Hibernate学习-11-几种查询详解

1）Get/load主键查询

  //1)主键查询

  // Dept dept = (Dept)session.load(Dept.class,1);

  // Dept dept = (Dept)session.get(Dept.class,1); 

     System.out.println(dept);

结果

Hibernate:
    select
        dept0_.deptId as deptId0_0_,
        dept0_.deptName as deptName0_0_
    from
        t_dept dept0_
    where
        dept0_.deptId=?
[email protected]

2) 对象导航查询

        //2)对象导航查询
        Dept dept = (Dept)session.get(Dept.class,1);
        System.out.println(dept.getEmployees());

结果

Hibernate:
    select
        dept0_.deptId as deptId0_0_,
        dept0_.deptName as deptName0_0_
    from
        t_dept dept0_
    where
        dept0_.deptId=?
Hibernate:
    select
        employees0_.dept_id as dept4_0_1_,
        employees0_.empId as empId1_,
        employees0_.empId as empId1_0_,
        employees0_.empName as empName1_0_,
        employees0_.salary as salary1_0_,
        employees0_.dept_id as dept4_1_0_
    from
        t_employee employees0_
    where
        employees0_.dept_id=?
[[email protected], [email protected]]

3)HQL查询

使用hql查询的时候，映射文件auto-import="true"要设置为true,如果是false，在写hql的时候，要指定类的全名。

     //3)HQL查询
     //a查询全部列

     Query q = session.createQuery("from Employee");
     System.out.println(q.list());
     //b查询指定列
     Query q = session.createQuery("select d.deptId , d.deptName from Dept d");     System.out.println(q.list());
     //c查询指定列，自动封装为对象(必须提供有参数的构造器)
        Query q = session.createQuery("select new Dept(d.deptId,d.deptName) from Dept d");
     System.out.println(((Dept)q.list().get(0)).getDeptName());

     //d 条件查询

     //条件查询-占位符
     Query q = session.createQuery("from Dept d where deptName = ?");
        // q.setString(0,"综合部");
     q.setParameter(0,"综合部");
     System.out.println(q.list());

     //条件查询，命名参数
     Query q = session.createQuery("from Dept d where deptId=:myId or deptName=:name");
     q.setParameter("myId",1);
     q.setParameter("name","综合部");
     System.out.println(q.list());

        //范围
     Query q = session.createQuery("from Dept d where deptId between ? and ?");
     q.setParameter(0,1);
     q.setParameter(1,6);
     System.out.println(q.list());

     //模糊查询     Query  q = session.createQuery("from Dept d where deptName like ?");     q.setString(0,"%部%");     System.out.println(q.list());

     //e.聚合函数统计
     Query q = session.createQuery("select count (*) from Dept");
     Long num = (Long)q.uniqueResult();
     System.out.println(num);

     //分组查询，统计每个部门的人数
     Query q = session.createQuery("select e.dept , count(*) from Employee e group by e.dept");

     System.out.println(q.list());