MTAT.03.229 Enterprise System Integration...Hexagonal architecture DDD & DATA ACCESS LUCIANO...

MTAT.03.229Enterprise System IntegrationLecture 2: Domain model and data access layerLucianoGarcía-BañuelosUnivers i tyof Tartu

TheAnatomyofanEnterpriseSystem

1

Enterprisesoftw

are Presentation

Applicationlogic

Dataaccess

Applicationlayers

• Usersinteractwiththesystemthroughapresentationlayer(akauserinterface orUI)

• Theapplicationlogic (akabusiness logic)determineswhatthesystemactuallydoes:◦ Enforcesbusinessrules◦ Coordinatesbusinessprocesses

• Thedataaccesslayer facilitatestheaccesstopersistentdatamanipulatedbytheapplicationlogic.◦ Includesaccesstodatabases,searchengines,documentmanagersand/orafilesystem.

DDD&DATAACCESSLUCIANOGARCÍA-BAÑUELOS

Hexagonalarchitecture

DDD&DATAACCESSLUCIANOGARCÍA-BAÑUELOS 2

Application

Domain model

RESTadapter

SOAPadapter

Mem

JPAadapter

MongoDBadapter

Hash mapadapter

Messagingadapter Messaging

adapterEMail

adapter

Web UIadapter

• Allowsmanydisparateclientstointeractwiththesystem:◦ The DomainmodelisonlyaccessibleviaaninternalApplicationAPI(innerhexagon)

◦ Needanewclient(withdifferent integrationrequirements)? JustaddanAdapter

◦ Usealsoadapterstointegratewithexternalapplicationsandinfrastructureservices

Domain-drivendesign(DDD)• Domain-drivendesign(DDD)isanapproachtodevelopingsoftwarefor complexneeds bydeeplyconnectingtheimplementationtoanevolvingmodelofthecorebusinessconcepts.

• Itspremisesare:◦ A developmentprojectmustprimarilyfocusinthecoredomainanddomainlogic

◦ Themodeliscentraltoanycomplexdesign◦ Thedevelopmentreliesoncreativecollaborationbetween technicalanddomainexperts toiterativelycuteverclosertotheconceptualheartoftheproblem


TheFrameworkofDDD• Ubiquitouslanguage• Strategicdesign◦ BoundedContext◦ ContextMaps◦ Patterns:Sharedkernel,Anti-corruptionlayer,etc.

• Tacticdesign◦ Structuralpatterns:Entities,ValueObjectsandAggregates◦ Lifecyclepatterns:RepositoriesandFactories◦ Behaviorpatterns:Services,Domainevents,Eventsourcing(CQRS)◦ Stylepatterns:Modules,IntentionRevealingInterfaces,Specifications


Ubiquitous language


Sowhenwechangethecustomsclearancepoint,weneedtoredothewholeroutingplan

Right.We’lldeletealltherowsintheshipmenttablewiththecargoid.Then,we’llpasstheorigin,destinationandnewclearance

pointintotheRoutingservice,anditwillrepopulatethetable.Delete therows?OK,

whatever.Anyway,ifwedidn’thaveacustomsclearancepointatall

before,we’llhavetodothesamething.

Alanguagestructuredaroundtheapplication domain• Understoodbydomainexpertsandsoftwaredevelopment team

• Essentialincommunicatinginsightsfromthedomainthatmustbetransferred intothemodel

Strategicdesign• Inordertotacklecomplexity, thedomainisdecomposed insubdomains, usuallybasedonBusinesscapabilities◦ Identifythecoresubdomainandothersupportingsubdomains◦ Characterizetheofrelationshipsbetweensubdomains

• Theusageoftheubiquitous languageusedinthecoredomaindelimitsa bounded context◦ Usetheubiquitouslanguageintheprocessofmodelingthedomain◦ Strivetokeeptheconsistencyofthedomainmodelwiththecode◦ Infact,thecodeitselfisanotherrepresentationofthemodel

• WeneedtoidentifyanddescribethenatureoftherelationshipsbetweenboundedcontextsbymeansofContextMaps◦ Teamsworkingindifferentcontextboundsshouldtakecare(oratleastawareof)potential interdependencies


Rentit’s domain


Plant catalogand purchase

orders

Maintenance plan

Plant reservation

Invoicing

Plant transportation

Domain

Maintenance

Reservations

Transportation

Invoicing

Sales(core)

Sub-domain

BoundedContext

Exercise:Rentit• Sales◦ Queryingtheplantcatalog◦ Creatingapurchaseorder◦ Processingofapurchaseorder◦ Planttransportation◦ Invoicing

• Maintenance◦ Creationofyearlymaintenanceplan◦ Schedulingofmaintenancetasks

• Reservations◦ Howtocoordinaterentalandmaintenance(implicit)


QueryingtheplantcatalogCustomers query Rentit’s plant catalog. For each plant, the plant catalogprovides a name, a description, and a daily rental price. Each entry in theplant catalog is referred to as plant inventory entry.There might be multiple plants for the same entry, each one having adifferent serial number. An actual plant is referred to as a plantinventory item.


CreatingaPurchaseOrderA customer can check a plant's availability for a period of time. If theplant is available, he/she can create a Purchase Order with the followinginformation: customer’s company, contact person (e.g. name, email),construction site’s address, plant inventory entry’s identifier, the startand end dates of the rental period.


