writing audit records of pre and post values

Question

I'm currently using an SqlDataSource in ASP.NET/C# to let users insert, delete and update entries in a table/gridview. Every event needs to be written to an audit table.

I have easily implemented inserting and deleting - when inserting, the main info audited is just the parameter values of the insert query (e.Command.Parameters[0].Value.ToString() etc), and deleting is pretty much the same (just getting the ID in the delete query).

But with updating, I need to log which fields were changed and also their old values. How would I do this? As an example, here is the code for the inserting:

protected void SqlDataSource1_Inserting(object sender, SqlDataSourceCommandEventArgs e)
{
    string fields = e.Command.Parameters[0].Value.ToString() + "," + e.Command.Parameters[1].Value.ToString() + "," + e.Command.Parameters[2].Value.ToString() + "," + e.Command.Parameters[3].Value.ToString() + "," + e.Command.Parameters[4].Value.ToString();
    System.Security.Principal.WindowsPrincipal p = System.Threading.Thread.CurrentPrincipal as System.Security.Principal.WindowsPrincipal;
    string[] namearray = p.Identity.Name.Split('\\');
    string name = namearray[1];
    string queryString = "INSERT INTO Audit (source, action, item, userid, timestamp) VALUES (@source, @action, @item, @userid, @timestamp)";
    using (SqlConnection connection = new SqlConnection("constring - deleted for privacy "))
    {
        SqlCommand command = new SqlCommand(queryString, connection);
        command.Parameters.AddWithValue("@source", "Nominal");
        command.Parameters.AddWithValue("@action", "Insert");
        command.Parameters.AddWithValue("@item", fields);
        command.Parameters.AddWithValue("@userid", name);
        command.Parameters.AddWithValue("@timestamp", DateTime.Now);
        connection.Open();
        try
        {
            command.ExecuteNonQuery();
        }
        catch (Exception x)
        {
            Response.Write(x);
        }
        finally
        {
            connection.Close();
        }
    }

}

How can this be done?

Answer 1

Why not use SQL Triggers?