Avi Tsadok

Unleash Core Data

Fetching Data, Migrating, and Maintaining Persistent Stores

Avi Tsadok
Tel Mond, Israel
ISBN 978-1-4842-8210-6e-ISBN 978-1-4842-8211-3
https://doi.org/10.1007/978-1-4842-8211-3
© Avi Tsadok 2022
This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed.
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This Apress imprint is published by the registered company APress Media, LLC, part of Springer Nature.

The registered company address is: 1 New York Plaza, New York, NY 10004, U.S.A.

The choice of writing on a vast subject such as Core Data is truly a fascinating journey. But, even that journey could not be achieved without the help of my close ones. Therefore, I would like to thank my family – my kids, Harel and Maya, and my loving wife, Tammy, who gave me the time and strength to sit down, investigate, dig, and write. Without your unconditional support, this book would not exist.

Table of Contents
Chapter 1:​ Welcome to Core Data 1
How I Met Core Data 1
Why Is Core Data So Important?​ 2
Because It Defines Your Business 2
Because It Holds User Data 3
Because That’s What We Sync 3
A Little Bit About Core Data History 3
NeXT and Enterprise Objects Framework 4
Core Data Was Born 5
What Will You Learn in This Book?​ 6
Should You Be Using Core Data?​ 6
How to Read This Book?​ 7
Let’s Begin! 7
Chapter 2:​ Core Data Basics and Setup 9
What Exactly Is Core Data?​ 10
The Core Data Developer Experience 11
The Core Data Stack 11
Why “Stack”?​ 12
Creating the Core Data Stack 12
The Managed Data Model 13
The Persistent Store 18
The Context 24
Core Data Container 26
Accessing Context 26
More Configurations 27
Let Apple Create the Container for Us 29
Summary 34
Chapter 3:​ The Data Model 35
The Importance of the Core Data Model 36
The Core Data Model Editor 36
The Entity 38
Entity Examples 38
Adding a New Entity 39
Attributes 39
Generated Classes 44
How Is Your Data Model Really Created 44
What Is NSEntityDescript​ion?​ 46
Welcome, NSManagedObject 47
Attributes Inspector 57
Optional 58
Transient 59
Default Value 59
Use Scalar Type 60
More Settings 62
Summary 63
Chapter 4:​ Relationships 65
Some Theory First 66
One-to-Many 66
Many-to-Many 67
One-to-One 67
Relationships in SQL Tables 68
Back to Xcode 69
Creating Our First Relationship 70
Configure Our Relationship 72
Let’s Take a Breath 78
Editor Style 79
Let’s Return to Code 81
Connecting Entities Together 82
A Relationship to Itself 85
Summary 86
Chapter 5:​ Contexts 87
What Are Contexts?​ 88
The Concept 88
Creating a Context 89
Manipulating Data 90
Insert New Objects 90
Fetching Objects 92
Delete Objects 97
Predefined Fetch Requests 97
More Predefined Fetch Request Configurations 101
Use Predefined Fetch Requests 102
Multiple Contexts 103
Multiple Main Contexts 104
Optimistic Locking 104
Nested Managed Object Contexts 111
Summary 115
Chapter 6:​ Fetching Data 117
Meet NSPredicate (Again) 118
Predicate Syntax 119
AND/​OR 120
Compound Predicates 120
Substitution Variables 122
Working with Strings 123
Equal 123
BEGINSWITH and ENDSWITH 124
LIKE:​ Wildcard Searches 125
CONTAINS 126
MATCHES 126
Numbers 127
Key Path Collection Queries 127
Relationships 131
To-One 131
To-Many 132
IN 135
Debugging 137
Console 137
Launch Arguments 138
Playgrounds 140
External Data Editor 143
Summary 144
Chapter 7:​ Implementation 145
Boundaries and Separations 146
Isolation 146
Protocols 148
Core Data Everywhere 149
Network Objects 149
Meet DTOs:​ Data Transfer Objects 150
Creating DTOs 151
Let’s Make It Dynamic 151
Working with the UI Layer 153
What Do We Want?​ 153
Observing Data Changes Using Notifications 154
NSFetchedResults​Controller 156
Undo 169
Why Do I Need It?​ 170
Meet UndoManager 170
Grouping 171
Summary 172
Chapter 8:​ Concurrency and Declarative Programming 173
These Rules Are Written in Blood 174
Contexts Are Not Thread-Safe 174
Managed Objects Belong to Their Context Thread 175
