Daniel Eggert's Slides at NSSpain 2013

NSSpain is an iOS & OSX developers conference in Spain.
More info: http://nsspain.com

Transcript

1. Core Data — best practices Daniel Eggert NSSpain, Logroño September 18, 2013
2. Daniel Eggert Me & Core Data
3. Agenda • What is Core Data? • Core Data Stack & Data Model • Relationships • Getting Data from Core Data • Performance • Advanced Core Data
4. What is Core Data?
5. What is Core Data? • Objective-C • Mature Code Base — 8 years in the wild • OS X since 10.4 • iOS since iOS 3 • No UI
6. What is Core Data? • (Very powerful) object graph management • Persistency technology • Not an SQL wrapper • Not a Object-relational mapping (O/RM)
7. Meet the Stack
8. Core Data Stack NSManaged Object NSManaged Object NSManaged Object NSManaged Object
9. NSPersistent StoreCoordinator SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store NSPersistent Store NSPersistent Store SQLite File System SQLite File System Core Data Stack
10. Core Data Stack NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
11. Core Data Stack NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System { { Object Graph Management Persistence
12. Core Data Stack NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object
13. Core Data Stack NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object
14. Core Data Stack NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object
15. Meet the Model
16. © Jimmy Rodriguez www.jimmy-rodriguez.book.fr
17. Core Data Model
18. Core Data Model Berlin Bilbao Logroño Paris San Francisco Copenhagen
19. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Core Data Model
20. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
21. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain “Route” Entity “City” Entity
22. entity |ˈɛntɪti| noun ( pl. entities ) a thing with distinct and independent existence: Church and empire were fused in a single entity. “Route” Entity “City” Entity
23. Model & Relationships Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
24. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
25. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Data
26. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
27. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Relationships
28. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
29. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Boring Part
30. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
31. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain Where the Fun Happens
32. Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
33. Context Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain
34. NSManagedObjectContext Berlin Bilbao Logroño Paris San Francisco Copenhagen Denmark WWDC NSSpain NSManagedObjectContext
35. Relationships
36. Relationships
37. Relationships Object Graph Management
38. Relationships NSSpain Route *nsspain = ...
39. Relationships NSSpain Route *nsspain = ... cities = nsspain.cities;
40. Berlin Bilbao Logroño NSSpain Relationships NSSpain Route *nsspain = ... cities = nsspain.cities;
41. Relationships cities = nsspain.cities; Berlin Bilbao Logroño NSSpain
42. Relationships cities = nsspain.cities; Berlin Bilbao Logroño NSSpain berlin = cities[0];
43. Relationships cities = nsspain.cities; Berlin Bilbao Logroño NSSpain berlin = cities[0]; otherRoutes = berlin.routes;
44. Berlin Bilbao Logroño Denmark WWDC NSSpain Relationships cities = nsspain.cities; Berlin Bilbao Logroño NSSpain berlin = cities[0]; otherRoutes = berlin.routes;
45. Relationships Route *nsspain = ... NSOrderedSet *cities = nsspain.cities; City *berlin = cities[0]; NSSet *otherRoutes = berlin.routes;
46. Getting Data from Core Data © Phil Hobgen http://500px.com/philhobgen
47. Use Relationships
48. Use Relationships Really!
49. Use Relationships Really! Really!
50. NSFetchRequest
51. NSFetchRequest What does a do?
52. NSFetchRequest NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
53. NSFetchRequest NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
54. Traversing Relationship NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
55. Traversing Relationship NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
56. NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
57. NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
58. NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System Expensive
59. Never use NSFetchRequest, right?
60. When to use NSFetchRequest • Searching • All objects • Pre-fetching
61. Searching NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
62. Searching • NSFetchRequest allows you to set a predicate • NSPredicate specify what you want to fetch • Target your search • Less I/O → better performance • Only bring in those objects you want • Core Data doesn’t have to pull in data you don’t need
