2014-07-22-OSCON-Creating-Models-16x9.pdf

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1、CreatingModelsRobAllen,July2014Haveyoureadthese?ThebusinesslogicisthehardpartThemodelisthesolutiontoaproblemAfantasticsolution!What’sinthemodel?What’sinthemodel?DomainPersistenceApplicationThedomainAproblemAcustomerwantstoplanajourneybetweentwostations.!Howdowem

2、odelthis?Identifythekeyobjects•Customer!•Journey!•Station!•LineEntity–relationshipdiagramEntitiesrepresentthingsintheproblem-spaceEntity•Meanssomethingtothecustomer!•Anobjectdefinedprimarilybyitsidentity!•Mutable!•Persisted!•HasalifecycleIdentity•Theidentityofano

3、bjectiswhatitmeanstothecustomer!•UniquewithinthescopeofthedomainForatubestation,thisisit’sname,notitsdatabaseid.Valueobjects•Definedprimarilybyitsattributes!•Immutable!•Simple!!•DonotexistwithoutanentityAstationhasalocationAstationhasalocationDomainservicesIfaSER

4、VICEweredevisedtomakeappropriatedebitsandcreditsforafundstransfer,thatcapabilitywouldbelonginthedomainlayer.–EricEvansDomainservices•Wemapthebusinessprocessestoservices!•Representsbehaviourinthedomain!•Aservicedoesnothaveinternalstate!•Usuallyapointofconnectionf

5、ormanyobjectsLet’slookatsomecodeSomecodeclassJourney{functiongetStart(){}functionsetStart(Station$start){}functiongetStop(){}functionsetStop(Station$stop){}functionsetRoute(){}functiongetRoute(){}}classRoutingService{functionroute(Station$start,Station$stop){}}S

6、omecodeclassJourney{functiongetStart(){}functionsetStart(Station$start){}functiongetStop(){}functionsetStop(Station$stop){}functionsetRoute(){}functiongetRoute(){}}classRoutingService{functionroute(Station$start,Station$stop){}}SomecodeclassJourney{functiongetSt

7、art(){}functionsetStart(Station$start){}functiongetStop(){}functionsetStop(Station$stop){}functionsetRoute(){}functiongetRoute(){}}classRoutingService{functionroute(Station$start,Station$stop){}}AnaemicdomainmodelYourealizethatthereishardlyanybehaviorontheseobje

8、cts,makingthemlittlemorethanbagsofgettersandsetters.!!Insteadthereareasetofserviceobjectswhichcaptureallthedomainlogic.–MartinFowlerEntitywithbehaviourclassJourney{fu