mybatis学习笔记(8)-动态sql

标签： mybatis

 

 

mybatis核心,对sql语句进行灵活操作，通过表达式进行判断，对sql进行灵活拼接、组装。

if判断

mapper.xml

 
 SELECT * FROM user    AND user.sex=#{userCustom.sex}  AND user.username LIKE '%${userCustom.username}%'


 
 SELECT count(*) FROM user    AND user.sex=#{userCustom.sex}  AND user.username LIKE '%${userCustom.username}%'

测试结果

1.注释掉testFindUserList()方法中的userCustom.setUsername("张三");

//由于这里使用动态sql，如果不设置某个值，条件不会拼接在sql中
userCustom.setSex("1");
//userCustom.setUsername("张三");
userQueryVo.setUserCustom(userCustom);

输出

DEBUG [main] - Checking to see if class com.iot.mybatis.mapper.UserMapper matches criteria [is assignable to Object]
DEBUG [main] - Checking to see if class com.iot.mybatis.mapper.UserMapperTest matches criteria [is assignable to Object]
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 352359770.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@1500955a]
DEBUG [main] - ==>  Preparing: SELECT * FROM user WHERE user.sex=? 
DEBUG [main] - ==> Parameters: 1(String)
DEBUG [main] - <==      Total: 6
[User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市], User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州], User [id=22, username=陈小明, sex=1, birthday=null, address=河南郑州], User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州], User [id=25, username=陈小明, sex=1, birthday=null, address=河南郑州], User [id=28, username=王小军, sex=1, birthday=Tue Feb 23 00:00:00 CST 2016, address=河南郑州]]

可以看到sql语句为reparing: SELECT * FROM user WHERE user.sex=?，没有username的部分

2.userQueryVo设为null,则userCustom为null

//List list = userMapper.findUserList(userQueryVo);
List list = userMapper.findUserList(null);

输出

DEBUG [main] - ==>  Preparing: SELECT * FROM user 
DEBUG [main] - ==> Parameters: 
DEBUG [main] - <==      Total: 9
[User [id=1, username=王五, sex=2, birthday=null, address=null], User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市], User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州], User [id=22, username=陈小明, sex=1, birthday=null, address=河南郑州], User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州], User [id=25, username=陈小明, sex=1, birthday=null, address=河南郑州], User [id=26, username=王五, sex=null, birthday=null, address=null], User [id=27, username=王大军, sex=2, birthday=Tue Feb 23 00:00:00 CST 2016, address=河南郑州], User [id=28, username=王小军, sex=1, birthday=Tue Feb 23 00:00:00 CST 2016, address=河南郑州]]

可以看到sql语句变为了SELECT * FROM user

sql片段(重点)

将上边实现的动态sql判断代码块抽取出来，组成一个sql片段。其它的statement中就可以引用sql片段。

定义sql片段

                       

    
        
            AND user.sex = #{userCustom.sex}
        
        
            AND user.username LIKE '%${userCustom.username}%'
        
    

引用sql片段

                       
 SELECT * FROM user  

foreach标签

向sql传递数组或List，mybatis使用foreach解析

在用户查询列表和查询总数的statement中增加多个id输入查询。两种方法，sql语句如下：

SELECT * FROM USER WHERE id=1 OR id=10 OR id=16
SELECT * FROM USER WHERE id IN(1,10,16)

一个使用OR,一个使用IN

在输入参数类型中添加
List ids 传入多个id

public class UserQueryVo {

    //传入多个id
    private List ids;

    getter、setter方法
    。。。
}

修改mapper.xml

    
                             
    
                             
    
        
        id=#{user_id}
    

    
    
        每个遍历需要拼接的串
        #{user_id}
     -->

测试代码

在testFindUserList中加入

//传入多个id
List ids = new ArrayList();
ids.add(1);
ids.add(10);
ids.add(16);
//将ids通过userQueryVo传入statement中
userQueryVo.setIds(ids);