I have a DataTable called dtMondayNewsLetter and when the DT returns no rows. i.e. Empty
it shows an error Object reference not set to an instance of an object
CODE
CurrentDirection = Convert.ToString((from DataRow dr in dtMondayNewsLetter.Rows
where (int)dr["PostID"] == PostID select (string)dr["Direction"])
.FirstOrDefault()).Trim();
What changes I need to do in above code to eliminate the error.
As you mentioned, query
from DataRow dr in dtMondayNewsLetter.Rows
where (int)dr["PostID"] == PostID
select (string)dr["Direction"]
returns no rows, so FirstOrDefault() returns null.
so you can do a simply if to check wheter result is available..
var resultString = (from DataRow dr in dtMondayNewsLetter.Rows
where (int)dr["PostID"] == PostID
select (string)dr["Direction"])
.FirstOrDefault();
if (resultString != null)
{
CurrentDirection = resultString.Trim();
}
else
{
//case, when no rows
}
To expand on my comment, I would do something like:
foreach (DataRow dr in dtMondayNewsLetter.Rows)
{
if (dr["PostID"] != DBNull.Value && dr["Direction"] != DBNull.Value)
{
if ((int)dr["PostID"] == PostID)
{
CurrentDirection = dr["Direction"].ToString();
}
}
}
Trying to be concise by shoving everything into a LINQ statement is not always optimal. In your case, there could be a number of objects, or data, which is NULL, thus causing the null reference exception exception.
Inside a one line LINQ statement, it's very difficult to figure out where the NULL object is. Splitting that LINQ statement into a for...each loop makes things a lot easier, and achieves the exact same result.
However, if "PostID" and "Direction" are non-nullable (thus no need to use DBNull.Value checks), then use @nopeflow answer, as that is much safer then your current implementation.
You can use Null-Coalescing Operator. in case that FirstOrDefault returns null return empty string.
CurrentDirection =
Convert.ToString(
(from DataRow dr in dtMondayNewsLetter.Rows
where (int) dr["PostID"] == PostID
select (string) dr["Direction"]).FirstOrDefault() ?? "").Trim();
