Mybatis——动态SQL环境搭建、if、Choose、set、foreach语句的使用

1.

@SuppressWarnings("all") //抑制警告，全部都不报错

2.随机生成ID

package com.Utils;

import java.util.UUID;

@SuppressWarnings("all") //抑制警告，全部都不报错
public class IDUtils {
    public static String getId()
    {
        return UUID.randomUUID().toString().replaceAll("-","");

    }
}

3.mybatis-config.xml

    
         日志工厂
          使Bean类中的属性与数据库名对应
    

1、接口类

 //if语句查找
    List getblogif(Map map);

2、sql语句 if where

        select * from blog
        
        
            and title=#{title}
        
        
            and author=#{author}
        
        
     
注意 select * from blog where 1=1后面不用加“；”号
 
where只有在有一个子查询的情况下才会加上and或or，否则标签会去掉and或or
 
3、测试类
 
    @Test
    public void getblogif(){
        SqlSession sqlSession=MybatisUtils.getSqlSeesion();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        HashMap map=new HashMap();
        map.put("title","Java");
        List blogs=mapper.getblogif(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }
 
主要是哈希函数的使用
 
三、choose语句 
    
        select * from Blog
        
            
                
                    and title=#{title}
                
                
                    and author=#{author}
                
                
                    and views=#{views}
                

            
        
    
 
 @Test
    public void getblogChoose(){
        SqlSession sqlSession=MybatisUtils.getSqlSeesion();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        HashMap map=new HashMap();
        map.put("title","Java");
        map.put("author","My");
        map.put("views",9999);
        List blogs=mapper.getblogChoose(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }
 
choose仅会执行第一条成功的指令。
 
四、update table set 语句 
    
        update blog
        
            
                title=#{title},      //后面一定要有逗号
            
            
                author=#{author},
            

        
        where id=#{id}  //放在set标签后面
    
 
   @Test
    public void getblogSet(){
        SqlSession sqlSession=MybatisUtils.getSqlSeesion();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        HashMap map=new HashMap();
        map.put("title","Java2");
        map.put("author","My2");
        map.put("id","4fca22d7-70db-4ef3-b04d-ee0d9dfc951d");
        mapper.getblogset(map);
        sqlSession.commit();
        sqlSession.close();
    }
 
如果有逗号，set会自动去除。
 
五、foreach语句 
select * from blog where 1=1 and (id = #{id} or id=#{id})
 
    
        select * from blog
        
            
                id=#{id}
            
        
    

 @Test
    public void getblogForeach(){
        SqlSession sqlSession=MybatisUtils.getSqlSeesion();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        HashMap map=new HashMap();
        ArrayList ids=new ArrayList();
        ids.add(1);
        ids.add(2);
        map.put("ids",ids);
        List blogs = mapper.getForeach(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }