how can i keep a value which was recorded in database in variable before i updated?

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how can keep a value which it was recorded in database in variable before i updated it? i want the old value for an operation with new value,
example:
NewValue - OldValue = VariableValue
230 - 200 = 30,
by the way the OldValue is NewValue before i updated it.
can u give me an idea about it, if it's possible.

private void ChargerKiloVoitures()
{
			
try {
	_bd.Command.CommandText = "SELECT Kilometrage FROM Voitures " +
	"WHERE NumeroMatricule = \"" + CBNumMatricule.Text + "\"";
	Debug.WriteLine( Environment.NewLine );
	Debug.WriteLine( _bd.Command.CommandText );
	_bd.Reader = _bd.Command.ExecuteReader();
if ( _bd.Reader.Read());
	this.analogCounter2.Number = int.Parse(_bd.Reader["Kilometrage"].ToString());
	this.analogCounter1.Number = this.analogCounter2.Number + VidangeConstant;
					
					
   //i have problem here exactly 
	int OldKilometrage = int.Parse(_bd.Reader["Kilometrage"].ToString());
	int NewKilometrage = int.Parse(_bd.Reader["Kilometrage"].ToString());
	KiloMetrag.Value = NewKilometrage-OldKilometrage;
					
}//if
	_bd.Reader.Close();

}//try
	catch (Exception ex) {
		Debug.WriteLine( Environment.NewLine );
		Debug.WriteLine( ex.Message );
	MessageBox.Show("Une erreur a été détectée : " + Environment.NewLine + ex.Message, "Erreur");
	}//catch

}

Posted 29-Aug-11 8:49am

Atif BOUZAGLAOUI

Updated 29-Aug-11 9:58am

v3

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TheyCallMeMrJames · Answer 1 · 2011-08-29T08:56:00

What do you want to "keep"? You are showing calculations as though you're trying to prove some math operation. Programming languages don't work like that.

You will have a function that accepts the changes, something with a signature like:

private void UpdateDatabase(int myItemID, int newValue)
{
   // this is where you should be updating things
}

At this point, you have the newValue, and before you update the database, you can just fetch a copy of the old value from the database. Use a query to get the value.

From there, you can do whatever math you want to, or log, or whatever turns your crank.

Cheers.

#realJSOP · Answer 2 · 2011-08-29T08:59:00

Solution 2

Save it as a separate variable.

BTW, why are you making your examples backwards from the way it's represented in the code? That does nothing more than confuse people.

Posted 29-Aug-11 8:59am

#realJSOP