Core Data - objc.io

271 Pages·2016·2.573 MB·English

by  Florian Kugler, Daniel Eggert

Version2.0(December2016)
©2016Kugler,EggertundEidhofGbR
AllRightsReserved
Formorebooksandarticlesvisitusathttp://objc.io
Email:[email protected]
Twitter:@objcio
Introduction
HowThisBookApproachesCoreData 9
ANoteonSwift 11
Part1
CoreDataBasics
1 HelloCoreData
CoreDataArchitecture 16
DataModeling 17
SettingUptheStack 20
ShowingtheData 22
ManipulatingData 30
Summary 36
NotesforPre-iOS10/macOS10.12 37
2 Relationships
AddingMoreEntities 40
Subentities 43
CreatingRelationships 46
OtherTypesofRelationships 48
EstablishingRelationships 50
RelationshipsandDeletion 54
AdaptingtheUserInterface 57
Summary 59
3 DataTypes
StandardDataTypes 61
PrimitivePropertiesandTransientAttributes 63
CustomDataTypes 64
DefaultValuesandOptionalValues 71
Summary 72
Part2
UnderstandingCoreData
4 AccessingData
FetchRequests 76
Relationships 85
OtherWaystoRetrieveManagedObjects 86
MemoryConsiderations 87
Summary 89
5 ChangingandSavingData
ChangeTracking 92
SavingChanges 94
BatchUpdates 99
Summary 101
6 Performance
PerformanceCharacteristicsoftheCoreDataStack 104
AvoidingFetchRequests 108
OptimizingFetchRequests 116
InsertingandChangingObjects 123
HowtoBuildEfficientDataModels 124
StringsandText 128
EsotericTunables 128
Summary 128
Part3
ConcurrencyandSyncing
7 SyncingwithaNetworkService
OrganizationandSetup 131
SyncingArchitecture 133
ContextOwner 134
ReactingtoLocalChanges 137
ReactingtoRemoteChanges 141
ChangeProcessors 142
DeletingLocalObjects 145
GroupsandSavingChanges 146
ExpandingtheSyncArchitecture 147
8 WorkingwithMultipleContexts
ConcurrencyRules 152
MergingChanges 158
TheDefaultConcurrentSetup 159
SetupswithMultipleCoordinators 161
SetupswithNestedContexts 163
ComplexityofNestedContexts 167
Summary 172
9 ProblemswithMultipleContexts
SaveConflictsandMergePolicies 175
QueryGenerations 181
DeletingObjects 183
UniquenessConstraints 187
Summary 189
Part4
AdvancedTopics
10 Predicates
SimplePredicates 193
CreatingPredicatesinCode 195
FormatStrings 195
CombiningPredicates 199
TraversingRelationships 201
MatchingObjectsandObjectIDs 203
MatchingStrings 204
TransformableValues 206
PerformanceandOrderingExpressions 207
Summary 208
11 Text
TheComplexityofUnicode 210
Searching 211
Sorting 215
Summary 220
12 ModelVersionsandMigratingData
ModelVersions 222
TheMigrationProcess 225
InferredMappingModels 234
CustomMappingModels 235
MigrationandtheUI 240
TestingMigrations 241
Summary 243
13 Pro(cid:297)ling
SQLDebugOutput 245
CoreDataInstruments 252
ThreadingGuard 256
Summary 256
14 RelationalDatabaseBasicsandSQL
AnEmbeddedDatabase 259
Tables,Columns,andRows 260
ArchitectureoftheDatabaseSystem 261
TheDatabaseLanguageSQL 264
Relationships 266
Transactions 269
Indexes 269
Journaling 270
Summary 271
Introduction
CoreDataisApple’sobjectgraphmanagementandpersistencyframeworkforiOS,
macOS,watchOS,andtvOS.Ifyourappneedstopersiststructureddata,CoreDataisthe
obvioussolutiontolookinto:it’salreadythere,it’sactivelymaintainedbyApple,andit
hasbeenaroundformorethan10years.It’samature,battle-testedcodebase.
Nevertheless,CoreDatacanalsobesomewhatconfusingatfirst;it’sflexible,butit’snot
obvioushowtobestuseitsAPI.Thatsaid,thegoalofthisbookistohelpyougetofftoa
flyingstart.Wewanttoprovideyouwithasetofbestpractices—rangingfromsimpleto
advancedusecases—sothatyoucantakeadvantageofCoreData’scapabilitieswithout
gettinglostinunnecessarycomplexities.
Forexample,CoreDataisoftenblamedforbeingdifficulttouseinamultithreaded
