C# 4 and .NET 4

OC112 ❘ ChaPTer 51 enterprise services
created by the caller and OrderData uses the same transaction, or a new transaction is created. Here a new
transaction is created because the calling component OrderControl doesn’t have a transaction.
With serviced components, you can use only default constructors. However, you can use the Component
Services Explorer to configure a construction string that is sent to a component (see Figure 51-9). Selecting
the Activation tab of the component configuration enables you to change the constructor string. The option
“Enable object construction” is turned on when the attribute ConstructionEnabled is set, as it is with
the class OrderData. The Default property of the ConstructionEnabled attribute defines the default
connection string shown in the Activation settings after registration of the assembly. Setting this attribute
also requires you to overload the method Construct() from the base class ServicedComponent. This
method is called by the COM+ runtime at object instantiation, and the construction string is passed as an
argument. The construction string is set to the variable connectionString, which is used later to connect
to the database:
[Transaction(TransactionOption.Required)]
[EventTrackingEnabled(true)]
[ConstructionEnabled
(true, Default="server=(local);database=northwind;trusted_connection=true")]
[ComVisible(true)]
public class OrderData: ServicedComponent, IOrderUpdate
{
private string connectionString;
protected override void Construct(string s)
{
connectionString = s;
}
The method Insert() is at the heart of the component.
Here, you use ADO.NET to write the Order object to
the database. (ADO.NET is discussed in more detail in
Chapter 30, “Core ADO.NET.”) In this example, you create
a SqlConnection object where the connection string that
was set with the Construct() method is used to initialize
the object.
The attribute AutoComplete is applied to the method to use
automatic transaction handling as discussed earlier:
[AutoComplete()]
public void Insert(Order order)
{
var connection = new SqlConnection(
connectionString);
The method connection.CreateCommand() creates a
SqlCommand object where the CommandText property is
set to a SQL INSERT statement to add a new record to the
Orders table. The method ExecuteNonQuery() executes
the SQL statement:
figure 51-9
try
{
var command = connection.CreateCommand();
command.CommandText = "INSERT INTO Orders (CustomerId," +
"OrderDate, ShipAddress, ShipCity, ShipCountry)" +
"VALUES(@CustomerId, @OrderDate, @ShipAddress, @ShipCity, " +
"@ShipCountry)";
command.Parameters.AddWithValue("@CustomerId", order.CustomerId);
command.Parameters.AddWithValue("@OrderDate", order.OrderDate);
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