkMens=[LinkMan{lkm_id=3, lkm_name='張寶巖'}]}, Customer{cust_id=3, cust_name='360', linkMens=[LinkMan{lkm_id=4, lkm_name='tom'}]}, Customer{cust_id=4, cust_name='快播', linkMens=[LinkMan{lkm_id=5, lkm_name='tom'}]}, Customer{cust_id=1, cust_name='百度公司', linkMens=[LinkMan{lkm_id=1, lkm_name='于佳鑫'}, LinkMan{lkm_id=6, lkm_name='è??é??'}]}]

3、左/右 外連接（迫切）

@Test public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------String hql = "from Customer c left join c.linkMens";Query query = session.createQuery(hql);List<Object []> li = query.list();for (Object [] o : li){System.out.println(Arrays.toString(o));}// ----------------------------------------tx.commit();session.close(); }

三、Criteria查詢

1、基本查詢

public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Criteria criteria = session.createCriteria(Customer.class);List list = criteria.list();System.out.println(list);// ----------------------------------------tx.commit();session.close(); }

2、條件查詢

public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Criteria criteria = session.createCriteria(Customer.class);criteria.add(Restrictions.eq("cust_id",2L)); // 添加查詢條件//List list = criteria.list();Customer result = (Customer) criteria.uniqueResult();System.out.println(result);// ----------------------------------------tx.commit();session.close(); }

3、分頁查詢

public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Criteria criteria = session.createCriteria(Customer.class);criteria.setFirstResult(2);criteria.setMaxResults(3);List<Customer> list = criteria.list();System.out.println(list);// ----------------------------------------tx.commit();session.close(); }

4、排序

public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Criteria criteria = session.createCriteria(Customer.class);criteria.addOrder(Order.asc("cust_id")); // 正序criteria.addOrder(Order.desc("cust_id")); // 逆序List<Customer> list = criteria.list();System.out.println(list);// ----------------------------------------tx.commit();session.close(); }

5、聚合運算

public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Criteria criteria = session.createCriteria(Customer.class);criteria.setProjection(Projections.rowCount()); // 查詢總和Number num = (Number) criteria.uniqueResult();System.out.println(num);// ----------------------------------------tx.commit();session.close(); }

離線查詢

非離線

離線（dao層可以不用變，我們在前面構造好查詢條件就行了）

代碼實現

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四、查詢優化

load方法，當使用時，才進行SQL查詢

實際上，load方法是將Customer對象變成超級Customer對象，可以查詢數據庫，當調用后（查詢數據庫后），變成了普通的Customer對象

public void func1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------Customer load = session.load(Customer.class, 2L);System.out.println(load);// ----------------------------------------tx.commit();session.close(); }

它實際上也是依賴session的，所以session.close()后，就會報錯

所以我們可以使用 filter 來解決

動態代理：（打印對象時有$就是代理對象）

給對象搞代理的目的：對方法改造或增強

連接池：
目的：改變連接對象的關閉方法（不能讓連接真的關閉 應該放回連接池），對connection進行代理

解決中文亂碼：
對request對象進行代理，改造getParameterMap()...方法，變成沒有亂碼的

類級別 延遲加載：
將Customer對象變成超級Customer對象，可以查詢數據庫

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轉載于:https://www.cnblogs.com/x54256/p/8470045.html

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