IEG3080 Tutorial 11 Prepared by Ryan

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

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

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

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

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 Team IDTeam Name public class Team { int TeamID; string TeamName; } Key Identity Field

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

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

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 NameSchoolClassDepartmentCollege NameSchoolClass NameSchoolDepartment NameSchoolDepartmentCollege

Enterprise Application Architecture O/R Mapping Problems – Inheritance Class Table Inheritance Requiring multiple joins to rebuild an object NameSchool Class Department College

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

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

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 { … }

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

C# Attribute Custom Attribute 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; } } Use your custom attribute [MyAttribute("MyClass")] public class Test { [MyAttribute("MyMethod")] public void Print { Console.WriteLine("Test Program"); }

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

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

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)

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"); }

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

References Enterprise Application Architecture M. Fowler, “Patterns of Enterprise Application Architecture”, Addison Wesley C# Attribute /ch18.html /ch18.html Aspect Oriented Programming (AOP) /AOP/ /AOP/