Leveraging Design Patterns in ABL Applications Phillip Magnay Technical Architect

Leveraging Design Patterns in ABL Applications

Phillip MagnayTechnical Architect

© 2007 Progress Software Corporation2 Leveraging Design Patterns in ABL Applications

Goals of this Session

Many common design problems already have tried and proven solutions

Some wheels have already been invented Design patterns exist in the public domain Design patterns can be readily implemented in

OpenEdge® ABL

What are the take-aways?


Agenda

What are Design Patterns? Origins & Background Benefits Design Pattern Classifications Documenting Design Patterns Implementing Design Patterns in ABL Limitations of Design Patterns

What we’re going to cover…


What are Design Patterns?

Repeatable solution to a software design problem Design “template” Relationships & interactions between classes

and/or objects Situation dependent, must be adapted Not all patterns are “design” patterns

• Architectural pattern

• Code pattern


Origins & Background

Patterns in architecture during the ’70s Programming patterns in the ’80s

Object-Orientation in the ’90s Gang of Four (Gof) in 1994

• Design Patterns: Elements of Reusable Object-Oriented Software

Pattern Languages Pattern Repositories


Benefits

Accelerates the development process Tested & proven approaches Familiar to developers Provides a lexicon, facilitates communication Basis for standards and documentation


Design Pattern Classifications

Creational Patterns Structural Patterns Behavioral Patterns

Fundamental Patterns Meta- Patterns Architectural Patterns


Gang of Four Patterns

Creational Patterns

• Abstract Factory

• Builder

• Factory Method

• Prototype

• Singleton

Structural Patterns

• Adapter• Bridge

• Composite

• Decorator

• Façade

• Flyweight

• Proxy

Behavioral Patterns

• Chain of responsibility

• Command

• Interpreter

• Iterator

• Mediator

• Memento

• Observer

• State

• Strategy

• Template method

• Visitor


Design Pattern Documentation

Pattern Name Classification Also Known As (AKA) Motivation Applicability Structure Participants Collaboration

Consequences Implementation Sample Code Known Uses Related Patterns


Implementing Design Patterns in ABL

Factory Method State Decorator Observer Command


Factory Method Pattern

Name: Factory Method

Classification: Creational

Motivation: Need to define a standard interface to create objects, but allow sub-classes decide which class to instantiate.

Applicability: A class cannot anticipate the class of objects it must create.

Participants: Product, ConcreteProduct, Creator, ConcreteCreator


Factory Method Pattern Structure


Factory Method Pattern Example



CLASS Account:

METHOD PUBLIC VOID Deposit (INPUT amt AS DECIMAL):

/* code */ END METHOD.

METHOD PUBLIC VOID Withdraw (INPUT amt AS DECIMAL):


METHOD PUBLIC VOID PayInterest (INPUT rate AS DECIMAL):


END CLASS.



CLASS PersonalAccount INHERITS Account:

METHOD PUBLIC OVERRIDE VOID Withdraw (INPUT amt AS DECIMAL): /* code */

END METHOD.

METHOD PUBLIC OVERRIDE VOID PayInterest (INPUT rate AS DECIMAL):

/* code */

END METHOD.

END CLASS.



CLASS BusinessAccount INHERITS Account:

METHOD PUBLIC OVERRIDE VOID Deposit (INPUT amt AS DECIMAL):

/* code */

END METHOD.

METHOD PUBLIC OVERRIDE VOID PayInterest (INPUT rate AS DECIMAL):

/* code */

END METHOD.

END CLASS.



CLASS BankBranch:

METHOD PUBLIC Account CreateAccount():

/* code */

END METHOD.

END CLASS.



CLASS RetailBranch INHERITS BankBranch:

METHOD PUBLIC OVERRIDE Account CreateAccount(): DEF VAR rAccount AS CLASS PersonalAccount NO-UNDO. rAccount = NEW PersonalAccount(). RETURN rAccount.

END METHOD.

END CLASS.



CLASS CommercialBranch INHERITS BankBranch:

METHOD PUBLIC OVERRIDE Account CreateAccount(): DEF VAR rAccount AS CLASS BusinessAccount NO-UNDO. rAccount = NEW BusinessAccount(). RETURN rAccount.

END METHOD.

END CLASS.



Main:DO:

DEF VAR rBranch AS CLASS BankBranch NO-UNDO. DEF VAR rAccount AS CLASS Account NO-UNDO.

rBranch = NEW RetailBranch(). rAccount = rBranch:CreateAccount(). rAccount:deposit(1000.00). rAccount:withdraw(500.00). rAccount:payInterest(5.25).

rBranch = NEW CommercialBranch(). rAccount = rBranch:CreateAccount(). rAccount:deposit(1000.00). rAccount:withdraw(500.00). rAccount:payInterest(5.25).

END.


State Pattern

Name: State

Classification: Behavioral

Motivation: Allow an object to alter its behavior at run-time when its internal state changes.

Applicability: An object must change it behavior at run-time depending on its internal state.

Participants: Context, State, ConcreteState subclasses


State Pattern Structure


State Pattern Example



CLASS Account:

DEF PRIVATE VAR rState AS CLASS AccountState NO-UNDO. DEF PUBLIC VAR balance AS DECIMAL NO-UNDO.

CONSTRUCTOR PUBLIC Account (): checkState(). END CONSTRUCTOR.

METHOD PUBLIC VOID Deposit(INPUT amt as DECIMAL): rState:Deposit(amt). checkState(). END METHOD.

METHOD PUBLIC VOID Withdraw(INPUT amt AS DECIMAL): rState:Withdraw(amt). checkState(). END METHOD.

METHOD PUBLIC VOID CalcInterest(): rState:CalcInterest(). checkState(). END METHOD.

…



…

METHOD PRIVATE VOID checkState(): IF balance < 0 THEN DO: IF rState <> ? THEN DELETE OBJECT rState. rState = NEW OverdrawnState(THIS-OBJECT). END. ELSE IF balance >= 0 AND balance < 1000 THEN DO: IF rState <> ? THEN DELETE OBJECT rState. rState = NEW NonInterestState(THIS-OBJECT). END. ELSE DO: IF rState <> ? THEN DELETE OBJECT rState. rState = NEW InterestState(THIS-OBJECT). END. END METHOD. END CLASS.



CLASS AccountState:

DEF PROTECTED VAR rAccount AS CLASS Account NO-UNDO.

CONSTRUCTOR PUBLIC AccountState (INPUT acc AS CLASS Account): rAccount = acc. END CONSTRUCTOR.

METHOD PUBLIC VOID Deposit (INPUT amt AS DECIMAL):

rAccount:balance = rAccount:balance + amt. END METHOD.


rAccount:balance = rAccount:balance - amt. END METHOD.

METHOD PUBLIC VOID CalcInterest(): /* To be overridden */ END METHOD.

END CLASS.



CLASS NonInterestState INHERITS AccountState:

CONSTRUCTOR PUBLIC NonInterestState (INPUT acc AS CLASS Account):

SUPER(acc).

END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID CalcInterest():

/* do nothing, no interest */ END METHOD.

END CLASS.



CLASS InterestState INHERITS AccountState:

CONSTRUCTOR PUBLIC InterestState (INPUT acc AS CLASS Account):

SUPER(acc). END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID CalcInterest():

rAccount:balance = rAccount:balance + (rAccount:balance * 0.0325).

END METHOD.

END CLASS.



CLASS OverdrawnState INHERITS AccountState:

CONSTRUCTOR PUBLIC OverdrawnState (INPUT acc AS CLASS Account):

SUPER(acc). END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID Withdraw (INPUT amt AS DECIMAL): /* overdrawn, do not change balance */ END METHOD. METHOD PUBLIC OVERRIDE VOID CalcInterest():

rAccount:balance = rAccount:balance – (rAccount:balance * 0.1325).

END METHOD.

END CLASS.



Main:DO:

DEF VAR rAccount AS CLASS Account NO-UNDO.

rAccount = NEW Account(). rAccount:CalcInterest().

rAccount:Deposit(500.00). rAccount:CalcInterest().

rAccount:Deposit(600.00). rAccount:CalcInterest(). rAccount:Withdraw(200.00). rAccount:CalcInterest(). rAccount:Withdraw(1000.00). rAccount:CalcInterest().

END.


Decorator Pattern

Name: Decorator

Classification: Structural

Motivation: Attach additional functionality to an object dynamically

Applicability: When extension is required without impacting other classes and subclassing is difficult.

Participants: Component, ConcreteComponent, Decorator,ConcreteDecorator


Decorator Pattern Structure


Decorator Pattern Example



CLASS Account:

DEF PROTECTED PROPERTY balance AS DECIMAL NO-UNDO GET. SET.

CONSTRUCTOR PUBLIC Account():

balance = 0.

END CONSTRUCTOR.


/* to be overridden */ END METHOD.

END CLASS.



CLASS CheckingAccount INHERITS Account:

METHOD PUBLIC OVERRIDE VOID Withdraw (INPUT amt AS DECIMAL ): balance = balance - amt.

END METHOD.

END CLASS.



CLASS AccountDecorator INHERITS Account:

DEF PROTECTED VAR rAccount AS CLASS Account NO-UNDO.

CONSTRUCTOR PUBLIC AccountDecorator (INPUT acc AS CLASS Account):

rAccount = acc.

END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID Withdraw (INPUT amt AS DECIMAL):

rAccount:Withdraw(amt).

END METHOD.

END CLASS.



CLASS AuditedAccount INHERITS AccountDecorator:

CONSTRUCTOR PUBLIC AuditedAccount (INPUT acc AS Account):

SUPER(acc).

END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID Withdraw (INPUT amt AS DECIMAL):

SUPER:Withdraw(amt). AuditWithdrawal(amt).

END METHOD.

METHOD PRIVATE VOID AuditWithdrawal (INPUT amt AS DECIMAL):

/* some auditing code */

END METHOD.

END CLASS.



Main:DO:


DEF VAR rAuditedAccount AS CLASS AuditedAccount NO-UNDO.

rAccount = NEW Account().

rAccount:Withdraw(1000.00).

rAuditedAccount = NEW AuditedAccount(rAccount).

rAuditedAccount:Withdraw(1000.00).

END.


Observer Pattern

Name: Observer


Motivation: Establish a one-to-many relationship between objects so that a state change in one object notifies all related objects.

Applicability: When a state change in one object requires subsequent state changes in several others without knowing the details of the other objects and while avoiding tight-coupling.

Participants: Subject, Observer, ConcreteSubject, ConcreteObserver


Observer Pattern Structure


Observer Pattern Example



CLASS Subject: DEF PROTECTED TEMP-TABLE ttObserver NO-UNDO FIELD observer AS CLASS PROGRESS.Lang.Object.

METHOD PUBLIC VOID Attach (INPUT observer AS CLASS Observer): IF NOT CAN-FIND(ttObserver WHERE ttObserver.observer = observer) THEN DO: CREATE ttObserver. ttObserver.observer = observer. END. END METHOD.

METHOD PUBLIC VOID Detach (INPUT observer AS CLASS Observer): FIND FIRST ttObserver WHERE ttObserver.observer = observer NO-ERROR. IF AVAILABLE ttObserver THEN DELETE ttObserver. END METHOD.

…



…

METHOD PUBLIC VOID Notify(): DEFINE VAR rObserver AS CLASS Observer NO-UNDO. FOR EACH ttObserver: rObserver = CAST(ttObserver.observer, Observer). rObserver:Action(THIS-OBJECT). END. END METHOD.

END CLASS.



CLASS Stock INHERITS Subject:

DEF PUBLIC PROPERTY symbol AS CHAR NO-UNDO GET. SET. DEF PUBLIC PROPERTY price AS DECIMAL NO-UNDO GET . SET (INPUT piPrice AS DECIMAL): price = piPrice. Notify(). END SET.

CONSTRUCTOR PUBLIC Stock (INPUT newSymbol AS CHAR, INPUT newPrice AS DEC):

SUPER (). symbol = newSymbol. price = newprice. END CONSTRUCTOR. END CLASS.



CLASS Observer:

METHOD PUBLIC VOID Action (INPUT subject AS CLASS Subject):

/* to be overridden */

END METHOD.

END CLASS.



CLASS Investor INHERITS Observer:

DEF PRIVATE PROPERTY name AS CHAR NO-UNDO GET. SET.

CONSTRUCTOR PUBLIC Investor (INPUT newName AS CHAR):

name = newName.

END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID Action (INPUT subject AS Subject): DEF VAR rStock AS CLASS Stock NO-UNDO. rStock = CAST (subject,Stock). MESSAGE NAME rStock:price VIEW-AS ALERT-BOX.

END METHOD.

END CLASS.



Main:DO:

DEF VAR rStock AS CLASS Stock NO-UNDO.

DEF VAR rInvestor1 AS CLASS Investor NO-UNDO. DEF VAR rInvestor2 AS CLASS Investor NO-UNDO.

rInvestor1 = NEW Investor("J Johnson"). rInvestor2 = NEW Investor("B Blogs").

rStock = NEW Stock("PRGS", 33.00). rStock:Attach(rInvestor1). rStock:Attach(rInvestor2).

rStock:price = 34.00. rStock:price = 35.00. rStock:DETACH(rInvestor2). rStock:price = 36.00. rStock:Detach(rInvestor1). rStock:price = 29.00. END.


Command Pattern

Name: Command


Motivation: Encapsulate a request as an object enabling the queuing and logging of requests and the un-doing and re-doing of operations.

Applicability: When support for undo and redo is required.

Participants: Command, ConcreteCommand, Client, Invoker, Receiver


Command Pattern Structure


Command Pattern Example



CLASS Account:

DEF VAR rCalculator AS CLASS AccountCalculator NO-UNDO.

DEF PROTECTED TEMP-TABLE ttCommand NO-UNDO FIELD commandNum AS INT FIELD command AS CLASS PROGRESS.Lang.Object INDEX num commandNum.

DEF PRIVATE VAR curr AS INT INIT 0 NO-UNDO.

CONSTRUCTOR PUBLIC Account(): rCalculator = NEW AccountCalculator(). END CONSTRUCTOR. …



… METHOD PUBLIC VOID CalcBalance (INPUT operator AS CHA, INPUT operand AS DECIMAL): DEF VAR rCommand AS CLASS COMMAND NO-UNDO. rCommand = NEW AccountCommand(rCalculator,operator,operand). rCommand:EXECUTE(). CREATE ttCommand. curr = curr + 1. ttCommand.commandNum = curr. ttCommand.command = rCommand.

END.

…



…

METHOD PUBLIC VOID CommandRedo(INPUT levels AS INT):

DEF VAR l AS INT NO-UNDO. DEF VAR lastNum AS INT NO-UNDO. DEF VAR rCommand AS CLASS COMMAND NO-UNDO. FIND LAST ttCommand NO-ERROR. IF AVAILABLE ttCommand THEN lastNum = ttCommand.commandNum. DO l = 1 TO levels: IF curr > lastNum THEN DO: curr = lastNum. LEAVE. END. ELSE

…



…

DO: FIND FIRST ttCommand WHERE ttCommand.commandNum = curr NO-ERROR. IF AVAILABLE ttCommand THEN DO: rCommand = CAST (ttCommand.command, Command). rCommand:Execute(). curr = curr + 1. END. END. END. END METHOD.

END CLASS.



CLASS AccountCalculator:

DEFINE PRIVATE VAR curr AS DECIMAL INIT 0 NO-UNDO.

