Hibernate(3)hql查询

目录

查询所有对象

条件查询

使用带问号站位符的条件查询

使用命名占位符的条件查询

分页查询

---

使用环境:多表查询，条件不复杂时使用

查询所有对象

@Test
public void test4(){
    Session session = HibernateUtils.getCurrentSession();
    Transaction tx = session.beginTransaction();
    //~~~~~~~~~~~~~~~~~
    //1.书写Hql   可以书写完整的类名，如果类名在项目中唯一也可以简写 如果是查询对象所有信息，即select *  则可以省略
    //string hql = "from com.ycsj.domain.Customer";   //书写完整类型  省略select * 
    String hql = "from Customer";       //项目中唯一类名  
    //2.根据hql创建查询对象
    Query query = session.createQuery(hql);
    //3.查询
    //返回list结果
    List<Customer> list = query.list();
    //返回单个对象
    //query.uniqueResult();
    System.out.println(list);


    //~~~~~~~~~~~~~~
    tx.commit();

}

条件查询

/**
 * 条件查询
 * 在hql语句中不会出现数据库相关的信息 条件中where子句查询的是实体类中的字段
 */
@Test
public void test5(){
    Session session = HibernateUtils.getCurrentSession();
    Transaction tx = session.beginTransaction();
    //~~~~~~~~~~~~~~~~~
    //1.书写Hql
    //string hql = "from com.ycsj.domain.Customer";
    String hql = "from Customer where cust_id=1";
    //2.根据hql创建查询对象
    Query query = session.createQuery(hql);
    //3.查询
    //返回list结果
   // List<Customer> list = query.list();
    //返回单个对象
    Customer custormer = (Customer) query.uniqueResult();
    System.out.println(custormer);


    //~~~~~~~~~~~~~~
    tx.commit();

}

使用带问号站位符的条件查询

/**
 * 条件查询
 * 问号占位符 在新版本的hibernate框架中使用？+数字 来替代，原来的问号
 */
@Test
public void test6(){
    Session session = HibernateUtils.getCurrentSession();
    Transaction tx = session.beginTransaction();
    //~~~~~~~~~~~~~~~~~
    //1.书写Hql
    //string hql = "from com.ycsj.domain.Customer";
    String hql = "from Customer where cust_id=?0";
    //2.根据hql创建查询对象
    Query query = session.createQuery(hql);
    //设置参数
    query.setParameter(0,1);

    //3.查询
    //返回list结果
    // List<Customer> list = query.list();
    //返回单个对象
    Customer custormer = (Customer) query.uniqueResult();
    System.out.println(custormer);


    //~~~~~~~~~~~~~~
    tx.commit();

}

使用命名占位符的条件查询

/**
 * 条件查询
 * 命名占位符:+命名    
 */
@Test
public void test7(){
    Session session = HibernateUtils.getCurrentSession();
    Transaction tx = session.beginTransaction();
    //~~~~~~~~~~~~~~~~~
    //1.书写Hql
    //string hql = "from com.ycsj.domain.Customer";
    String hql = "from Customer where cust_id=:cust_id";
    //2.根据hql创建查询对象
    Query query = session.createQuery(hql);
    //设置参数
    query.setParameter("cust_id",1);   //与上面的命名相对应 

    //3.查询
    //返回list结果
    // List<Customer> list = query.list();
    //返回单个对象
    Customer custormer = (Customer) query.uniqueResult();
    System.out.println(custormer);


    //~~~~~~~~~~~~~~
    tx.commit();

}

分页查询

/**
 * 分页查询
 */
@Test
public void test8(){
    Session session = HibernateUtils.getCurrentSession();
    Transaction tx = session.beginTransaction();
    //~~~~~~~~~~~~~~~~~
    //1.书写Hql
    //string hql = "from com.ycsj.domain.Customer";
    String hql = "from Customer";
    //2.根据hql创建查询对象
    Query query = session.createQuery(hql);
    //设置分页信息
    query.setFirstResult(0);     
    query.setMaxResults(1);
    //3.查询
    //返回list结果
    List<Customer> list = query.list();
    //返回单个对象
    //Customer custormer = (Customer) query.uniqueResult();
    System.out.println(list);