ProcessingaPurchaseOrderA PO is initially considered ascreated. A clerk checks thecustomer’s credit status withthe department of finances,and the plant's availability. Ifeverything is OK, the clerknotifies the customer thatthe PO has been acceptedand updates the cost of thePO. Otherwise, the clerknotifies the rejection of thePO with an explanatory note.


Theoverallpicture


0..1

maintPlan

reservation1

0..1

rental

reservation0..1

1 plantreservation

1

1plant

TacticDesign


Modeldrivendesign

ServicesEntities

Valueobjects

Modules

Repositories

Aggregates

Factories

accesswithmaintain

integritywithactasrootofencapsulate

withencapsulate

with

encapsulatewith

encapsulatewith

accesswith

BuildingblocksintheModelEntity ValueObject

Haveidentitythatmustbepreserved all alongtheirlife-cycle

Things withinthemodelthatarenotuniquelyidentified

Distinguishedfromothersimilarobjectsbytheiridentityandnotbasedintheirproperties

A pairofvalueobjectsareequalifthevalueoftheirpropertiesmatch

Theirpropertiesaremutable Are immutable,i.e.replaceratherthanupdate

Involvestructureandbehavior(encapsulatedomainlogic)

Involve alsostructureandsomeadditionalvalidationlogic


Backtoourrunningexample


Aboutassociations:• Mindtraversaldirections• Eliminatenonessential

associations• Uncovercomposition

relations(stronglifecycledependencies)

ClassifytheclassesinyourdomainmodelasEntitiesorValueobjects

☛ Inthefigure,entities areshowningreyandvalueobjectsinblue

Aggregates• Anaggregateisaclusterofentitiesandvalueobjects,treatedasonesingleunit◦ IthasonerootentitythatisknownastheAggregateRoot

◦ Externalobjectsinteractwiththeaggregateonlyviatheaggregateroot

◦ Asaresultoftheabove◦ Anyrequiredchangeonthe internalobjectsisalwaysmediatedbytheaggregateroot!

◦ Theaggregaterootisresponsibleforensuringaggregateinvariants

• Notethatanyentities/valueobjectwithinanaggregatecanrefertootherexternalentities


Aggregates inourrunningexample


reservation1

maintPlan

0..1

0..1

rental

reservation0..1

1 plant

1plant

Moreonaggregates


Repositories• Arepositoryisanabstractionoverthepersistencesupport◦ Providesbasicoperationsforstoring/retrievingobjectsofanaggregate

◦ Promotesacleanseparationbetweendomainandthetechnicalissuesrelatedtopersistencemanagement

◦ Definesaunitofwork◦ Arepositoryisusuallyassociatedwithonesingledatasource◦ Incaseofmultipledatasources,thetransactionboundaryshouldbetheaggregateitself

• Althoughnotarule,wewillprefertouseasinglerepositoryperaggregate◦ Notalwaysappropriate:Howcanwechecktheavailabilityofplants?


Examplerepository


Specificationpattern


expr

1

components

*

Specificationpattern


public List<Invoice> selectSatisfying(InvoiceSpecification spec) {List<Invoice> result = new ArrayList();

for (Invoice invoice: invoiceRepo.findAll())if (spec.isSatisfiedBy(invoice)) result.add(invoice);

return result;}

invoices = invoiceRepository.selectSatisfying(new DelinquentInvoice());

DomainmodelandDataaccess


SimpleMapping


@Entitypublic class Plant {

@Id@GeneratedValue(strategy = GenerationType.AUTO)private Long id;private String name;@Column(name="DESC")private String description;private Float price;@Lobprivate Image photo;

}

PLANT

ID NAME DESC PRICE PHOTO

Mappingofassociations


PLANT

ID NAME DESC PRICE

Plant

name: Stringdescription: Stringprice: Float

PurchaseOrderLine

start: Dateend: DatelineTotal: Float

PurchaseOrder

contact: Stringtotal: Float

PURCHASEORDERLINE

ID STARTD ENDD LINETOTAL PLANT_ID

@Entitypublic class PurchaseOrderLine {

@ManyToOneprivate Plant plant;

}

Mappingofassociations


PURCHASEORDER

ID CONT TOTAL

Plant

name: Stringdescription: Stringprice: Float

PurchaseOrderLine

start: Dateend: DatelineTotal: Float

PurchaseOrder

contact: Stringtotal: Float

PURCHASEORDERLINE

ID START END LINETOTAL PLANT

@Entitypublic class PurchaseOrder {

@OneToMany(cascade = CascadeType.ALL)private Set<PurchaseOrderLine> poLines

= new HashSet<PurchaseOrderLine>();

}

enum CascadeType {ALL, MERGE, PERSIST, REFRESH, REMOVE

}

PO_POL

PO_ID POL_ID

Queryingdomainobjects


BasicqueryingwithSpringDatarepositories


@Repositorypublic interface PlantRepository extends JpaRepository<Plant, Long> {

List<Plant> findByNameLikeAndPriceBetween(String name, Float low, Float hi);}

@Repositorypublic interface PlantRepository extends JpaRepository<Plant, Long> {

@Query("select p from Plant p " +"where p.name like ?1 and p.price between ?2 and ?3")

List<Plant> finderMethod(String name, Float low, Float hi);}

Textual operators

And Or Between LessThan

GreaterThan After Before IsNull

IsNotNull/NotNull Like NotLike StartingWith

EndingWith Containing OrderBy Not

In NotIn True False

QueryDSL


plantRepo.findAll(nameContains("Mini").and(isAvailableFor(period)))

MTAT.03.229 Enterprise System Integration...Hexagonal architecture DDD & DATA ACCESS LUCIANO...

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