c＃Linq数据网格视图列检查是否为空

Question

I need check if the value in GridView is null or empty using System.Linq and DataSet .

I have tried this code without success because the error is :

Specified cast is not valid.

How to do resolve this?

My code below.

Thank you in advance or any help.

gv.Columns[4].FooterText = ds.Tables[0].AsEnumerable()
.Select(x => x.Field<Int32>("Tot1")).Where(x => x != null).Sum().ToString();

SQL Query:

sql = " SELECT IFNULL(Tot1,0) AS Tot1
sql += " FROM ";
sql += "    doTable; ";

+------+
| Tot1 |
+------+
|  0   |
|  0   |
|  1   |
|  0   |
|  2   |
+------+

Answer 1

You have to use long for your casting, as IFNULL return BIGINT from MySQL.

gv.Columns[4].FooterText = ds.Tables[0].AsEnumerable()
.Select(x => x.Field<long?>("Tot1")).Where(x => x != null).Sum().ToString();

A nicer version would be:

gv.Columns[4].FooterText = ds.Tables[0].AsEnumerable()
.Select(x => x.Field<long?>("Tot1") ?? 0).Sum().ToString();