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 ID Team 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 ID Team ID Player Name

Team ID Team 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

Name School Class Department College

Name School Class

Name School Department

Name School Department College

Enterprise Application Architecture

O/R Mapping Problems – Inheritance Class Table Inheritance

Requiring multiple joins to rebuild an object

Name School

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 al

l rows in a database table or view Commonly use in .NET development platform

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 { … }

C# Attribute

Intrinsic Attribute Built-in attributes in .NET Common Library Runtim

e (CLR) Examples

In your assignment 1 [assembly: AssemblyVersion(“1.0.0.0”)]

[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 informationpublic 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

MyClassMethod: Void Print() with Attribute: MyMethod

C# Attribute

Reflection – Invoking methodspublic 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 object

s 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)

Client YourObject

Client YourObjectTransparent

ProxyMessage

Sink

Without Interception

With Interception

Intercepted by .NET

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/