IEG3080 Tutorial 11

1. IEG3080 Tutorial 11 Prepared by Ryan

2. Outline • Enterprise Application Architecture • Layering Structure • Domain Logic • C# Attribute • Aspect Oriented Programming (AOP)

3. Enterprise Application Architecture • Complex systems always break down into layers • e.g. Networking – OSI 7 layers Model • Pros • Working on a single layer without knowing much about other layers • Minimizing dependencies between layers • Con • Transforming from layers harming performance

4. Enterprise Application Architecture • Enterprise Application Architecture – 3-layer • Presentation Layer • Display of information e.g. GUI windows, webpage • Handling user commands • Domain Logic Layer • Business logic (Core) • Data Source Layer • Communication with database, messaging systems

5. Enterprise Application Architecture • Domain Logic Patterns • Domain Model • An object model of the domain that incorporates both behavior and data • Solving the problem in object-oriented way • Pro – Handling complex logic in a well-organized way • Con – “Impedance mismatch” between OO model and relational database

6. Enterprise Application Architecture • O/R Mapping Problems – Identity Problem • OO – Different objects referenced by different pointers • Database – Different rows identified by primary key • Solutions • Identity Field Key Identity Field public class Team { int TeamID; string TeamName; }

7. Team Team ID Team Name Player Player ID Player Name Enterprise Application Architecture • O/R Mapping Problems – Identity Problem • Solutions (Cont’d) • Foreign Key Mapping 1 * Foreign Key Mapping

8. Student Name School University Student Department Secondary Student Class CUHK Student College Enterprise Application Architecture • O/R Mapping Problems – Inheritance How to do mapping?

9. Enterprise Application Architecture • O/R Mapping Problems – Inheritance • Single Table Inheritance • Wasting space – many null columns • Concrete Table Inheritance • Changing the superclass  altering all the subclasses’ tables

10. Enterprise Application Architecture • O/R Mapping Problems – Inheritance • Class Table Inheritance • Requiring multiple joins to rebuild an object

11. Enterprise Application Architecture • Solutions • OO databases • Not common (relational databases are widely adopted) • Tight coupling with the domain model • Automated O/R mapping tools • Not prefect (may solve 80% of the problems) • Expensive

12. Enterprise Application Architecture • Other Domain Logic Patterns • Transaction Scripts • Organizes business logic by procedures where each procedure handles a single request from the presentation • Server page (php, jsp), CGI scripts • Table Module • A single instance that handles the business logic for all rows in a database table or view • Commonly use in .NET development platform

13. C# Attribute • C# Attribute • Embedding information in C# code • Placed in square brackets [ ], above an Attribute Target (e.g. class, field or method) • Reflection • Querying information at run-time • Dynamically invoking methods [serializable] public class Test { … }

14. C# Attribute • Intrinsic Attribute • Built-in attributes in .NET Common Library Runtime (CLR) • Examples • In your assignment 1 • [assembly: AssemblyVersion(“1.0.0.0”)] • [serializable] • [STAThread]

15. C# Attribute • Custom Attribute Use your custom attribute [MyAttribute("MyClass")] public class Test { [MyAttribute("MyMethod")] public void Print { Console.WriteLine("Test Program"); } } Create your custom attribute // Set what kinds of elements can use this custom attribute [AttributeUsage(AttributeTargets.All)] public class MyAttribute : Attribute { // Define your own attribute string myName; public MyAttribute(string name) { myName = name; } public string Name { get { return myName; } } }

16. C# Attribute • Reflection – Querying information public class MyProgram { public static void Main() { Type type = Type.GetType("Test"); foreach (Attribute attr in type.GetCustomAttributes(false)) { // Retrieve attributes for the class MyAttribute myattr = attr as MyAttribute; if (myattr != null) Console.WriteLine(attr.Name); } foreach(MethodInfo method in type.GetMethods()) { foreach (Attribute attr in method.GetCustomAttributes(false)) { // Retrieve attributes for the method MyAttribute myattr = attr as MyAttribute; if (myattr != null) Console.WriteLine(“Method: {0} with Attribute: {1}”, method, attr.Name); } } } } Output MyClass Method: Void Print() with Attribute: MyMethod

17. C# Attribute • Reflection – Invoking methods public class MyProgram2 { public static void Main() { Type type = Type.GetType("Test"); Object o = Activator.CreateInstance(type); // Create a “type” object MethodInfo mi = type.GetMethod("Print"); mi.Invoke(o, null); // Invoke method - “mi” } } Output Test Program

18. Aspect Oriented Programming • OOP • Breaking down a complex system into modules • Encapsulating responsibilities into different objects • Problems • Some tasks cut across multiple modules (crosscutting concern) • Logging • Authentication • Solution: Aspect Oriented Programming (AOP)

19. Aspect Oriented Programming • AOP in C# Non-AOP Implementation public class Test { public void TestMethod() { Log log = new Log(); log.Print("Enter"); // Log when entering this method Console.WriteLine("Test Method"); log.Print("Leave"); // Log with leaving this method } } AOP Implementation [AttributeUsage(AttributeTargets.Class)] public class LogAttribute : ContextAttribute { // Code Here } public class LogProperty : IContextProperty, IContributeObjectSink { // Code Here } public class LogAspect : IMessageSink { // Code Here } [Log] public class Test : ContextBoundObject { public void TestMethod() { Console.WriteLine("Test Method"); } }

20. Aspect Oriented Programming • How does it work in C# • “ContextAttribute” and “ContextBoundObject” • Intercepting the calls(Interception) Client YourObject Without Interception Intercepted by .NET Transparent Proxy Message Sink Client YourObject With Interception

21. References • Enterprise Application Architecture • M. Fowler, “Patterns of Enterprise Application Architecture”, Addison Wesley • C# Attribute • http://www.oreilly.com/catalog/progcsharp/chapter/ch18.html • Aspect Oriented Programming (AOP) • http://www.codeproject.com/gen/design/aop.asp • http://msdn.microsoft.com/msdnmag/issues/02/03/AOP/