CSE 136 - Lecture 5 Part 1

C# Classlibrary

Business Objects/Model set of class definitions

Business Logic: if/else, calculations, loops code in the classes

Process/Flow specialized logic

What is Business Logic Layer

service

asp.netjava client

export to xml

presentationdata is diff than

BL data

you willimplement thesein your project

class objects (more on this later - design patterns)

any logics, rules, calculations

validate user input, incoming data, etc.

What is Business Logic Layer 2 Services

exposing business logic to outside system GPA system can provide graduation status for students

Entities Students taking courses. Courses have schedules and location.

Courses are categorized by departments. Rules, Calculations

Students can only register 20 units maximum per quarter CSE136 must be taken after CSE135, etc.

Validation Is the social security # 9 digits? Is credit card all digits?

Cannot rely JavaScript for validation

Business Layer Patterns

Procedure Pattern Transcript Script pattern - A collection of procedures

(steps of execution). Table Module Pattern

similar to transaction script but operations are grouped by data (dataSet/dataTable)

Object-based Pattern Interrelated & Interconnected objects. Active Record Pattern - record looks like data tables

from the database with additional methods() Domain Model Pattern - not ER diagrams, but OOD

diagrams

1980s

1990s

21th century

Procedure Pattern

Map your business components directly onto required user actions.

Best suited for simple scenarios and unlikely changing spec

Simple and no start-up cost Can not handle large/complex specs As complexity grow, becomes more

costly (not easily extended) CSE 136 will NOT use this design pattern

Table Module Pattern

Remember DataSet in DAL (ADO.NET)

Series of transaction grouped by Data

Grouping the info/table by how data are related

Good for quick presentation display

Built-in in ASP.NET

Table Module Pattern 2

What's wrong with this Pattern?

You must wait for SQL stored procedures to finish

If SQL proc changes, it changes the BL structure remove a column changed a column name You can't catch this error

through unit testing

Object-based Pattern - Active Record Pattern Active Record Pattern is based on

DataSet design but create class object for each DataTable.

Duplication and quite a hassle Better than Table Module Pattern

SQL Proc changes won't affect outcome One step closer to Object Oriented

Design, but not object-oriented yet

Object-based pattern - Active Record Pattern ex

// contains a list of students' ID, first name,// last name, birthday.DataSet.Tables["student"];

// Translate DataSet into Active Recordclass Student{ public string id; public string first_name; public string last_name; public DateTime birthday;

}

class StudentCourse{ public string id; public string course_id; public string courseNumber; public string CourseDescription;}

StudentCourse[] student_courses;

DataSet contains aDataTable with

student info andcourses

DataTable withstudent info

becomes a "class"object

DataTable withstudent courses

becomes an arrayof studentCourse

Object-Based Patterns - Domain Model Pattern

Domain Model is also known as Object-Oriented Design

Define the entities and the relationships & flows between them

Each Entity has data (variables) & behavior (methods)

Consider the issues of “coupling” and “cohesion”. “Reuse”, “Maintainability”, and “Extensibility”

A diagram can be really large (divide & conquer) More Object-oriented design using Design Patterns

Compare the Patterns

DataSet &Data Table

Object-oriented

"Enterprise"large systems

Systems are becoming more complex. Not practical anymore

Easier to expand with complexity and rule changes (obamacare)

Domain Model to ER (DAL)

Data Tranfer between BLand DAL

Objects may be recursive (flow chart withboxes & arrows) or a tree-view list (org-chart)

Database storage is not recursive

Mapping the database data to object-oriented& back to db may be difficult but necessary

Class Objects Design - steps

Start with use case diagram Run thru activity diagram to identify

entities and high-level relationship Run thru sequence diagram again to

identify attributes and methods for each entities. You may skip this step for 136 to save time

UML Review 1

private

public

"A" is a class

"A" is an interfaceor abstract class

UML Review 2

A and B call and access each other's elementObject A and B are linked through a class definition

class AlinkB { A a1; B b1; }

Similar to a join-table in database

A has B, and B can outlive ADestroy A, B still exists

A has a pointer to object B

A has a B, and B depends on A.

Destroy A, B also gets destroyed

A instantiated B object

Domain Model – class diagram ex1

Student

IDFirstLastList<Enrollment>

GetGPA()GetCourses()

Grad_Student

GRE_Score

GetUndergradGPA()

Foreign_Student

TOEFL_ScoreCountry

GetForeignGPA()

Enrollment

Course_IDCourse_TitleQuarterYearGrade

Database ER diagram is hidden awayFrom the Domain Model

How many tables to store student info?

