using System;
using System.Data;
using System.Data.SqlClient;
using System.Reflection;
using System.Windows.Forms;
using System.EnterpriseServices;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;

// The following attribute specifies the name of the assembly that holds the component
[assembly: ApplicationName("TransServer")]

// The following attribute specifies where assembly components are loaded on activation
// Library: components run in the creator's process
// Server: components run in a system process, dllhost.exe

[assembly: ApplicationActivation(ActivationOption.Library)]

// AssemblyKeyFile specifies the name of the strong key that isused to sign the assembly.
// The .snk file is generated with sn.exe and is used when building from within VS. .NET

[assembly: AssemblyKeyFile("..\\..\\TransServer.snk")]

namespace TransServer
{

// To host a class in COM+, include the following attributes 
// The transaction attribute enables us to do transactions within this class.
// Requires creates a new transaction if there isn't one present already, The other option is // to take part in the existing transaction.

[Transaction(TransactionOption.Required)] 
public class TransServer : ServicedComponent
{
      private SqlConnection Conn = new SqlConnection ("server=myserver;Trusted_Connection=yes;database=Purchase");

	// Retrieve the current quantity on hand 
	public int GetQtyOnHand(int prodid)
	{
		int qty = 0;
		try
		{			
		Conn.Open();
		SqlCommand Comm = new SqlCommand("select qtyonhand  from product where productid = " + prodid.ToString(), 	Conn);
		SqlDataReader Drdr = Comm.ExecuteReader();
		Drdr.Read();
		qty = (int)Drdr["qtyonhand"];
		Conn.Close();
	}
	catch(Exception e)
	{
		CloseConnOnError();
		MessageBox.Show(e.Message);
	}
	return qty ;
	}
		
	public void CloseConnOnError()
	{
	try
	{
	        Conn.Close();
		}
		catch
		{
		}
	}
		


If the invalid value is used, it throws an COMException so the [AutoComplete()] Attribute automatically does a rollback of the transaction. Note that this sample doesn’t include user defined exceptions which handle COMException. COM Exceptions can also be handled by providing SerializationInfo with the StreamingContext.


[AutoComplete]
public void AutoUpdateQty(int newQty)
{
try
{
	Conn.Open();
	SqlCommand Comm = new SqlCommand(@"
	UPDATE product SET qtyonhand=@currentValue", Conn);
	Comm.Parameters.Add("@currentValue",SqlDbType.Int,4);
	Comm.Parameters["@currentValue"].Value = newQty;
	Comm.ExecuteNonQuery();
}
catch(Exception e)
{
	CloseConnOnError();
	MessageBox.Show(e.Message );
}
	if (newQty<0 || newQty>100)
	{
MessageBox.Show("Aborting the transaction because the new qty (" + newQty + ") is either <0 or >100");
	}
	else
	{
		MessageBox.Show("Committing the transaction");
	}
	try
	{
		Conn.Close();
	}
	catch(Exception e)
	{
		MessageBox.Show(e.Message);
	}
}


This method is similar to the above method except that it tries to update the qty in the database first, then it does validation, if it fails then calls ContextUtil.SetAbort to rollback the transaction.



public void UpdateQty(int newQty)
{
try
{
	Conn.Open();
	SqlCommand Comm = new SqlCommand(@"
	UPDATE product SET qtyonhand=@currentValue", Conn);
	Comm.Parameters.Add("@currentValue",SqlDbType.Int,4);
	Comm.Parameters["@currentValue"].Value = newQty;
	Comm.ExecuteNonQuery();
}
	catch(Exception e)
	{
		CloseConnOnError();
		MessageBox.Show(e.Message );
	}
	if (newQty<0 || newQty>100)
	{
MessageBox.Show("Aborting the transaction because the new qty (" + newQty + ") is either <0 or >100");
	}
	else
	{
		MessageBox.Show("Committing the transaction");
	}
	try
	{
		Conn.Close();
	}
		catch(Exception e)
	{
		MessageBox.Show(e.Message);
	}
	}

		
}
    }



Summary


The next part of the article would deal with developing a User Interface, which uses the above transactional component.