Scenario: query the customer according to the customer id, and find out all contacts of the customer

 @Test
    public void selectTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Find out the customer according to C ﹣ ID
            Customer customer = session.get(Customer.class,1);
            //Then find out the contact person of the customer
            Set<Salesperson> set  = customer.getSalespersonSet();
            Iterator<Salesperson> it = set.iterator();
            while (it.hasNext()) {
                Salesperson str = it.next();
                System.out.println(str.getS_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• Query all customer information
  • Create Query object and write out hql statement
  • Call the method in the query object to get the result
  • Query all from + entity class names

    @Test
    public void selectTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Create query object
              Query query =  session.createQuery("from Customer");

             //Call method to get result
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• Condition query
  • Statement: from entity class name where entity class property =? and entity class name

@Test
    public void selectByCidAndCnameTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Create query object
            Query query =  session.createQuery("from Customer where c_id = ? and c_name = ?");
            query.setParameter(0,1);
            query.setParameter(1,"Li customer");
            //Call method to get result
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

Condition query

• Sort query
  • Statement: from entity class name order by entity class name asc/desc

@Test
    public void selectOrderByTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Create query object
            Query query =  session.createQuery("from Customer order by  c_id desc ");
            //Call method to get result
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• Paging query

 @Test
    public void selectLimitTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Create query object
            Query query =  session.createQuery("from Customer");
            //Set paging data
            query.setFirstResult(0);
            query.setMaxResults(2);
            //Call method to get result
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• Projection query
  • Statement: select * from entity class attribute name 1, entity class attribute name 2, from entity class name
  • Cannot write * after select, not supported

 @Test
    public void selectSomeTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Create query object
            Query query =  session.createQuery("select c_name from Customer");
            //Call method to get result
            List<Object> lists = query.list();
            for (Object list: lists) {
                System.out.println(list);
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

image.png

• Aggregate function use
  • count ，sum , avg , mac , min
  • Statement: select count (*) from entity class name

@Test
    public void selectHanshuTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //Create query object
            Query query =  session.createQuery("select count(*) from Customer");
            //Call method to get result
            Object count = query.uniqueResult();
            //Convert to long, then int
            Long co = Long.parseLong(count.toString());
            System.out.println(co.intValue());
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }