DaraReader problem ...

[nassimnastaran]

Hi ALL ! I want to execute this by OledbDataReader when I want to take ... :

string CalcQuery = @"SELECT SUM(BuyAmount) From SubTblMetal WHERE IDMetal=" + int.Parse(txtId.ToString());
OleDbCommand cmdCacl;
cnnCalc.Open();
cmdCacl = new OleDbCommand(CalcQuery, cnnCalc);
OleDbDataReader dr;
dr = cmdCacl.ExecuteReader();
if (dr.HasRows==false)
{
txtBuyAmount.Text = "0";
throw new Exception();
}
else if (dr.Read())
{
txtBuyAmount.Text = dr[0].ToString();

            }

But when my DataReader has not any row ,I have an error for the value of txtBuAmount.Text please Help , how can get the value of Zero (0) , when dataRow has not any row(value). Thanks a lot !

[PIEBALDconsult]

First off, please use a parameterized query rather than concatenating the value into the statement. Next, don't trust HasRows. Also, why is that throw in there? As you are expecting at most one value, you might do better with ExecuteScalar and then test for DBNull.Value (for when ther are no matching records).

You'll never get very far if all you do is follow instructions.

[DamithSL]

try with

cmdCacl = new OleDbCommand(CalcQuery, cnnCalc);
txtBuyAmount.Text = cmdCacl.ExecuteScalar() as string;

If You Never Try You’ll Never Know

[DamithSL]

Very nicely explained :thumbsup:

If You Never Try You’ll Never Know

[nassimnastaran]

I want To do This :

BuyAmount.Text = "0";

When there is No Row in dataReader thanks

[PIEBALDconsult]

I understand, but are there ever no rows? Or do you get a NULL (DBNull.Value) when there are no matching rows? Even if you do get no rows, it's better to handle that with an else on the other if. You don't need two ifs; you don't need to test HasRows. HasRows is not a member of the IDataReader[^] interface so you can't count on it being in every database system you use (if you ever have to use multiple database system, like I do). Every time I've tried to use HasRows I got burnt.

You'll never get very far if all you do is follow instructions.

[nassimnastaran]

Yes , thanks , I use If and else when dbIsNull . It works .