Mybatis动态SQL

什么是动态SQL：

根据不同的条件生成不同的SQL语句
官方文档地址

IF语句

BlogMapper.xml
通过if进行语句的拼接

        select * from mybatis.blog where 1=1
        
            and title =#{title}
        

        
            and author = #{author}
        
    

测试

@Test
    public void queryBlogIfTest(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        HashMap map = new HashMap();
//        map.put("title","Java如此简单");
        map.put("author","狂神说");

        List blogs = mapper.queryBlogIf(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }

        sqlSession.close();
    }

where

上面例子中的mapper.xml变为

 
        select * from mybatis.blog
        
            
                title =#{title}
            

            
                and author = #{author}
            
        
    

测试

    @Test
    public void queryBlogIfTest(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        HashMap map = new HashMap();
//        map.put("title","Java如此简单");
        map.put("author","狂神说");

        List blogs = mapper.queryBlogIf(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }

        sqlSession.close();
    }
}

and被自动去掉
**如果没有给map传入参数

choose、when、otherwise

mapper.xml
有title就按title查，没有title有author就按author查，两者都没有就按views查

         select * from mybatis.blog
         
             

                 
                     title = #{title}
                 

                 
                     and author = #{author}
                 
                 
                    and views = #{views}
                 
             
         
    

测试

    @Test
    public void queryBlogChooseTest(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        HashMap map = new HashMap();
          map.put("title","Java如此简单");
//        map.put("author","狂神说");
          map.put("views",9999);

        List blogs = mapper.queryBlogChoose(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }

        sqlSession.close();
    }

set

mapper.xml

        update mybatis.blog
        
            
                title = #{title},
            
            
                author = #{author}
            
        

        where id = #{id}
    

测试

    @Test
    public void updateTest(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        HashMap map = new HashMap();
          map.put("title","Java如此简单2");
          map.put("author","狂神说");
//          map.put("views",9999);
        map.put("id","7ac18489a06442898f09faf72f5f0bb0");
       mapper.updateBlog(map);


        sqlSession.close();
    }

trim、where、set