我如何在更新之前保留记录在数据库中的变量值? [英] how can i keep a value which was recorded in database in variable before i updated?

问题描述

在更新变量之前，如何在数据库中保留记录在数据库中的值?我希望将旧值用于具有新值的操作，
例如:
NewValue-OldValue = VariableValue
230-200 = 30，
顺便说一句，在我更新它之前，OldValue是NewValue.
如果可以的话，你能给我一个想法吗?

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

}

推荐答案

您要保留"什么?您正在显示计算，就好像您试图证明一些数学运算一样.编程语言不能那样工作.

您将拥有一个接受更改的函数，该函数带有如下签名:

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
}

此时，您有了newValue，并且在更新数据库之前，您只需从数据库中获取旧值的副本即可.使用查询获取值.

从那里，您可以执行所需的任何数学运算，登录或进行任何曲调操作.

干杯.

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.

将其另存为单独的变量.

顺便说一句，为什么您要从代码中表示的方式向后制作示例?这无非是使人们感到困惑.

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.

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