Convert Null db field to string

kallileo

I use this code to read some records from a access database with contacts exported from Outlook. I get an error when the content of a field in the db is NULL bc it cannot be converted to string. How could I correct this and the convert a Null field in a " " string? Thanks static void Main() { Program instan = new Program(); instan.ReadContacts(); Console.Read(); } public void ReadContacts() { try { OleDbDataReader reader = null; OleDbConnection conn = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=c:\\AGH\\epafes_outlook_2007.accdb;Persist Security Info=False"); string comStr = "SELECT FirstName, LastName, BusinessPhone FROM Contacts"; OleDbCommand cmd = new OleDbCommand(comStr, conn); conn.Open(); reader = cmd.ExecuteReader(); int i=1; while (reader.Read()) { string FName = (string)reader["FirstName"]; string LName = (string)reader["LastName"]; string BPhone = (string)reader["BusinessPhone"]; Console.Write("{0,-4}", i); Console.Write("{0,-13}", FName); Console.Write("{0,-13}", LName); Console.Write("{0}", BPhone); Console.WriteLine(); i++; } Console.WriteLine("\nFinish"); conn.Close(); reader.Close(); } catch (Exception e) { Console.Write(e); } }

Colin Angus Mackay

string FName = string.Empty;
object temp = reader["FirstName"];
if (temp != DBNull.Value)
FName = (string)temp;

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Le centriste

kallileo wrote:

string FName = (string)reader["FirstName"]; string LName = (string)reader["LastName"]; string BPhone = (string)reader["BusinessPhone"];

If a column is nullable in the DB, you should check for nullity in your code. Unfortunately, it is not the same as .NET null. You have to do it this way:

if (reader.IsDBNull(reader.GetOrdinal("FirstName"))
{
     FName = null; // Or String.Empty, as you see fit.
}
else
{
     FName = (string)reader["LastName"];
}

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Colin Angus Mackay

Le Centriste wrote:

You have to

"have to" is a bit strong. You don't "have to" do it that way (although it is a reasonable way to check) as there are other reasonable alternatives.

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Le centriste

Yes, you're right. Wrong choice of words. I should have said "Here is an example".

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kallileo

I think I found it....and it seems to work. But I'm not realy sure if this is the right way to do it. string FName = Convert.ToString(reader["FirstName"]); string LName = Convert.ToString(reader["LastName"]); string BPhone = Convert.ToString(reader["BusinessPhone"]); Thanks -- modified at 9:17 Friday 20th July, 2007 This also works: string BPhone = reader["BusinessPhone"].ToString();

Colin Angus Mackay

Curiously, if you look at what Convert.ToString actually does, it just boils down to the same as:

string FName = reader["FirstName"].ToString();

So, is DBNull.Value.ToString() the value that you really want back?

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Lost User

Hi Since string is a reference type you could also do it like this: string FName = reader["FirstName"] as string; string LName = reader["LastName"] as string; string BPhone = reader["BusinessPhone"] as string; greets M@u

kallileo

m@u wrote:

Hi Since string is a reference type you could also do it like this: string FName = reader["FirstName"] as string; string LName = reader["LastName"] as string; string BPhone = reader["BusinessPhone"] as string; greets M@u

Thanks....

Colin Angus Mackay wrote:

Curiously, if you look at what Convert.ToString actually does, it just boils down to the same as: string FName = reader["FirstName"].ToString(); So, is DBNull.Value.ToString() the value that you really want back?

Yes, it is ok to me...

Le centriste

DBNull.Value.ToString() returns an empty string, so it boils down to be the same as the examples we give, I believe.

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