Writing in Private Context, Reading in Main Context 175
Private Contexts 175
Creating 176
Performing Actions 176
Concurrency Patterns 179
Parent/​Child Strategy 180
Private in Front 183
What to Choose?​ 186
Declarative Programming 187
SwiftUI and Core Data 189
Import Data from the Web to Core Data 195
Summary 197
Chapter 9:​ Performance 199
Faulting 199
Batch Faulting 202
Prefetching 203
Deleting 204
Improve Your Fetches 205
Fetch Index 206
Creating a Fetch Index 208
Index Expressions 212
Is a Fetch Index a Magic?​ 213
Use One-to-One Relationships to Improve Performance 213
Limit Your Results 214
String Search Optimization 215
Improve Our Saving 217
Batch Saving 217
Ordering + Relationships 219
Working with Instruments 220
A Few Words About Instruments 220
Opening Instruments 220
About Core Data Instruments 222
Core Data Saves Instrument 223
Faults and Fetches 225
Summary 227
Chapter 10:​ Migrations 229
Why Does Migration Happen?​ 230
Data Model Changes 230
Wait! Do You Really Need to Migrate?​ 232
The Migration Three Steps 232
Lightweight Migration 233
Adding a New Model Version 233
Modify the New Model Version 234
Setting the Current Model Version 235
Recompile and Open Our App 236
Mapping 236
Enable Lightweight Migration 238
Lightweight Migration Use Cases 239
Custom Mapping Migration 243
First Step:​ Create a New Version and Lock It 243
Create a Custom Mapping Model 244
Map Song->Note to NoteObject 247
Custom Migration Policy 252
Splitting the Song Entity 253
New Model Version and Mapping Model 253
Create Our Migration Policy 254
NSEntityMigratio​nPolicy 255
Removing the Song Entity from the Model Version 258
Summary 259
Chapter 11:​ Building a Custom Store Type 261
Custom Store:​ What Exactly Does It Mean?​ 262
Why Do We Need That?​ 263
Rely on Your Technology 263
Cross-Platform Support 263
Migrating from an Old Persistent Store 264
Connect the Persistent Store Directly to a Web Service 264
To Explore Another Stack Component 264
NSIncrementalSto​re vs.​ NSAtomicStore 265
How Do They Work?​ 265
NSPersistentStor​e 266
Registering the New Store 268
NSAtomicStore 268
Mapping the Data 269
Loading All the Data 269
Adding a New Object 272
Updating and Deleting 275
NSIncrementalSto​re 276
Loading the Store 276
Execute Store Requests 277
Faulting 283
Web Services 286
Summary 286
Chapter 12:​ Core Data and the World 289
Integrate with Spotlight 290
A Few Words About Spotlight 290
Core Data and Core Spotlight 290
“Index in Spotlight” 291
Persistent History Tracking 292
Create a Core Spotlight Delegate 293
Delete the Indexing 297
Small Note About Privacy 297
Share the Core Data Store with App Extensions 298
App Container 298
App Group 299
Working with the New Container Folder 301
Adding an Extension to an Existing App 303
Core Data and CloudKit 306
Set Up CloudKit 306
The Integration 308
Data Model Limitations 309
NSPersistentClou​dKitContainer 310
Add CloudKit to an Existing App 311
Summary 313
Chapter 13:​ What’s Next?​ 315
What Have We Learned Till Now?​ 315
How to Start?​ 316
Understand Your Needs 316
Design Your Data Model 317
Implementing Core Data 318
Where to Go from Here 319
Thanks 319
Index 321
About the Author
Avi Tsadok

is an accomplished iOS developer with almost a decade of experience. He is currently the head of mobile development at Melio Payments, a leading payments app. He’s also a regular contributor to “Better Programming” and has an active presence on Medium. Having written many iOS articles, he’s decided to combine his passion for writing and developing by writing his third book, along with “Pro iOS Testing” and “Mastering Swift Package Manager”.

 
About the Technical Reviewer
Felipe Laso

is a senior systems engineer working at Lextech Global Services. He’s also an aspiring game designer/programmer. You can follow him on Twitter at @iFeliLM or on his blog.

 
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