Order Processing with Policy

This topic applies to Windows Workflow Foundation 4 (WF4).

The Order Processing Policy sample demonstrates some of the key features introduced in the .NET Framework version 3.5 of the Windows Workflow Foundation (WF). The following functionality is new for the WF rules engine:

• Support for operator overloading.

• Support for the new operator, allowing users to create new objects and arrays from WF rules.

• Support for extension methods to make the user experience in calling extension methods from WF rules compatible with C# coding styles.

The sample demonstrates an OrderProcessingPolicy project in which a customer order, which consists of a numbered list of available items and a zip code, is entered. The order is processed successfully if both entries are correct; otherwise, the policy creates error objects, utilizing an overloaded + operator and a predefined extension method to inform the user of the errors.

The sample is comprised of the following projects:

• OrderErrorLibrary

  The OrderErrorLibrary is a class library that defines OrderError and OrderErrorCollection classes. An OrderError instance is created when an invalid input is entered. The library also provides an extension method on the OrderErrorCollection class that outputs the ErrorText property on all OrderError objects in the OrderErrorCollection.

• OrderProcessingPolicy

  The OrderProcessingPolicy project is a WF console application that defines a single PolicyFromFile activity. The activity has the following rules:

  • invalidItemNum

    This rule validates that the item number is between 1 and 6, inclusive. If the item number is within the valid range, the rule does nothing (other than printing to the console). If the item number is not between 1 and 6, the invalidItemNum rule does the following:

    1. Creates a new OrderError object, passing it the item number entered, and sets the ErrorText and CustomerName properties on the object.

    2. Creates an invalidItemNumErrorCollection object.

    3. Adds the newly-created OrderError instance to the invalidItemNumErrorCollection.

    This demonstrates support for the new operator, with which you can instantiate objects inside rules.

  • invalidZip

    This rule validates that the zip code has 5 digits, and is within the range 600 to 99998. If the zip code is within the valid range, the rule does nothing (other than printing to the console). If the length of the zip code is less than 5, or the zip code is not between 00600 and 99998, the invalidZip rule does the following:

    1. Creates an OrderError object, passing it the zip code entered, and sets the ErrorText and CustomerName properties on the object.

    2. Creates an invalidZipCodeErrorCollection object.

    3. Adds the newly-created OrderError instance to the newly-created invalidZipCodeErrorCollection.

    This rule again demonstrates support for the new operator, which allows you to instantiate objects inside rules.

  • displayErrors

    This rule checks to see if there were any errors added by the previous two rules in the two OrderErrorCollection objects invalidItemNumErrorCollection and invalidIZipCodeErrorCollection. If there were errors (either invalidItemNumErrorCollection or invalidZipCodeErrorCollection is not null), the rule does the following:

    1. Calls the overloaded + operator to copy the contents of invalidItemNumErrorCollection and invalidZipCodeErrorCollection to an invalidOrdersCollection OrderErrorCollection instance.

    2. Calls the PrintOrderErrors extension method on invalidOrdersCollection and outputs the ErrorText property on all orderError objects in invalidOrdersCollection.

The overloaded operator + on the OrderErrorCollection is defined in the OrderErrorCollection class, in the OrderErrorLibrary project. It takes two OrderErrorCollection objects and combines them into one OrderErrorCollection object.

The PrintOrderErrors extension method is also defined in the OrderErrorLibrary project. Extension methods are a new C# feature that enables developers to add new methods to the public contract of an existing CLR type, without having to derive a class from it or recompile the original type.

When you run the sample you are prompted to enter a name, the item number of the item to be purchased, and a zip code. This information is then verified by the rules defined in the policy activity. The following is sample output from the program.

Please enter your name: John

What would you like to purchase?
        (1) Vista Ultimate DVD
        (2) Vista Ultimate Upgrade DVD
        (3) Vista Home Premium DVD
        (4) Vista Home Premium Upgrade DVD
        (5) Vista Home Basic DVD
        (6) Vista Home Basic Upgrade DVD

Please enter an item number: 1

Please enter your 5-Digit zip code: 98102

        Executing Rule: invalidItemNum
        Executing Rule: invalidZip
        Executing Rule: displayErrors

                              Thank you for your order, it has been processed.


Workflow Completed
Another Order? (Y/N): y

Please enter your name: Joel

What would you like to purchase?
        (1) Vista Ultimate DVD
        (2) Vista Ultimate Upgrade DVD
        (3) Vista Home Premium DVD
        (4) Vista Home Premium Upgrade DVD
        (5) Vista Home Basic DVD
        (6) Vista Home Basic Upgrade DVD

Please enter an item number: 8

Please enter your 5-Digit zip code: 0000

        Executing Rule: invalidItemNum
        Executing Rule: invalidZip
        Executing Rule: displayErrors

                              Your order contains the following error(s)


Error: No item number found. Please choose an available item.
Error: Invalid zip code. Please choose a zip code between 00600 and 99998.

Workflow Completed
Another Order? (Y/N): n

To set up, build, and run the sample

1. Open the OrderProcessingPolicy.sln project file in Visual Studio 2010.

2. There are two different projects in the solution: OrderErrorLibrary and OrderProcessingPolicy. The OrderProcessingPolicy project uses classes and methods defined in the OrderErrorLibrary.

3. Build all projects.

4. Click Run.

Note:

The samples may already be installed on your computer. Check for the following (default) directory before continuing: <InstallDrive>:\WF_WCF_Samples If this directory does not exist, go to Windows Communication Foundation (WCF) and Windows Workflow Foundation (WF) Samples for .NET Framework 4 to download all Windows Communication Foundation (WCF) and WF samples. This sample is located in the following directory: <InstallDrive>:\WF_WCF_Samples\WF\Basic\Rules\Policy\OrderProcessingPolicy