一、对象导航查询
之前的客户和联系人的关系是一 对多的关系：一对多
场景：根据客户id查询客户，在查出该客户的所有联系人
@Test
public void selectTest(){
SessionFactory sessionFactory = null;
Session session = null;
Transaction transaction = null;
try{
sessionFactory = HibernateUtils.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
//根据c_id 查询出该客户
Customer customer = session.get(Customer.class,1);
//然后查询出该客户联系人
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();
}
}
二、HQL查询
- 查询所有客户信息
- 创建Query对象，写出hql语句
- 调用query对象里面的方法得到结果
- 查询所有 from+实体类名称
@Test
public void selectTest(){
SessionFactory sessionFactory = null;
Session session = null;
Transaction transaction = null;
try{
sessionFactory = HibernateUtils.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
//创建query对象
Query query = session.createQuery("from Customer");
//调用方法得到结果
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();
}
}
- 条件查询
- 语句：from 实体类名称 where 实体类属性=？ and 实体类名称
@Test
public void selectByCidAndCnameTest(){
SessionFactory sessionFactory = null;
Session session = null;
Transaction transaction = null;
try{
sessionFactory = HibernateUtils.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
//创建query对象
Query query = session.createQuery("from Customer where c_id = ? and c_name = ?");
query.setParameter(0,1);
query.setParameter(1,"李客户");
//调用方法得到结果
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();
}
}
条件查询
- 排序查询
- 语句：from 实体类名称 order by 实体类名称 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();
//创建query对象
Query query = session.createQuery("from Customer order by c_id desc ");
//调用方法得到结果
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();
}
}
- 分页查询
@Test
public void selectLimitTest(){
SessionFactory sessionFactory = null;
Session session = null;
Transaction transaction = null;
try{
sessionFactory = HibernateUtils.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
//创建query对象
Query query = session.createQuery("from Customer");
//设置分页数据
query.setFirstResult(0);
query.setMaxResults(2);
//调用方法得到结果
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();
}
}
- 投影查询
- 语句：select * from 实体类属性名称一，实体类属性名称二， from 实体类名称
- select 后面不能写 * 号，不支持
@Test
public void selectSomeTest(){
SessionFactory sessionFactory = null;
Session session = null;
Transaction transaction = null;
try{
sessionFactory = HibernateUtils.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
//创建query对象
Query query = session.createQuery("select c_name from Customer");
//调用方法得到结果
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
- 聚集函数使用
- count ，sum , avg , mac , min
- 语句：select count(*) from 实体类名称
@Test
public void selectHanshuTest(){
SessionFactory sessionFactory = null;
Session session = null;
Transaction transaction = null;
try{
sessionFactory = HibernateUtils.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
//创建query对象
Query query = session.createQuery("select count(*) from Customer");
//调用方法得到结果
Object count = query.uniqueResult();
//先转换成long类型，再转换为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();
}
}
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