Template Method Pattern

• Gang of Four Gi behavioral pattern
• hLb †Kvb GKwU algorithm Gi skeleton define Kiv nq hvnvi KwZcq steps subclasses ‡_‡K deferred nq ZLb Template Method e¨envi K‡i  subclass algorithm Gi step mg~n redefine Kiv nq (algorithm’s structure cwieZ©b bv K‡i) i.e. Base Class Gi algorithm skeleton Gi KwZcq steps subclasses ‡_‡K deferred nq Ges Template Method e¨envi K‡i subclass algorithm Gi step mg~n algorithm’s structure cwieZ©b bv K‡i redefine Kiv nq|

Intent:

• Base Class Gi algorithm skeleton Gi KwZcq steps subclasses ‡_‡K deferred nq Ges Template Method e¨envi K‡i subclass algorithm Gi step mg~n algorithm’s structure cwieZ©b bv K‡i redefine Kiv nq|

UML Diagram:

• wb‡¤œ Template pattern Gi UML representation Kiv n‡jvt

 

 

• Dc‡ii diagramwU Template pattern define K‡i|
• Dc‡ii diagramwUi class mg~‡ni role wb¤œiƒct-
• AbstractClass abstract steps Gi mv‡_ AbstractClass skeleton process workflow define K‡i| Bnv ConcreteClassA Ges ConcreteClassB ‡K override I implement K‡i|
• Bnv structure  wVK †i‡L subclass Gi Dci  depend K‡I algorithm details altering enable K‡i |
• ConcreteClassA Ges ConcreteClassB AbstractClass ‡_‡K inherit nq, abstract method mg~n implement K‡i Ges algorithm detail hold K‡i|

  Real Life Example:

·         g‡bKwi Home builder company Zv‡`i GKwU building Gi A‡bK¸‡jv subdivision Ki‡e|

·         Subdivision Gi  ‡ÿ‡Î floor plan n‡jv skeleton. Bnv fixed _vK‡e  i.e. cÖwZwU subdivision Gi mgmsL¨vK floor _vK‡e wKš‘ cÖwZwU subdivision Gi floor construction i.e. floor decoration different n‡e| D`vnib ¯^i~c †Kvb subdivision G nq‡Zv Fireplace _vK‡e..

·         Template Method  Gi †ÿ‡ÎI cÖ_‡g GKwU algorithm Gi skeleton define Kiv nq Ges †mB Abyhvqx subclass mg~n define Kiv nq Ges †ÿÎwe‡k‡l subclass mg~‡ni KwZcq step defer K‡i|

Code Example

• GB example G GKwU e-commerce site Gi order return system Gi Dci Template pattern apply Ki‡ev|
• cÖwZwU order return G returning process Gi Dci wfwË K‡i wewfbœ ai‡bi series of process m¤úbœ nq|
• GLv‡b `ywU Kvi‡b order return nq-
• No quibbles return
• Faulty order return
• No  quibbles return G goods Gi price ‡_‡K original post and packaging price deduct(minus) Kiv nq Ges finally product mg~n stock G return nq|
• Faulty return ZLbB nq hLb customer faulty item receive K‡i Ges refund Ki‡Z Pvq| GB‡ÿ‡Î original post and packaging payment Gi mv‡_
• wb‡¤œi wP‡Î exercise Gi mv‡_ involved class mg~n †`Iqv n‡jvt-

• cÖ_‡g GKwU solution create Kwi Ges Dnvi bvg w`B TemplateMethodPattern.
• Then D³ solution G GKwU C# class library project add Kwi Ges Dnvi name w`B TemplateMethodPattern.Model
• Gevi Dnv‡Z GKwU new class add Kwi Ges Dnvi name w`B ReturnAction Ges Dnvi code listing wb¤œiƒc n‡e-

namespace TemplateMethodPattern.Model

{

public enum ReturnAction

{

FaultyReturn = 0,

NoQuibblesReturn = 1

}

}

• GB enumeration Gi gva¨‡g return order Gi type detect Kiv n‡e|
• Then return order entity Gi Rb¨ ReturnOrder.cs bv‡g GKwU class define Ki‡ev hvi definition wb¤œiƒct

namespace TemplateMethodPattern.Model

{

public class ReturnOrder

{

public ReturnAction Action { get; set; }

public string PaymentTransactionId { get; set; }

public decimal PricePaid { get; set; }

public decimal PostageCost { get; set; }

public long ProductId { get; set; }

public decimal AmountToRefund { get; set; }

}

}

• ReturnOrder entity Øviv customer’s order returned n‡q‡Q wK bv Zv represent Kiv nq|
• Action property Øviv return order type determine Kiv nq|
• PaymentTransactionId Øviv order purchase Gi Rb¨ e¨eüZ original payment refer Kiv nq|
• PricePaid  Ges PostageCost Øviv order total Ges shipping costs refer K‡i|
• ProductId Øviv returned product Gi unique identifier hold K‡i|
• AmountToRefund Øviv customer ‡K refunded amount refer K‡i|
• Domain model Øviv abstract template method ‡K specific faulty Ges no quibbles subclass G implement I override Kiv nq|
• Template method create Kivi Rb¨ project G GKwU new class add Kwi Ges Dnvi bvg w`B ReturnProcessTemplate. Bnv GKwU abstract class Ges Bnvi definition wb¤œiƒc n‡e-

namespace TemplateMethodPattern.Model

{

public abstract class ReturnProcessTemplate

{

protected abstract void GenerateReturnTransactionFor(ReturnOrder returnOrder);

protected abstract void CalculateRefundFor(ReturnOrder returnOrder);

public void Process(ReturnOrder returnOrder)

