TransactionFlowOption有三个选项：

　　一为NotAllowed，这代表了禁止客户端传播事务流到服务端，即使客户端启动了事务，该事务也会被忽略;

　　二为Allowed，这代表允许客户端的事务传播到服务端，但服务器端不一定会引用到此事务;

　　三为Mandatory，这代表服务端与客户端必须同时启动事务流，否则就会抛出InvalidOperationException异常。

[ServiceContract(SessionMode=SessionMode.Required)]
  public interface IOrdersService
  {
    [OperationContract]
    [TransactionFlow(TransactionFlowOption.Mandatory)]
    string PlaceOrder(Order order);
  }

[ServiceBehavior(InstanceContextMode=InstanceContextMode.PerSession, TransactionAutoCompleteOnSessionClose=true)]
  public class OrdersService : IOrdersService
    [OperationBehavior(TransactionScopeRequired=true,
      TransactionAutoComplete=false)]
    public string PlaceOrder(Order order)
    {
      using (var conn = new SqlConnection(connString))
      {
        var cmd = new SqlCommand("Insert Orders (CustomerId) Values( @customerId)", conn);
        cmd.Parameters.Add(new SqlParameter("@customerId", order.CustomerId));

try
        {
          conn.Open();
          if (cmd.ExecuteNonQuery() <= 0)
          {
            return "The order was not placed";
          }

cmd = new SqlCommand("Select Max(OrderId) From Orders Where CustomerId = @customerId", conn);
          cmd.Parameters.Add(new SqlParameter("@customerId", order.CustomerId));

using (SqlDataReader reader = cmd.ExecuteReader())
          {
            while (reader.Read())
            {
              orderId = Convert.ToInt32(reader[0].ToString());
            }
          }
          return string.Format("Order {0} was placed", orderId);
        }
        catch (Exception ex)
        {
          throw new FaultException(ex.Message);
        }
      }
    }

[OperationBehavior(TransactionScopeRequired = true,
      TransactionAutoComplete = false)]
    public string AdjustInventory(int productId, int quantity)
    {
      using (var conn = new SqlConnection(connString))
      {
        var cmd = new SqlCommand("Update Products Set OnHand = 1 Where ProductId = @productId", conn);
        cmd.Parameters.Add(new SqlParameter("@quantity", quantity));

try
        {
          conn.Open();
          if (cmd.ExecuteNonQuery() <= 0)
          {
            return "The inventory was not updated";
          }
          else
          {
            return "The inventory was updated";
          }
        }
        catch (Exception ex)
        {
          throw new FaultException(ex.Message);
        }
      }
    }

----------------------client---------------------------
      using (var tranScope = new TransactionScope())
      {
        proxy = new OrdersServiceClient("WSHttpBinding_IOrdersService");
        {
          try
          {
            result = proxy.PlaceOrder(order);

tranScope.Commit();
          }
          catch (FaultException faultEx)
          {
          }
      }