Processing in the OrderBroker Orchestration
This section describes how the OrderBroker orchestration takes orders and prepares them for a process manager. The section begins by discussing the general workings of the orchestration. The next part discusses how the orchestration processes a message. It then highlights how the orchestration uses an atomic transaction to improve performance.
|Because of the length of the length of the OrderBroker code, you may want to read this section with the orchestration open in Microsoft® Visual Studio.|
Why an Order Broker?
The purpose of the OrderBroker orchestration is to preprocess an order and route it to the correct process manager. Pre-processing here consists of producing informational messages for the history database, for the servicing system, and to acknowledge receipt of the order. The OrderBroker also creates a generic order message from the customer service request. This normalization of the order allows for generic consumption of the order by elements of the business process.
The order message is a multipart message with routing information separated from the order information. The routing information is also generic and designed to be consumed by any order manager. This, in turn, makes it easier to expand the solution. For information about multi-part messages, see How to Use Multi-part Message Types.
Isolating the brokering function also allows you to move it to another BizTalk group. Because the OrderBroker publishes to the MessageBox database—that is, it is direct-bound—also makes it easier to put the broker in another group --you can move the broker without changing the orchestration. For more information about putting the OrderBroker in another group, see Communication between OrderBroker and OrderManager.
|The OrderBroker orchestration, because it has only one OrderManager to communicate with, simply assigns a constant string to the OrderMgrType field in the order manager message. Typically, in an application where there were multiple order managers, the application would use the Business Rule Engine to determine the proper value for this field and the order routing. For more information about the Business Rule Engine, see Creating and Using Business Rules.|
The OrderBroker orchestration begins with two Receive shapes within a Listen shape. One Receive shape takes messages from the customer support system; the other, messages from the vendor system. Messages from either source have the same schema.
The orchestration extracts the return address from the message and uses it to set the address for the dynamic port, CSRPort. The orchestration uses this port to send acknowledgement and error messages.
The next steps in the OrderBroker orchestration create the history message, the service message, the confirmation message, and the order message to send to the OrderManager orchestration. The orchestration uses the InsertOrderBody utility function to add the order message to the history message.
|In some situations the solution may produce messages that are delivered but not consumed. The order broker orchestration uses a send port to insert information in the history database. This send port uses delivery notification. Configuration maps the send port to a send port group containing two ports—one port for the test configuration (HistoryInsert-Test-SP), one for the regular configuration (HistoryInsert-SP). If you leave both ports in the group running, the solution sends messages on both ports. It thus requests two delivery notifications but processes only one. To avoid this situation, unenlist the test port (HistoryInsert-Test-SP), or stop the test version of the application, BTSScn.BPM.OrderBrokerApp.Test. For more information about delivery notifications, see Using Acknowledgments.|
When constructing the message to send to the OrderManager orchestration, the OrderBroker orchestration creates a multi-part message with two parts. One part contains the routing information; the other, the order itself. The routing part of the message, OrderMgrMsg.Routing, uses a schema defined by a C# class in the SchemaClasses assembly. The broker treats the order part of the message as a generic, or type-agnostic, XML document (System.Xml.XmlDocument) and assigns it to OrderMgrMsg.Order.
There are two fields in the routing information that are especially important to the order manager, OrderMgrMsg.Routing.OrderMgrType and OrderMgrMsg.Routing.Status. The broker sets the OrderMgrType to the type of the order manager that is to handle the order. In the solution, there is only one order manager and the field is set to CABLEORDER. The broker also sets the Status field to ACCEPTED. This is the value that tells the order manager the message is a new order. The order manager in the solution, OrderManager orchestration, uses a Receive shape that filters for the order type equal to CABLEORDER and status equal to ACCEPTED.
The remaining steps in the OrderBroker orchestration send the different messages to the appropriate ports.
Improving Performance with Nested Scopes
One of the noticeable things about the OrderBroker orchestration is its use of nested scopes. The nested scopes are there, in part, to improve performance by limiting the persistence points.
The orchestration engine periodically saves the state of the entire orchestration at execution points called persistence points. The orchestration engine automatically treats several orchestration shapes, including Send shapes, as persistence points. For a list of persistence points and more information about them, see Persistence and the Orchestration Engine.
With five Send shapes, the OrderBroker orchestration should have five persistence points. However, when you group Send shapes inside an atomic transaction scope, the engine recognizes it only needs one persistence point for the scope. Because four of the Send shapes in OrderBroker orchestration are not part of exception handlers and nothing needs to be done after the send, they can go in an atomic transaction scope. This reduces the number of persistence points. For more information about atomic transactions, see Atomic Transactions.
In addition, the orchestration engine will use a single persistence point for nested transactions if the transactions all end at the same time. Thus, the way OrderBroker orchestration nests transactions further reduces the persistence points: the orchestration has a single persistence point due to the use of Scope shapes.
|You can improve performance by minimizing the number of persistence points in an orchestration. You can group Send shapes in an atomic transaction to produce a single persistence point for all of the Send shapes. Ending nested transaction scopes at the same time produces a single persistence point for the transactions.|
An atomic transaction scope cannot have an exception handler. Because of this, the orchestration nests the atomic scope inside a long running transaction. This outer transaction can have an exception handler and it is this handler that processes an exception from the Send shapes.
|Nesting an atomic transaction inside a long running transaction is a common pattern to allow for exception handling.|
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