Comparing textbox value with database field

Here is the algorithm:

1. Read the textbox value
2. Send the value to database, using stored procedure execute the below query to check whether the values exist or not:

declare @itexists as int;

if exists(select * from MyTable where Barcode=@barcode)
    set @itexists=1;
else
    set @itexists=0;

print @itexists;

3. Get the result using ExecuteScalar and perform rest of the operations based on this value


In your case. just modify your database code as below:

public bool CompareBarcode(string barcode)
       {
           using (SqlConnection conn = new SqlConnection(ConnectionSTring))
           {
               SqlCommand cmd = new SqlCommand("uspCheckBarcode", conn);
               cmd .CommandType = CommandType.StoredProcedure;
               cmd.Parameters.AddWithValue("@barcode", barcode);
               return Convert.ToBoolean(cmd.ExecuteScalar());

           }

I am using an SQL Server database.. I created a stored procedure ( SELECT Barcode FROM Equipment WHERE barcode = @barcode)
-when I execute that query and type a registered barcode,it returns it and then when i type an unregistered barcode it doesnt return anything.

>>>Data Access layer

public DataTable CompareBarcode(string barcode)
       {
           using (SqlConnection conn = new SqlConnection(ConnectionSTring))
           {

               DataTable dtBarcode = new DataTable();
               SqlCommand cmd = new SqlCommand("uspCheckBarcode'" + barcode + "'", conn);
               dbAdapter = new SqlDataAdapter(cmd);
               dbAdapter.Fill(dtBarcode);
               return dtBarcode;

           }

>>>Presentation layer

private void txtInputBarcode_TextChanged(object sender, EventArgs e)
       {
           //checks whether barcode entered by user is registered, by checking from the database

               BusinessObject bo = new BusinessObject();
               bo.CompareBarcode(txtInputBarcode.Text);

               //lblBarcodeResult.Text = "Barcode registered";



               //lblBarcodeResult.Text = "Barcode is not registered";

       }

I need an "if" statement that's going to check whether barcode,and return one of the lblresult messages

By doing the compare in the Text change event is not a good idea. rather use something like if text.length = x then run your query. By using the text change event will create a request each time you type a character in the textbox. For a barcode of 13 characters (EAN 13) this will create 13 requests to the database. What does your stored procedure look like.

here is my stored procedure

ALTER PROCEDURE [dbo].[uspCheckBarcode]
@EquipmentBarcode nvarchar (50)
AS
BEGIN
BEGIN TRY
	BEGIN TRANSACTION
	SELECT [Equipment Barcode]
	FROM Equipment
	WHERE [Equipment Barcode]= @EquipmentBarcode
	COMMIT TRANSACTION;
	END TRY
			BEGIN CATCH
			IF @@TRANCOUNT > 0
			BEGIN
				ROLLBACK TRANSACTION
			END
				END CATCH
END