Terminology and Buzzwords The Policy Injection Application Block what it does, how it works Configuring Policies Using Attributes Extending the Block custom Handlers and Matching Rules

1. Policy Injection in ASP.NET using Enterprise Library 3.0 Alex Homer [email_address] http://www.daveandal.net

4. What are Crosscutting Concerns? Core Concerns Application Business Object Business Object Data Access Object Application Business Object Data Access Object Validation Logging Exception Handling Caching Authorization Crosscutting Concerns Performance Counters

10. Configuring Policies Demo Demo

11. Demo Business Object Members Public members exposed by the two business objects Member Attributed Customer Model Interface Customer Model Notes GetCustomerList()   GetCustomerName(customerID)   GetCustomerNameWithWildcard (customerID)   Uses GetCustomerName method with a wildcard. GetCustomerDetails(customerID)   Not defined in interface. GetCityList(minimumCount)   CityCount   Property. Uses GetCityList

12. Demo Policies The policies defined in the example application Policy Name Matching Rules Call Handlers InterfaceModelPolicy Member Name = GetCustomerNameWithWildcard or GetCustomerList Type Name = InterfaceCustomerModel Logging Handler with Categories = "AuditFile" and "EventLog" Caching Handler with cache duration 20 seconds Exception Handler with Exception Policy = "CustomerModelPolicy” AttributeModelPolicy Method Signature, Name = * and parameter = System.String Type Name = AttributedCustomerModel Logging Handler with Categories = "AuditFile" CacheByTagPolicy Tag Attribute = "ApplyTenSecondCaching" Caching Handler with cache duration 10 seconds

16. Using Attributes Demo Demo

17. Factory Proxy Handlers Matching Rules Pipeline

21. Handler Process Overview public class ExampleHandler : ICallHandler { public IMethodReturn Invoke(IMethodInvocation input , GetNextHandlerDelegate getNext ) { // Perform any pre-processing tasks required in the custom handler. ... // Invoke next handler that the block should execute. This code gets the current return message that you must pass back to the caller: IMethodReturn msg = getNext()(input, getNext); ... // Perform any post-processing tasks required in the custom handler. // You can modify the return message if required. // Return the message to the previous handler or the client. return msg; }

22. Messages and Short-Circuiting Each handler invokes the next one, passing the invocation message along the pipeline and the return message back again A handler can instead simply refuse to call the next handler, and can add information (e.g. an exception) to the return message. Note that previous handlers still execute

23. Short-Circuiting Execution public IMethodReturn Invoke(IMethodInvocation input , GetNextHandlerDelegate getNext ) { GregorianCalendar cal = new GregorianCalendar(); DayOfWeek weekDay = cal.GetDayOfWeek(DateTime.Now); if (weekDay == DayOfWeek.Saturday || weekDay == DayOfWeek.Sunday) { // create an Exception to return and the return message. Exception ex = new Exception("Available on weekdays only"); IMethodReturn msg = input.CreateExceptionMethodReturn(ex) return msg; } else { return getNext()(input, getNext); // invoke the next handler }

24. Custom Handler Attributes [AttributeUsage(AttributeTargets.Class | AttributeTargets.Property | AttributeTargets.Method)] public class CachingCallHandlerAttribute : HandlerAttribute { private TimeSpan expirationTime; public CachingCallHandlerAttribute(int hours , int minutes , int seconds ) { // constructor, save the parameter values expirationTime = new TimeSpan(hours, minutes, seconds); } public override ICallHandler CreateHandler() { // create the appropriate handler instance and return it return new CachingCallHandler(expirationTime); } }