(摘)hibernate hql总结

1. 查询整个映射对象所有字段 

//直接from查询出来的是一个映射对象，即：查询整个映射对象所有字段
        String hql = "from Users";
        Query query = session.createQuery(hql);

        List<Users> users = query.list();
        for(Users user : users){
            System.out.println(user.getName() + " : " + user.getPasswd() + " : " + user.getId());
        }

   
    
输出结果为：     
name1 : password1 : 1    
name2 : password2 : 2    
name3 : password3 : 3    


2.查询单个字段 

//查询单个字段
        String hql = " select name from Users";
        Query query = session.createQuery(hql);

        List<String> list = query.list();
        for(String str : list){
            System.out.println(str);
        }

   
输出结果为：     
name1     
name2     
name3    


3.查询其中几个字段 

//查询其中几个字段
        String hql = " select name,passwd from Users";
        Query query = session.createQuery(hql);
        //默认查询出来的list里存放的是一个Object数组
        List<Object[]> list = query.list();
        for(Object[] object : list){
            String name = (String)object[0];
            String passwd = (String)object[1];

            System.out.println(name + " : " + passwd);
        }

   
输出结果为：     
name1 : password1     
name2 : password2     
name3 : password3    


4.修改默认查询结果(query.list())不以Object[]数组形式返回，以List形式返回 
引用 

//查询其中几个字段,添加new list(),注意list里的l是小写的。也不需要导入包，这样通过query.list()出来的list里存放的不再是默认的Object数组了，而是List集合了
        String hql = " select new list(name,passwd) from Users";
        Query query = session.createQuery(hql);
        //默认查询出来的list里存放的是一个Object数组，但是在这里list里存放的不再是默认的Object数组了，而是List集合了
        List<List> list = query.list();
        for(List user : list){
            String name = (String)user.get(0);
            String passwd = (String)user.get(1);

            System.out.println(name + " : " + passwd);
        }

  
        /**  
        输出结果为：  
         name1 : password1  
        name2 : password2  
        name3 : password3  
         */ 

5.修改默认查询结果(query.list())不以Object[]数组形式返回，以Map形式返回 

//查询其中几个字段,添加new map(),注意map里的m是小写的。也不需要导入包，这样通过query.list()出来的list里存放的不再是默认的Object数组了，而是map集合了
        String hql = " select new map(name,passwd) from Users";
        Query query = session.createQuery(hql);
        //默认查询出来的list里存放的是一个Object数组，但是在这里list里存放的不再是默认的Object数组了，而是Map集合了
        List<Map> list = query.list();
        for(Map user : list){
            //一条记录里所有的字段值都是map里的一个元素,key是字符串0,1,2,3....，value是字段值
            //如果将hql改为：String hql = " select new map(name as username,passwd as password) from Users";,那么key将不是字符串0,1,2...了，而是"username","password"了
            String name = (String)user.get("0");//get("0");是get(key),注意:0,1,2...是字符串，而不是整形
            String passwd = (String)user.get("1");

            System.out.println(name + " : " + passwd);
        }

    
        /**   
        输出结果为：   
         name1 : password1   
        name2 : password2   
        name3 : password3   
         */    

6.修改默认查询结果(query.list())不以Object[]数组形式返回，以Set形式返回,但是因为Set里是不允许有重复的元素，所以:username和password的值不能相同。只需将hql改为：

String hql = " select new set(name,passwd) from Users";

7.修改默认查询结果(query.list())不以Object[]数组形式返回，以自定义类型返回 

自定义类： 

package com.domain;

public class MyUser {

    private String username;
    private String password;
//因为：String hql = " select new  com.domain.MyUser(name,passwd) from Users";所以必须要有接受2个参数的构造函数
    public MyUser(String username,String password){
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }


}

 

//通过query.list()出来的list里存放的不再是默认的Object数组了,而是自定义的类MyUser,必须加包名，String hql = "from Users";中的Users类也是必须加包名的，但是因为再Users.hbm.xml里<hibernate-mapping auto-import="true"> auto-import默认值为true（所以auto-import属性也可以不写）,自动导入了
        String hql = " select new  com.domain.MyUser(name,passwd) from Users";
        Query query = session.createQuery(hql);
        //默认查询出来的list里存放的是一个Object数组，但是在这里list里存放的不再是默认的Object数组了，而是MyUser对象了
        List<MyUser> myUsers = query.list();
        for(MyUser myUser : myUsers){
            String name = myUser.getUsername();
            String passwd = myUser.getPassword();
            System.out.println(name + " : " + passwd);
        }

    
        /**   
        输出结果为：   
        name1 : password1   
        name2 : password2   
        name3 : password3   
         */    


8：条件查询 

//条件查询，参数索引值从0开始，索引位置。通过setString,setParameter设置参数
        String hql = "from Users where name=? and passwd=?";
        Query query = session.createQuery(hql);
        //第1种方式
//      query.setString(0, "name1");
//      query.setString(1, "password1");
        //第2种方式
        query.setParameter(0, "name1",Hibernate.STRING);
        query.setParameter(1, "password1",Hibernate.STRING);
        List<Users> list = query.list();
        for(Users users : list){
            System.out.println(users.getId());
        }

 

//条件查询，自定义索引名(参数名):username,:password.通过setString,setParameter设置参数
        String hql = "from Users where name=:username and passwd=:password";
        Query query = session.createQuery(hql);
        //第1种方式
//      query.setString("username", "name1");
//      query.setString("password", "password1");
        //第2种方式,第3个参数确定类型
        query.setParameter("username", "name1",Hibernate.STRING);
        query.setParameter("password", "password1",Hibernate.STRING);
        List<Users> list = query.list();
        for(Users users : list){
            System.out.println(users.getId());
        }

   

//条件查询,通过setProperties设置参数
        String hql = "from Users where name=:username and passwd=:password";
        Query query = session.createQuery(hql);
        //MyUser类的2个属性必须和:username和:password对应
        MyUser myUser = new MyUser("name1","password1");
        query.setProperties(myUser);
        List<Users> list = query.list();
        for(Users users : list){
            System.out.println(users.getId());
        }

9.多表查询: 

hql = "select new map(a.p2Name as p2Name,a.p2Remark as p2Remark, b.p1Name as p1Name) from Parenttwo a, Parentone b where a.parentone =b";
        query = session.createQuery(hql);
        list = query.list();
        for (Object obj : list) {
            Map map = (Map) obj;
            System.out.println(map.get("p2Name")+","+map.get("p2Remark")+","+map.get("p1Name"));
        }

10. left join ... on 

hql = "select new map(a.p2Name as p2Name,a.p2Remark as p2Remark, b.p1Name as p1Name) from Parenttwo a left join a.parentone b";
hql = "select new map(a.p2Name as p2Name,a.p2Remark as p2Remark, b.p1Name as p1Name) from Parenttwo a left join a.parentone b where a.p2Name='abcd'";