动态sql之 foreach 标签

dao接口的形参是 List<简单类型> 这样的:

    List quaryByIds(@Param("idList") List idList);

		
        select * from student
        where 1 = 1
        //注意这个集合判空
            and id in
            
                #{item}
            
        

		

dao接口的形参是 List<对象类型> 这样的:

    List quaryByxObj(@Param("studentList") List studentList);

mapper文件

    
        select * from student
        where 1=1
        
            and id in
            
                #{stu.id}
            
        
    

思路是拼成一个sql的字符串传递给mybatis.

    
    @PostMapping("mybatis/quaryByIds1")
    public List quaryByIds1(@RequestBody List idList){
        StringBuffer sql = new StringBuffer();
        sql.append("select * from student where id in");
        sql.append("(");
        for (Integer id : idList) {
            sql.append(id);//添加id到sql字符串
            sql.append(",");//添加成员之间分隔符
        }
        sql.deleteCharAt(sql.length()-1);//删除最后一个逗号
        sql.append(")");
        return crudService.quaryByIds1(sql);
    }

dao接口

    List quaryByIds1(@Param("sql") StringBuffer sql);

mapper文件

    
        ${sql}