growing object oriented system

Growing Object-Oriented SystemPrinciples, Guidelines, and Methods

Kent WangDec 6, 2012

13年6月6⽇日星期四

Agenda

• Introduction

• Understand The Problem

• Broad-Brush Design

• Implementation

• Recommended Readings


Introduction


Why This Talk


Software Developing Is a Learning Process


Feedback is Critical

Understandthe Problem(Analysis)

Broad-BrushDesign

(Architecture)

Test DrivenDevelopment

(Implementation)

DeployableSystem


Understand the Problem


Understand The Problem

• User Story

• Use Case

• Conceptual Model

• Color Modeling


User Story

Users could pay for their orders from various platform via tenpay


Use Case

UserPay


Use Case Is Valuable But Not The End


Digging A Conceptual Model


Dig Conceptual Model

Payment

Partner

User

PaymentType

Buyer

Seller

PartnerTrade


Color Modeling

Moment-Interval

Role

Description

Party / Place /Thing


User Story Changed

Users could pay for their orders from various platform via tenpay or alipay


Simple Solution

Payment

Partner

User

PaymentType

Buyer

Seller

PartnerTrade


The Missing Concept

Payment

Partner

UserPayment

Type

Buyer

Seller

PartnerTrade

ProviderPayment

PaymentProvider


Models Are Not Right Or Wrong They Are More Or Less Useful


One Team, One Language


Bounded Context

Payment

Partner

PaymentType

ProviderPayment

PaymentProvider


Context Map

ProviderPayment Transaction

unipay tenpayTransaction Map


Get Help If Required


Broad-Brush Design


Broad-Brush Design

• Tackling Complexity

• Architectural Level

• Application Level

• Domain Model Level


Tackling Complexity


Separation of Concerns


Layered Architecture

Application

Presentation

Data Source


Layered Architecture

Application

Presentation

Data Source

Domain


High Level of Abstraction


Architectural Level


Infrastructure

• Distributed or Not

• Synchronous or Asynchronous

• Data Source


Architectural Style

TransactionScript

Table Module

Domain Model

Complexity

Tool-Chain


Location of Domain Logic

DAOAO

Domain

vs.


Concurrent Control

• Transaction is not Silver Bullet

• Optimistic or Pessimistic

• Offline or Not


Application Level


Walking Through Scenarios

User Submit Payment

Save PaymentGet Payment Parameter

Submit To Provider

PresentationLayer

ApplicationLayer


Intension-Revealing Interface

CUnipayAO

GetPaymentParameter

CUnipayAO

ProcessTrade vs.