METHOD PUBLIC VOID Operation (INPUT operator AS CHA, INPUT operand AS DECIMAL):

CASE operator: WHEN '+' THEN curr = curr + operand. WHEN '-' THEN curr = curr - operand. WHEN '*' THEN curr = curr * operand. WHEN '/' THEN curr = curr / operand. END CASE. MESSAGE curr operator operand VIEW-AS ALERT-BOX. END.

END CLASS.



CLASS Command:

METHOD PUBLIC VOID EXECUTE ():


METHOD PUBLIC VOID UnExecute ():


END CLASS.



CLASS AccountCommand INHERITS Command:

DEF PUBLIC VAR accountCalculator AS CLASS AccountCalculator NO-UNDO. DEF PUBLIC PROPERTY operator AS CHAR NO-UNDO GET . SET . DEF PUBLIC PROPERTY operand AS DECIMAL NO-UNDO GET . SET . CONSTRUCTOR PUBLIC AccountCommand (INPUT calc AS CLASS AccountCalculator, INPUT opor AS CHAR, INPUT opand AS DECIMAL ): accountCalculator = calc. operator = opor. operand = opand. END CONSTRUCTOR.

METHOD PUBLIC OVERRIDE VOID EXECUTE():

accountCalculator:Operation (operator,operand). END METHOD.

…



…

METHOD PUBLIC OVERRIDE VOID UnExecute():

DEF VAR undoOperator AS CHAR NO-UNDO. undoOperator = GetUndo(operator). accountCalculator:Operation (undoOperator,operand). END METHOD.

METHOD PRIVATE CHAR GetUndo (INPUT operator AS char): DEF VAR undoOperator AS CHAR NO-UNDO. CASE operator: WHEN '+' THEN undoOperator = '-'. WHEN '-' THEN undoOperator = '+'. WHEN '*' THEN undoOperator = '/'. WHEN '/' THEN undoOperator = '*'. OTHERWISE undoOperator = ' '. END CASE. RETURN undoOperator. END METHOD.

END CLASS.



Main:DO:


rAccount = NEW Account().

rAccount:CalcBalance("+", 100.00). rAccount:CalcBalance("-", 50.00). rAccount:CalcBalance("*", 1.0525). rAccount:CalcBalance("/", 2).

rAccount:CommandUndo(3).

rAccount:CommandRedo(2). END.


Sources of Design Patterns

Gang of Four (GoF) Core J2EE Pattern-Oriented Software Architecture (POSA) Patterns of Enterprise Application Architecture

(Fowler) Microsoft Solution Patterns Enterprise Integration Patterns (Hohpe & Woolf) Microsoft Integration Patterns


Other Relevant Design Patterns

Enterprise Application Patterns• Data Mapper

• Unit of Work

• Lazy Load

• Foreign Key Mapping

• Inheritance Mappers


Limitations of Design Patterns

Not a panacea Not directly reuse-able unlike components Just another set of abstractions Very dependent upon situation & context Don’t always apply to real-world situations More readily implemented in some

programming languages and not others


In Summary

Many common design problems already have tried and proven solutions

Some wheels have already been invented

Design patterns exist in the public domain

Design patterns can be readily implemented in OpenEdge ABL


For More Information, go to…

PSDN• Implementing the OpenEdge Reference Architecture

with Classes• http://

www.psdn.com/library/kbcategory.jspa?categoryID=1212

Progress eLearning Community• What's New OE 10.1 Object Oriented Programming

Documentation• 10.1B Object-oriented Programming manual • 10.1B New and Revised Features manual


Relevant Exchange 2007Sessions

DEV-6: Getting Started with Object-Oriented Programming

DEV-12: Object-Oriented Programming in OpenEdge ABL

DEV-20: Using Classes & Procedures in OpenEdge 10.1B

ARCH-7: A Class-Based Implementation of the OERA


Questions?


Thank you foryour time


Documents

Leveraging Design Patterns in ABL Applications Phillip Magnay Technical Architect