Linq结果Int错误：指定的强制转换无效

Question

Below is my code:

   DataTable dt = new DataTable();

    protected void Page_Load(object sender, EventArgs e)
    {

        dt.Columns.Add("RowId");
        dt.Columns.Add("Amount");

        DataRow row = dt.NewRow();
        row[0] = "1";
        row[1] = "2000";

        dt.Rows.Add(row);

        GetRecord(1);
    }

    protected void GetRecord(int RowId)
    {
        var results = from row in dt.AsEnumerable()
        where row.Field<int>("RowId") == RowId
        select row;

        string FetchedRowId = results.ToArray()[0].ToString();
    }
}

When I use this way it gives error: Specified Cast is not valid in line:

where TableRow.Field<int>("RowId") == RowId

But when I convert to:

   protected void GetRecord(int RowId)
    {
        var results = from row in dt.AsEnumerable()
        where row.Field<string>("RowId") == RowId.ToString()
        select row;

        string FetchedRowId = results.ToArray()[0].ToString();
    }

it works. Why row.Field<int> is not working?

Answer 1

The problem is that you didn't specify that your columns are int s. You can specify that with the Add(string, Type) method.

dt.Columns.Add("RowId", typeof(int));
dt.Columns.Add("Amount", typeof(int));

DataRow row = dt.NewRow();
// whether you add strings or ints here doesn't matter, it's converted
row[0] = "1";
row[1] = 2000;