Domain Model – class diagram ex2

Customer

IDFirstLastList<Order>List<Review>

GetOrders(param)GetReviews(param)

Order

Order_IDDateList<Order_Item>TotalTaxGrand_TotalList<Payment>

GetOrderItem()CalculateTotal()

Order_Item

Product_IDProduct_NamePriceQty

Payment

Payment_IDCC_NumberAmountReview

Product_IDRatingDate

Review table in the database may have a order_id, but in Domain Model, it is not used.

Domain Model – class diagram ex3

Vehicle

YearMakeModelSubmodelList<Product>

GetMatchingProduct()

Product

IDNameDescriptionVendor_IDVendor_NameList<Inventory>List<BackOrder>

GetInventory()GetBackOrderInfo()

Inventory

Product_IDLocation_IDLocation_NameQuantity

BackOrder

Vendor_IDVendor_NameVendor_AddressQuantity_OrderedDate

Database ER diagram will have more tables to stored these information (vehicle, make, model, vendor, product, location, back_order, etc).

Domain Model – class diagram ex4

DropBox

UserList<Object>List<SharedObject>

GetMyObjects()GetSharedObjects()

User

User_IDNameEmailDate Object

IDNameDate

Folder

List<Object>

File

Size

SharedObjects

User_IDObject_IDAccess_LevelDate

Break Time

CSE 136 - Lecture 5 Part 2

C# Classlibrary

Business Objects/Model set of class definitions

Business Logic: if/else, calculations, loops code in the classes

Process/Flow specialized logic

Why use Design Patterns

Provide a starting point for a solution Speed up productivity in a team Improves system and application design Carpenter: connector design pattern

Object-oriented Design Patterns Creational

The creational patterns aim to separate a system from how its objects are created, composed, and represented

They increase the system’s flexibility in terms of the what, who, how, and when of object creation

Structural Structural patterns are concerned with how classes and

objects are composed to form larger structures Behavioral

Behavioral patterns identify common communication patterns between objects

They increase flexibility in carrying out this communication

Creational Patterns

Factory Singleton Prototype (skip) Abstract Factory (skip) Builder (skip)

Creational - Factory example

<<interface>>ILog

LogToFile LogToDBCreator

+ FactoryMethod(): Log

FactoryMethod(){ if (log_destination == "file") log = new LogToFile() else log = new LogtoDB()

return log}

log_destination isdetermined by aconfiguration file

Client

+ errorLog:ILog

ILog errorlog = Log.FactoryMethod();

Polymorphism

Logging C# exampleavailable on class homepage (136 project)

Creational - Factory

Letting subclasses decide exactly which class to instantiate

Various subclasses might implement the interface

Factory Method instantiates the appropriate subclass based oninformation supplied by the client or extracted from the current state.

<<interface>>IProduct

ProductA ProductBCreator

+ FactoryMethod(): Product

instantiate object

Client

+ product:IProduct

product =creator.FactoryMethod()

Creational - Singleton

Ensure that there is only one instance of a class/program

All requests are directed to that one and only object

The class itself that is responsible for ensuring this constraint,not the clients of the class

Object should not be created until it is actually needed

Creational - Singleton Code

only one instance

C# interview question

Structural Design Patterns

Decorator Proxy Adapter Facade Bridge (skip) Composite (skip) Flyweight (skip)

Structural - Decorator example

The object does not know it is being “decorated” (makes this a useful patternfor evolving systems)

<<interface>>IStudent

+ GPA()

CollegeStudent

+GPA()

InternationalStudent

- ToeflScore- InternationalStudent : IStudent

+ GPA()+ TOEFL()

InternationalStudent objectcontains CollegeStudent

object

Added behavior

CollegeApplication

CollegeStudent doesnot know it is being

extended byInternationalStudent

Structural - Decorator

Open for extension, close for modification

To provide a way of attaching new state and behavior to an object dynamically.

The object does not know it is being “decorated” (makes this a useful patternfor evolving systems)

Decorators both inherit the original class and contain an instantiation of it

<<interface>>IComponent

+Operation()

Component

+Operation()

implements

Decorator

- addedState- Component : IComponent

+ Operation()+ AddedBehavior

inheritancedecorator has a Component

Client

.NET libraries arebased on decoratorpattern

Structural - Proxy example

Web GUI wants to access a service on the business layer to retrieve student info

Web

Student

+ GetStudentInfo()

<<interface>>IStudent

+GetStudentInfo()

Service onbusiness layer

ProxyOnTheWeb

+GetStudentInfo()

add proxy reference

add proxy reference is simple in VS 2010. Right-click and add service reference

Web hasaccess to

Proxy

Proxy hasaccess to

Student object

Routesrequests to theStudent object

Structural - Proxy

Supports objects that control the creation of and access to other objects

Often a small (public) object that stands in for a more complex (private) object

Client

Subject

+ Request()

Proxy

+Request()

<<interface>>ISubject

+Request()Client hasaccess to

Proxy

Proxy hasaccess toSubject

Routesrequests tothe Subject

Structural - Adapter example

Enables a system to use classes whose interfaces don’t quite match its requirements

This pattern promotes programming to Interfaces, not classes.