{

GenerateReturnTransactionFor(returnOrder);

CalculateRefundFor(returnOrder);

}

}

}

• Dc‡iv³ code definition অনুযায়ী class এবং প্রথম method দুইটি abstract. সুতরাং ইহাদেরকে subclass এ implement করতে হবে.
• Third method ১ ও ২ নং abstract method call K‡i Ges ReturnOrder entity ‡K argument wnmv‡e pass K‡i|
• GLb Avgiv template method Øq‡K subclass G add Ki‡ev|
• GRb¨ cÖ_‡g Avgiv project G GKwU new class add Ki‡ev Ges Dnvi name w`‡ev NoQuibblesReturnProcess Ges Dnvi code listing wb¤œiƒc n‡e-

namespace TemplateMethodPattern.Model

{

public class NoQuibblesReturnProcess : ReturnProcessTemplate

{

protected override void GenerateReturnTransactionFor(ReturnOrder returnOrder)

{

// Code to put items back into stock...

}

protected override void CalculateRefundFor(ReturnOrder returnOrder)

{

ReturnOrder.AmountToRefund = returnOrder.PricePaid;

}

}

}

• NoQuibblesReturnProcess stock G item mg~n return K‡i| GB logic GenerateReturnTransactionFor method Gi override method G Ae¯_vb K‡i|
• CalculateRefundFor overridden method return order Gi  product  Gi price  G AmountToRefund property set K‡i|
• G‡ÿ‡Î †Kvb postage cost refund nq bv|
• Second subclass I  ReturnProcessTemplate  ‡K inherit K‡i| GB subclass wU Faulty Return Process Gi Rb¨ KvR K‡i| GRb¨ GB subclass  wUi  name n‡e   FaultyReturnProcess class
• g~jZt GB class wU faulty returned item mg~n processing Gi Rb¨ e¨eüZ n‡e|
• FaultyReturnProcess class Gi code wb¤œiƒc n‡e-

namespace TemplateMethodPattern.Model

{

public class FaultyReturnProcess : ReturnProcessTemplate

{

protected override void GenerateReturnTransactionFor(ReturnOrder returnOrder)

{

// Code to send generate order that sends faulty item back to

// manufacturer...

}

protected override void CalculateRefundFor(ReturnOrder returnOrder)

{

ReturnOrder.AmountToRefund = returnOrder.PricePaid +

returnOrder.PostageCost;

}

}

}

• Overridden method i.e.  GenerateReturnTransactionFor method faulty item mg~n refund Kivi Rb¨ e¨eüZ nq|
• CalculateRefundFor method wU NoQuibblesReturnProcess class Gi CalculateRefundFor method Gi logic ‡_‡K differ K‡i i.e. G‡ÿ‡Î c~‡e©v³ class Gi i.e. NoQuibblesReturnProcess Gi CalculateRefundFor method Gi logic Ges eZ©gvb class Gi CalculateRefundFor method Gi logic wfbœZi n‡e|
• Item returning process coordinate Gi Rb¨ Service class create Kivi c~‡e© order  type  Gi Dci base K‡i correct returning process obtain Kivi Rb¨ Avgiv Factory method pattern use Ki‡ev|
• GKwU new class Create Kwi Ges Dnvi name w`B ReturnProcessFactory. G&B class Gi gva¨‡gB Avgiv correct processing object obtain Ki‡Z cvi‡ev| wb‡¤œ GB class Gi details ‡`qv n‡jv-

namespace TemplateMethodPattern.Model

{

public static class ReturnProcessFactory

{

public static ReturnProcessTemplate CreateFrom(ReturnAction returnAction)

{

switch (returnAction)

{

case (ReturnAction.FaultyReturn):

return new FaultyReturnProcess();

case (ReturnAction.NoQuibblesReturn):

return new NoQuibblesReturnProcess();

default:

throw new ApplicationException(

“No Process Template defined for Return Action of “ + returnAction.ToString());

}

}

}

}

• Factory method pattern e¨envi K‡i client end G object creation complexity hide Kiv nq Ges logic mg~n‡K centralize Kiv nq|
• GLb ReturnOrderService class add Ki‡ev  i.e. Item returning process coordinate Kivi Rb¨ Service class add Ki‡ev hvi code wb¤œiƒct

namespace TemplateMethodPattern.Model

{

public class ReturnService

{

public void Process(ReturnOrder returnOrder)

{

ReturnProcessTemplate returnProcess =

ReturnProcessFactory.CreateFrom(returnOrder.Action);

returnProcess.Process(returnOrder);

// Code to refund the money back to the customer...

}

}

}

• Service Gi GKwU simple Process method _v‡K hvnv  ReturnOrder ‡K argument wnmv‡e †bq|
• Service cÖ_‡g factory use K‡i correct ReturnProcessTemplate implementation G obtain K‡i then ReturnOrder entity pass K‡i Ges ReturnProcessTemplate G Process method call K‡i|
• Subclass’s  method use K‡i call item mg~n return K‡i Ges customer receivable amount calculate K‡i|
• hLb series of subclasses Gi code common nq ZLb Template Method pattern use K‡i code centralize Kiv nq|