Hibernate中Query对象执行HQL语句

from子句 查询所有部门

 /**
     * 编写HQL语句 from子句
     */

    public List<Department> from()
    {
        String hql="from Department as dept";
        List<Department> departments=this.getCurrentSession().createQuery(hql).list();
        return departments;
    }

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_

select子句 选取对象属性 选取deptName属性

 /**
     * select子句查询部门名称
     */

    public List<String> selectDeptName()
    {
        String hql="select dept.deptName from Department as dept";
        List<String> deptNames=this.getCurrentSession().createQuery(hql).list();
        return deptNames;
    }

Hibernate:
select
department0_.deptName as col_0_0_
from
project.Department department0_

    /**
     * select子句查询部门所有信息
     */

    public List<Department> selectAllMsg()
    {
        String hql="select dept from Department as dept";
        List<Department> departments=this.getCurrentSession().createQuery(hql).list();
        return departments;

    }

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_

where子句用于表达查询的限制条件

/**
     * where子语句查部门名称是研发部的部门信息
     */
    public List<Department> selectWhere() {
        String hql = "select dept from Department as dept where dept.deptName='研发部'";
        List<Department> departments = this.getCurrentSession().createQuery(hql).list();
        return departments;
    }

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_
where
department0_.deptName='研发部'

使用表达式(函数)

   String hql = "select dept from Department as dept where lower(dept.deptName)='SALES'";

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_
where
lower(department0_.deptName)='SALES'

order by 子句用于按指定属性排序 关键字asc,desc可选，用于指定按照升序或者降序进行排序，默认按升序排序

String hql = "select dept from Department as dept  order by dept.deptNo desc ";

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_
order by
department0_.deptNo desc

Query对象的list()方法查询

 String hql="from Department as dept";
        List<Department> departments = this.getCurrentSession().createQuery(hql).list();

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_

from
    project.Department department0_

Query对象iterate()方法查询

/**
     * iterate方法查询
     */
    public Iterator<Department> iterator() {
        String hql = "from Department as dept";
        Iterator<Department> departments = this.getCurrentSession().createQuery(hql).iterate();
        return departments;

    }

Hibernate:
select
department0_.deptNo as col_0_0_
from
project.Department department0_
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=10, deptName='sales', location='西部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=11, deptName='sales', location='东部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=12, deptName='sales', location='西部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=14, deptName='sales', location='北部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=15, deptName='sales', location='东部'}

list()方法查询和iterate()方法查询的区别

  • 1.返回的接口对象不同: list()方法返回 List接口对象，iterate()方法返回Iterator接口对象
  • 2.执行的遍历输出的地方不同:list()方法可以在会话关闭后遍历输出结果，iterate方法不可以在会话结束后遍历输出结果,不然会抛出Session is Close.的异常。
  • 3.执行的SQL语句不同:list()方法生成一条SQL查询语句,查询所有符合条件的记录;iterate()方法首先查询所有符合条件的主键值，然后在需要某个对象的其他属性值时，才生成按主键查询的SQL语句，即iterate()方法可能生成1+N条SQL语句。
  • 4.是否有一级缓存(Session缓存)一次事务进行多次查询时从Session中取数据而不是从数据库中取数据即集合对象是否由Session管理。list()执行多次SQL语句没有Session缓存；iterate()执行一次SQL语句有Session缓存机制。

效果如下

 Transaction tx = null;
        List<Department> departments = new ArrayList<>();
        List<Department> temp =new ArrayList<>();
        try {
            tx = departmentDao.getCurrentSession().beginTransaction();
            departments = departmentDao.selectWhere();
            for (Department department : departments) {
                System.out.println("部门名称是研发部的部门信息:" + department.toString());
            }
            //一次事务进行多次查询
            temp = departmentDao.selectWhere();
            for (Department department : temp ){
                System.out.println("部门名称是研发部的部门信息:" + department.toString());
            }
            tx.commit();
        } catch (HibernateException ex) {
            ex.printStackTrace();
            if (tx != null) {
                tx.rollback();
            }
        }

Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_
部门名称是研发部的部门信息:Department{deptNo=10, deptName='sales', location='西部'}
部门名称是研发部的部门信息:Department{deptNo=11, deptName='sales', location='东部'}
部门名称是研发部的部门信息:Department{deptNo=12, deptName='sales', location='西部'}
部门名称是研发部的部门信息:Department{deptNo=14, deptName='sales', location='北部'}
部门名称是研发部的部门信息:Department{deptNo=15, deptName='sales', location='东部'}
Hibernate:
select
department0_.deptNo as deptNo0_,
department0_.deptName as deptName0_,
department0_.location as location0_
from
project.Department department0_
部门名称是研发部的部门信息:Department{deptNo=10, deptName='sales', location='西部'}
部门名称是研发部的部门信息:Department{deptNo=11, deptName='sales', location='东部'}
部门名称是研发部的部门信息:Department{deptNo=12, deptName='sales', location='西部'}
部门名称是研发部的部门信息:Department{deptNo=14, deptName='sales', location='北部'}
部门名称是研发部的部门信息:Department{deptNo=15, deptName='sales', location='东部'}

 Transaction tx = null;
        Iterator<Department> departments = null;
        Iterator<Department> temp = null;
        try {
            tx = departmentDao.getCurrentSession().beginTransaction();
            departments = departmentDao.iterator();
            while (departments.hasNext()) {
                Department department = departments.next();
                System.out.println(department);
            }
            System.out.println("----------");
            //一次事务进行多次查询
            temp = departmentDao.iterator();
            while (temp.hasNext()) {
                Department department = temp.next();
                System.out.println(department);
            }
            tx.commit();
        } catch (HibernateException ex) {
            ex.printStackTrace();
            if (tx != null) {
                tx.rollback();
            }
        }
    }

Hibernate:
select
department0_.deptNo as col_0_0_
from
project.Department department0_
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=10, deptName='sales', location='西部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=11, deptName='sales', location='东部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=12, deptName='sales', location='西部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=14, deptName='sales', location='北部'}
Hibernate:
select
department0_.deptNo as deptNo0_0_,
department0_.deptName as deptName0_0_,
department0_.location as location0_0_
from
project.Department department0_
where
department0_.deptNo=?
Department{deptNo=15, deptName='sales', location='东部'}
Hibernate:
select
department0_.deptNo as col_0_0_
from
project.Department department0_
Department{deptNo=10, deptName='sales', location='西部'}
Department{deptNo=11, deptName='sales', location='东部'}
Department{deptNo=12, deptName='sales', location='西部'}
Department{deptNo=14, deptName='sales', location='北部'}
Department{deptNo=15, deptName='sales', location='东部'}

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