    //~~~~~~~~~~~~~~
    tx.commit();

}

排序

 @Test
    public  void  test1(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~
        String hql = " from LinkMan order by lkm_id asc";
        String hql2 = " from LinkMan order by lkm_id desc";

        Query query = session.createQuery(hql2);
        List<LinkMan> list = query.list();
        System.out.println(list);

        //~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();

    }

聚合函数

//count
    //max
    //min
    //avg
    @Test
    public  void  test2(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~

        String hql = " select count(*) from LinkMan order";
        String hql2 = " select avg(lkm_id) from LinkMan order";
        String hql3 = " select max(lkm_id) from LinkMan order";
        String hql4 = " select min(lkm_id) from LinkMan order";


        Query query = session.createQuery(hql3);
        Number number = (Number) query.uniqueResult();
        System.out.println(number);

        //~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();

    }

投影检索

就是不查询所有 只查询部分字段

 @Test
    public  void  test3(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~

        String hql1 = " select lkm_name from LinkMan";
        String hql2 = " select lkm_id,lkm_name from LinkMan";     //返回数组
        String hql3 = " select new LinkMan(lkm_id,lkm_name) from LinkMan"; //需要在实体类中创建响应的构造函数 自动封装到对象中



        Query query = session.createQuery(hql3);
        //查询某一列，将查询出来的结果封装到一个数组中
        List list = query.list();
        System.out.println(list);

        //~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();

    }

多表查询

/*回顾原生sql
* 交叉连接   ---笛卡尔积
*select * from A,B  A中有m条记录 B中有n条记录 查询结果有m*n条记录 这种情况的应用场景几乎没有
*内连接
*    |----隐式内连接
*         select * from A,B where A.xxx=B.yyy;
*    |----显示内连接
*         select * from A inner join B on B.aid=A.id;        查询交集
* 外连接
*    |----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支持破切查询 fetch

 /**
     * hql多表查询
     * 内连接     将数据封装到数组中
     *
     * [Ljava.lang.Object;@5432c277
     * [Ljava.lang.Object;@15e0fe05
     * [Ljava.lang.Object;@1128620c
     * [Ljava.lang.Object;@6bf13698
     */
    @Test
    public void  test(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~~~~~~~~~~~
        String hql = " from Customer c inner join c.linkMans";

        Query query = session.createQuery(hql);
        List<Object[]> list = query.list();
        for (Object[] arr:list){
            System.out.println(arr);

        }
        //~~~~~~~~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();
    }


    /**
     * 迫切内连接  帮助把数据封装到对象中
     *[Customer{cust_id=1, cust_name='zhiduowa', linkMans=[LinkMan{lkm_id=1, lkm_name='董事长'}, LinkMan{lkm_id=2, lkm_name='总经理'}]}
     */
    @Test
    public void  test1(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~~~~~~~~~~~
        String hql = " from Customer c inner join fetch c.linkMans";

        Query query = session.createQuery(hql);
        List<Customer> list = query.list();
        System.out.println(list);
        //~~~~~~~~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();
    }

    /**
     * 左外连接  左边的数据都会显示
     */
    @Test
    public void  test3(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~~~~~~~~~~~
        String hql = " from Customer c left join c.linkMans";

        Query query = session.createQuery(hql);
        List<Object[]> list = query.list();
        for (Object[] arr:list){
            System.out.println(arr);

        }
        //~~~~~~~~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();
    }


    /**
     * 右外连接  右边的数据都会显示  被连接的数据全部显示 不管有没有对应
     */
    @Test
    public void  test4(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //~~~~~~~~~~~~~~~~~~~~~~~~
        String hql = " from Customer c right join c.linkMans";

        Query query = session.createQuery(hql);
        List<Object[]> list = query.list();
        for (Object[] arr:list){
            System.out.println(arr);

        }
        //~~~~~~~~~~~~~~~~~~~~~~~~
        tx.commit();
        session.close();
    }
}