Linq循环DataTable,使用匿名对象取出需要的列

var g_id = context.Request["g_id"];
            DataTable dt = new DataTable();
            var sql = @"select a.g_name
                                ,c.cl_name
                                ,c.cl_type
                                ,c.cl_hidden
                                ,c.grid_inner_order
                                ,c.editor
                                ,c.sum_able
                                ,q.f_name
                                ,q.f_type
                                from tbl_grid a 
                                --列
                                left join tbl_grid_column_mapping b 
                                on a.g_id=b.g_id 
                                LEFT JOIN tbl_column c
                                on c.cl_id=b.cl_id
                                --filed
                                left join tbl_column_field_mapping  w 
                                on w.cl_id=b.cl_id
                                left join tbl_field q 
                                on q.f_id= w.f_id
                                where a.g_id='" + g_id+"'";
            try
            {
                dt = dataprovider.FillDataTable(sql, CommandType.Text);
                string grid_name = dt.Rows[0]["g_name"].ToString();
                var column = dt.AsEnumerable().Select(n => new
                {
                    key = n.Field<string>("f_name"),
                    value = n.Field<string>("cl_name")
                }).ToList();
                context.Response.Write("{"g_name": " + grid_name + ","column":" + JsonConvert.SerializeObject(column) + "}");
            }
            catch (Exception e)
            {
                context.Response.Write("失败:" + e.Message);
            }