environment.ButCoreDatahasaveryclearandconsistentconcurrencymodel.Used
correctly,ithelpsyouavoidmanyofthepitfallsinherenttoconcurrentprogramming.
Theremainingcomplexitiesaren’tspecifictoCoreDatabutrathertoconcurrencyitself.
Wegointothoseissuesinthechapteraboutproblemsthatcanoccurwithmultiple
contexts,andinanotherchapter,weshowapracticalexampleofabackgroundsyncing
solution.
Similarly,CoreDataoftenhasthereputationofbeingslow.Ifyoutrytouseitlikea
relationaldatabase,you’llfindthatithasahighperformanceoverheadcomparedto,for
example,usingSQLitedirectly.However,whenusingCoreDatacorrectly–treatingitas
anobjectgraphmanagementsystem–thereareactuallyquiteafewplaceswhereitends
upbeingfasterduetoitsbuilt-incachesandobjectmanagement.Furthermore,the
higher-levelAPIletsyoufocusonoptimizingtheperformance-criticalpartsofyour
applicationinsteadofreimplementingpersistencyfromscratch.Throughoutthisbook,
we’llalsodescribebestpracticestokeepCoreDataperformant.We’lltakealookathow
toapproachperformanceissuesinthededicatedchapteraboutperformance,aswellas
intheprofilingchapter.
How This Book Approaches Core Data
ThisbookshowshowtouseCoreDatawithworkingexamples—it’snotanextended
APImanual.Wedeliberatelyfocusonbestpracticeswithinthecontextofcomplete
examples.Wedosobecause,inourexperience,stringingallthepartsofCoreData
togethercorrectlyiswheremostchallengesoccur.
Inaddition,thisbookprovidesanin-depthexplanationofCoreData’sinnerworkings.
Understandingthisflexibleframeworkhelpsyoumaketherightdecisionsand,atthe
sametime,keepyourcodesimpleandapproachable.Thisisparticularlytruewhenit
comestoconcurrencyandperformance.
SampleCode
YoucangetthecompletesourcecodeforanexampleapponGitHub.We’reusingthis
appinmanypartsofthebooktoshowproblemsandsolutionsinthecontextofalarger
project.We’veincludedthesampleprojectinseveralstagessothatthecodeonGitHub
matchesupwiththecodesnippetsinthebookasbestaspossible.
Structure
Inthefirstpartofthebook,we’llstartbuildingasimpleversionofourappto
demonstratethebasicprinciplesofhowCoreDataworksandhowyoushoulduseit.
Eveniftheearlyexamplessoundtrivialtoyou,westillrecommendyougooverthese
sectionsofthebook,asthelater,morecomplexexamplesbuildontopofthebest
practicesandtechniquesintroducedearlyon.Furthermore,wewanttoshowyouthat
CoreDatacanbeextremelyusefulforsimpleusecasesaswell.
Thesecondpartfocusesonanin-depthunderstandingofhowallthepartsofCoreData
playtogether.We’lllookindetailatwhathappenswhenyouaccessdatainvariousways,
aswellaswhatoccurswhenyouinsertormanipulatedata.Wecovermuchmorethan
what’snecessarytowriteasimpleCoreDataapplication,butthisknowledgecancome
inhandyonceyou’redealingwithlargerormorecomplexsetups.Buildingonthis
foundation,weconcludethispartwithachapteraboutperformanceconsiderations.
Thethirdpartstartswithdescribingageneralpurposesyncingarchitecturetokeepyour
localdatauptodatewithanetworkservice.Thenwegointothedetailsofhowyoucan
useCoreDatawithmultiplemanagedobjectcontextsatonce.Wepresentdifferent
optionstosetuptheCoreDatastackanddiscusstheiradvantagesanddisadvantages.
Thelastchapterinthispartdescribeshowtonavigatetheadditionalcomplexityof
workingwithmultiplecontextsconcurrently.
Thefourthpartdealswithadvancedtopicslikeadvancedpredicates,searchingand
sortingtext,howtomigrateyourdatabetweendifferentmodelversions,andtoolsand
techniquestoprofiletheperformanceofyourCoreDatastack.Italsoincludesachapter
thatintroducesthebasicsofrelationaldatabasesandtheSQLquerylanguagefromthe
perspectiveofCoreData.Ifyou’renotfamiliarwiththese,itcanbehelpfultogothrough