Hibernate之查询

一、HQL查询：通过HQL语句进行查询，HQL语句中没有与数据库相关的任何东西。

1.根据HQL取对象的集合,使用Query的list();方法

public void getList(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String hql = "from Customer";Query query = session.createQuery(hql);List<Customer> list = query.list();for (Customer customer : list) {System.out.println(customer);} transaction.commit();session.close();}

2.根据HQL取单个对象，使用Query的uniqueResult();

public void getOne(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String Hql = "from Customer where cust_id = 1";Query query = session.createQuery(Hql);Customer customer = (Customer) query.uniqueResult();System.out.println(customer);transaction.commit();session.close();}

3. “?”占位符来选择查询条件，查询的条件为对象中的字段，通过Query的setParmeter(int position,Object val);进行对条件的赋值

public void getSth(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String Hql = "from Customer where cust_id = ?";Query query = session.createQuery(Hql);//query.setLong(0, 1L);query.setParameter(0, 2l);//不知道类型的时候使用Customer customer = (Customer) query.uniqueResult();System.out.println(customer);transaction.commit();session.close();}

4.命名占位符，“：+对象属性名”，冒号加对象属性名表示查询对象的字段命名，然后通过Query的setParmeter(String name,Object val);方法进行赋值

ublic void getSthByName(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String Hql = "from Customer where cust_id = :this_is_cust_id";Query query = session.createQuery(Hql);query.setParameter("this_is_cust_id", 2l);//直接定义占位符名称，不需要数这个第几个位置Customer customer = (Customer) query.uniqueResult();System.out.println(customer);transaction.commit();session.close();}

5.设置分页，类似于mysql 的limit，通过Query的setFirstResult(int start);方法设置起始位置，setMaxResult(int eachTotal);方法设置每页的数据个数

public void getAllByEach(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String Hql = "from Customer";Query query = session.createQuery(Hql);query.setFirstResult(1);query.setMaxResults(1);List<Customer> list = query.list();System.out.println(list);transaction.commit();session.close();}

二、Criteria查询

1.通过session的createCriteria(Class class);方法获取的Criteria，之后方法与Query一致

public void getAll(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();Criteria criteria = session.createCriteria(Customer.class);List<Customer> list = criteria.list();System.out.println(list);transaction.commit();session.close();}

2.根据条件查询单条,通过Criteria的add(条件)来添加查询条件，Restrictions类提供了多种查询条件

public void getOne(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();Criteria criteria = session.createCriteria(Customer.class);criteria.add(Restrictions.eq("cust_id", 1L));Customer customer = (Customer) criteria.uniqueResult();System.out.println(customer);transaction.commit();session.close();}

3.聚合函数，通过Criteria的setProjection(条件);方法设置聚合函数的内容，例如求Customer的总条数

public void getAllCount(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();Criteria criteria = session.createCriteria(Customer.class);criteria.setProjection(Projections.rowCount());Long count = (Long) criteria.uniqueResult();System.out.println(count);transaction.commit();session.close();}

三、原生SQL查询

1.通过SQLQuery来进行对数据库的SQL语句方式的查询，此方式得到的是一个包含多个数组的list，一条记录为一个数组

public void getAll(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String sql = "select * from cst_customer";SQLQuery query = session.createSQLQuery(sql);List<Object[]> list = query.list();//得到的一个包含多个数组的list，一条记录为一个数组for (Object[] objects : list) {System.out.println(Arrays.toString(objects));}transaction.commit();session.close();}

2.通过对SQLQuery的addEntity(Class class);方法，可以得到所需类型的list

public void getAllByEntity(){Session session = HibernateUtils.getCurrentSession();Transaction transaction = session.beginTransaction();String sql = "select * from cst_customer";SQLQuery query = session.createSQLQuery(sql);query.addEntity(Customer.class);List<Customer> list = query.list();//得到的一个包含多个数组的list，一条记录为一个数组System.out.println(list);transaction.commit();session.close();}

3.带"?"的占位符的使用方式和前面的HQL的方式一样