Hibernate=====HQL实用技术

Posted 2020-10-08 会飞的豆子

Hibernate支持三种查询语言：HQL查询、Criteria查询和原生SQL查询

HQL(hibernate Query Language，hibernate查询语言)是一种面向对象查询语言，其中没有表和字段的概念，只有类、对象和属性的概念

语法：

　　form子句：form +全类名  /   form  +  类名（查询所有）

　　select子句：select  dept.deptname from Dept

　　where子句：from dept where deptName=‘sales‘;

 

HQL执行语句

　　　例子：form子句、select子句、where子句以及参数查询

　　　　建立实体类

　　    

public class Dept {
    private Integer deptno;
    private String dname;

    public Dept() {
    }

    public Dept(Integer deptno, String dname) {
        this.deptno = deptno;
        this.dname = dname;
    }

    public Integer getDeptno() {
        return deptno;
    }

    public void setDeptno(Integer deptno) {
        this.deptno = deptno;
    }

    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }
}

测试方法

package cn;

import cn.happy.entity.Dog;
import cn.hib.entity.Dept;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

/**
 * Created by a on 2017/8/20.
 */
public class Test924 {
    Configuration cfg;
    SessionFactory factory;
    Session session;
    Transaction tx;

    @Before
    public void beforeTest(){
        //创建配置对象
        cfg=new Configuration().configure();
        //根据配置对象创建SessonFactory
        factory=cfg.buildSessionFactory();
        //根据SessionFactory创建Session
        session=factory.getCurrentSession();
        //session=factory.openSession();
        //开启事务
        tx=session.beginTransaction();
    }

    @Test
    public void testlist(){
        String hql="from Dept";
        Query query=session.createQuery(hql);
        List<Dept> list=query.list();
        for (Dept dept : list){
            System.out.println(dept.getDname());
        }
    }
    @Test
    public void selectSomeColumnFromTable(){
        String hql="select dept.deptno,dept.dname from Dept";
        Query query=session.createQuery(hql);
        List<Object[]>list=query.list();
        for(Object[] obj : list){
            for (Object child : obj){
                System.out.println(child);
            }
        }
    }
    @Test
    public void selectSomesColumnFromTable(){
        String hql="select new Dept(dept.deptno,dept.dname) from Dept dept";
        Query query=session.createQuery(hql);
        List<Dept> list=query.list();
        for (Dept dept : list){
            System.out.println(dept.getDname());
        }
    }
    @Test
    public void selectSomeRecordsFromTable(){
        String hql="from dept.deptno,dept.dname from Dept dept where dept.dname=‘RESEARCH‘";
        Query query=session.createQuery(hql);
        List<Dept> list=query.list();
        for (Dept dept : list){
            System.out.println(dept.getDname());
        }
    }

    //案例：参数查询： 方案一：匿名占位符“?”
    @Test
    public void selectByConditionNiming(){
        String hql="from Dept dept where dname=?";
        Query query=session.createQuery(hql);
        query.setParameter(0,"RESEARCH");
        List<Dept> list=query.list();
        for(Dept dept : list){
            System.out.println(dept.getDname());
        }
    }

    //案例：参数查询：方案二：
    @Test
    public void selectByConditionParametername(){
        String hql="from Dept dept where dname=:dname";
        Query query=session.createQuery(hql);
        query.setParameter("dname","RESEARCH");
        List<Dept> list=query.list();
        for(Dept dept : list){
            System.out.println(dept.getDname());
        }
    }
    //案例：参数查询：方案三：name 参数名称绑定++++对象属性
    @Test
    public void selectByConditionParameternameAndObjectAttribute(){
        String hql="from Dept dept where dname=:dname";
        Dept dd=new Dept();
        dd.setDname("RESEARCH");
        Query query=session.createQuery(hql);
        query.setProperties(dd);
        List<Dept> list=query.list();
        for(Dept dept : list){
            System.out.println(dept.getDname());
        }
    }


}