LazyStudentMainLastYearsCode

+ CalculateGPA()+ Sort()

pre-compiled libraryfrom last year

Adapter

+GetGPA()

inherit

<<interface>>ITarget

+ GetGPA()

implements

GetGPA() invokesCalculateGPA()

LazyStudentMaincalls GetGPA() whichcalls CalculateGPA()

Structural - Adapter

ClientAdaptee

+ SpecificRequest()

Adapter

+Request()

inherit

<<interface>>ITarget

+ Request()

implements

Client callsRequest()

Request() invokesSpecificRequest()

Enables a system to use classes whose interfaces don’t quite match its requirements

This pattern promotes programming to Interfaces, not classes.

Structural - Facade

To provide different high-level views of subsystems whose details are hidden from users

A remote service call from GUI to business layer service is a "remote facade"

Student.CalculateGPA(student_id)

retrieve grades from GPA systemcalculates overall gradescalculate major GPA

Faculty.GetCoursesStats(faculty_id)

retrieve courses taught in the pastcalculate total units taughtcalculate #A's, B's, C's, etc.

Behavioral Pattern

Strategy Chain of Responsibility Iterator (skip - you have seen this in C#

lecture “enumerator”) Skip: Observer, Command, Mediator,

Memento, State, others…

Behavioral - Strategy exampleIf we want to rank students, there may be different ways/algorithms to ranka student.

Rank a student by GPA alone

Rank a student by progress made

Rank a student by research achievements (inventions, breakthroughs)

<<interface>>IRanking

+ Calculate()

RankByGPA

+ Calculate()

RankByGPA.cs

RankByProgress

+ Calculate()

RankByProgress.cs

RankByBreakThru

+ Calculate()

RankByBreakThru.cs

Award

Award has accessto different waysto rank a student

class Award{IRanking rank;

... if (rankby == "GPA") rank = new RankByGPA() else if (rankby = "progress") rank = new RankByProgress() else rank = new RankByBreakThru() result = rank.Calculate()...}

Polymorphism

Behavioral - Strategy

The algorithms can also be expressed independently of the data they are using

Removing an algorithm from its host class and putting it in a separate class

There may be different algorithms (strategies) that are applicable for agiven problem. If the algorithms are all kept in the host, messy code withlots of conditional statements will result

Enables a client to choose which algorithm to use from a family of algorithmsand gives it a simple way to access it

<<interface>>IStrategy

+ Algorithm()

StrategyA

+ Algorithm()

StrategyA.cs

StrategyB

+ Algorithm()

StrategyB.cs

Client

Client has access toboth StrategyA andStrategyB objects

Polymorphism

Client may come From GUI

Behavioral - Chain example

Only get data from server if local cache is missing

Boeing IRAD project

Required high performance. Caching locally.

RAM Local Disk DB on server

<<interface>>IGetData

#successor:GetData

+ Request()

RAM

+ Request()

LocalDisk

+ Request()

CallToServer

+ Request()

GUIClient

data = RAM.Request();

Request(){if (data == null) data = LocalDisk.Request();}

Requst(){if (data == null) data = CallToServer.Request();}

Request(){if (data == null) data = Server.GetData(...);}

Polymorphism

Behavioral - Chain

At the end of the chain, there can be either default or exceptional behavior

A list of Handler objects that have limitations on the nature of the requests they can deal with

If an object cannot handle a request, it passes it on to the next object in the chain

<<interface>>IHandler

#successor:Handler

+ Request()

Handler1

+ Request()

Handler2

+ Request()

successor is thelink to the nextHandler object

CallsSuccessor ifnecessary

Client

A class thatinitiates aRequest

Polymorphism

Review question

Why does domain model a better pattern at the end?

What are the three categories of OO design pattern?

Why are inheritance and polymorphism the center of OO design pattern? Open/close principal, code flexibility.

Demo Code

Business Logic Layer Domain Objects Error Logging implementation (factory

pattern) Data Transfer Object

Your Assignment

Due next Thursday Design and develop business layer based on

UML UML class diagram for Domain Object Model C# Domain Model classes C# Domain Business Logic Must use creational pattern for error-logging (log

to db or file based on app.config) Must use asynchronous call for error-logging Validations (regular expression – cover in day6)

Developing test cases for your business layer

References

.NET : Architecting Applications for the Enterprise

Design Patterns: Elements of Re-usable Object-Oriented Software

C# Design Patterns