Do One Thing

CUnipayAO

GetPaymentParameter

Save or update Payments

Assemble Payment Parameters


Command Query Separation

System CommandQuery

State A

State B


Command Query Separation

CUnipayAO

GetPaymentParameter

SetupPaymentSave or update

Payments

Assemble Payment Parameters


Module

Payment

Payment ProviderPartner

Notification HistorySecurity

Settlement


Domain Model Level


Simplify Associations

Payment

Partner

UserPayment

Type

Buyer

Seller

PartnerTrade

ProviderPayment

PaymentProvider



Payment

Partner

PaymentType

PartnerTrade

ProviderPayment

PaymentProvider



Payment

Partner

PaymentType

ProviderPayment

PaymentProvider

1..*



Payment

Partner

PaymentType

ProviderPayment

PaymentProvider

1current


Design Is Not Just A Technical Issue


Integrity Problem

ChargePlan

ChargePlanLineItem

ChargePlanLineItem

amount = 50 amount = 50

amount = 100

ChargePlanLineItem

amount = 50


Aggregate

ChargePlan

ChargePlanLineItem

ChargePlanLineItem

amount = 50 amount = 50

amount = 100

ChargePlanLineItem

amount = 50


Domain Model Pollution

ao_unipay_settle

PaymentRelay Service

ao_unipay

Transaction


Anti-Corruption Layer

ao_unipay_settle nao_unipay_tenpay

Tenpay Service Payment

Relay Service

ao_unipay

Transaction


Design To Test

Tenpay ServiceFacade

Mock Tenpay Relay Client

Tenpay ServiceFacade Test

1. RegisterChargePlan(plan)

3. Execute(request, response)

4. Checking Request5. ReturnResponse

6. Return Response

7. ParseResponse

2. Assemble Request

8. Return Result

9. Checking Result


Implementation


Implementation

• Design Tools

• Make A New Type

• Consistent Abstraction Level

• Open Close Principle

• Extract Hidden Concept


Costly Tools Don’t Produce Better Designs


UML Without CASE


CRC CardCTenpayProviderType

Make Tenpay Trade No

Make Tenpay Settle No

Get Request Builder

CTenpayTradeNo

CTenpayProvider

CTenpayRequestBuilder

Class

Respon

sibility

Collaborator


Duplicated Code// inside NotifyPayment function// inside GetPayment fuction

if (sProviderTradeNo.length() != 28){ return ERR_APP_PARAM_INVALID;}

uint64_t ddwProviderPartnerNo = lexical_cast<uint64_t>(sProviderTradeNo.substr(0, 10))

uint64_t ddwSerialNo = lexical_cast<uint64_t>(sProviderTradeNo.substr(18));

dwRet = GetPaymentByProviderTradeNo( ddwProviderPartnerNo, ddwSerialNo);


Make A New Type

CTenpayTradeNo

Make Tenpay Trade No

Parse Tenpay Trade No

Verify Tenpay Trade No

CTenpayProvider

Get Date From Trade No

Get Serial No FromTrade No


Use The New Type

// inside NotifyPayment function// inside GetPayment fuction

CTenpayTradeNo oTradeNo;if (!CProviderTradeNo::TryParse(sProviderTradeNo, oTradeNo){ return ERR_APP_PARAM_INVALID;}

dwRet = GetPaymentByProviderTradeNo( oTradeNo.GetProviderPartnerNo(), oTradeNo.GetProviderTradeSerialNo());


Too Much Detail// inside SetupPayment function

if (dwRet == ERR_PAYMENT_NOT_FOUND){

CPayment oPayment;oPayment.SetPaymentId(NextPaymentId());oPayment.SetAmount(rTrade.GetAmount());oPayment.SetBuyerUid(rTrade.GetBuyerUid());oPayment.SetSellerUid(rTrade.GetSellerUid());// ... 50 lines more oPayment.SetLastUpdateTime(CTime::Now());

dwRet = m_pDao->SavePayment(oPayment);if (dwRet != 0){ // ... 10 lines of error handling}return dwRet;

}


Code Closer To Problem

// inside SetupPayment function

if (IsPaymentNotExist(dwRet)){ return CreatePayment();}else{ return MakeSurePriceHasNotChanged();}


Keep Consistent Abstraction Level


Feature Envy// inside GetPaymentParameter function

...

if (rProvider.GetType() == TENPAY){ BuildBasicParameter(rPayment); if (rSpec.GetPaymentMethod() == STANDARD) {

BuildParameterOfTenpayStandardPayment(rPayment); } else if (rSpec.GetPaymentMethod() == BANK) { BuildParameterOfTenpayBankPayment(rPayment); }}

...


Power Of ValuesIPaymentRequestBuilder

Build Payment Request

GetPaymentUrlCopyPaymentParameters

CProviderType

CProvider

CTenpayStandardPaymentRequestBuilder


GetPaymentUrl

CopyPaymentParameters

CTenpayProviderType

CTenpayBankPaymentRequestBuilder


GetPaymentUrl

CopyPaymentParameters

CTenpayProviderType


The Clean Way

// inside GetPaymentParameter function

...

IPaymentRequestBuilder* pBuilder = rSpec.GetPaymentMethod().NewPaymentRequestBuilder(rProvider);

pBuilder->Build(rPayment);

...


Open for ExtensionClose for Modification


Extract Hidden Concept

// inside NotifyPayment function

...

if (rPayment.GetCurrentProviderPaymentId() == rProviderPayment.GetProviderPaymentId() &&

rPayment.IsWaitPay()){

rPayment.Accept(rProviderPayment);}

...



Payment ProviderPayment

IPaymentAcceptingPolicy

*



// inside NotifyPayment function

IPaymentAcceptingPolicy* paymentAcceptingPolicy;

...

if (paymentAcceptingPolicy->IsAllowedToAccept( rPayment, rProviderPayment))

{rPayment.Accept(rProviderPayment);

}

...


Making Implicit Concept Explicit


growing object oriented system

Technology