63. Searching • Check Xcode documentation called “Core Data Snippets” for a lot of good info on predicates.
64. All Objects • Showing a list of all objects to the user • UITableView • UICollectionView • You must not bring in all objects at once • You must not bring in each object on its own
65. All Objects NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
66. All Objects • Use “batching”: fetchRequest.fetchBatchSize = 40; depends on your app
67. All Objects fetchRequest.fetchBatchSize = 3; don’t use 3 in a real app 1 2 3 4 5 6 7 8 9 10 11 12
68. All Objects fetchRequest.fetchBatchSize = 3; don’t use 3 in a real app 1 2 3 4 5 6 7 8 9 10 11 12
69. All Objects fetchRequest.fetchBatchSize = 3; don’t use 3 in a real app 1 2 3 4 5 6 7 8 9 10 11 12
70. All Objects fetchRequest.fetchBatchSize = 3; don’t use 3 in a real app 1 2 3 4 5 6 7 8 9 10 11 12
71. All Objects fetchRequest.fetchBatchSize = 3; don’t use 3 in a real app 1 2 3 4 5 6 7 8 9 10 11 12
72. Pre-Fetching • Round tripping to the Database is Expensive • Fetch as much as possible in 1 go NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
73. Pre-Fetching • Execute an NSFetchRequest without using its result. Just to bring objects into the context • Only do this when you need to. • Don’t fetch objects if they’re already in the context (or the persistent store coordinator’s row cache) • Measure • Don’t prematurely optimize
74. Pre-Fetching NSManagedObject *mo = ...; mo.isFault [mo hasFaultForRelationshipNamed:]
75. Performance © John Bender http://500px.com/bendersama
76. Performance Issues Top 3 • Loading too much data • Not loading enough data • Inefficient queries These 3 are a problem in any database application, not just Core Data, but people like to blame Core Data.
77. Loading too much data • Loading everything is BAD • batching • aggregating • Sorting and filtering in memory is BAD • predicates • sort descriptors
78. Not loading enough data • Round trips to the file system are SLOW • Relationship prefetching
79. Inefficient Queries • Use indexes
80. Inefficient Queries • Unicode text searching is expensive, but necessary • normalize text (uppercase, diacritics) • ‘like’ is expensive! • beginswith and contains are a lot faster than like
81. Inefficient Queries • Order of predicates matters! • Cheap stuff at the beginning • Relationships at the end • Xcode Documentation: “Predicates” Guide
82. Performance Debugging -com.apple.CoreData.SQLDebug 1 and / or EXPLAIN QUERY PLAN ...
83. © Derek Bruff http://500px.com/derekbruff Advanced Core Data
84. Multi-Context Multi-Store Core Data support various, complex setups NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
85. Multi-Context NSPersistent StoreCoordinator SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store Contexts are distinct — distinct changes. NSManagedObject tied to their owning context.
86. Multi-Store No relations across stores. NSPersistent StoreCoordinator SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store NSPersistent Store NSPersistent Store SQLite File System SQLite File System
87. Multi-Stack NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
88. Mixing everything NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System NSPersistent StoreCoordinator SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store NSPersistent Store NSPersistent Store SQLite File System SQLite File System
89. Complex Stacks • Very, very flexible • Also adds a lot of complexity • Threading is always complex • You NEED a merging policy • You can almost always do without • Save yourself the trouble — go for simple
90. Parent-Child Context • Don’t use it — it’s more complicated than it seems • Implemented to facilitate deferred saving (UIManagedDocument) NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object
91. Parent-Child Context • There’s a lot of locking that NEEDS to happen • NSManagedObjectID behaves differently NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object
92. Incremental Store • Don’t use it — it’s (a lot) more complicated than it seems
93. Incremental Store NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object NSPersistent Store SQLite File System
94. NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object Your own code here ? Incremental Store
95. NSPersistent StoreCoordinator NSManagedObjectContext NSManaged Object NSManaged Object NSManaged Object NSManaged Object Your own code here ? Incremental Store • Transactional ?!? • Threading / Async ?!?
96. Why Core Data? • Relationships • Delete Propagation • Change Tracking and Undo • Scratchpad • Faulting • Uniquing
97. Why Core Data? • Very mature code base — more than 8 years • Battle tested • Very performant if used right
98. Covered Today • What is Core Data? • Core Data Stack & Data Model • Relationships • Getting Data from Core Data • Performance • Advanced Core Data
99. More Information • Check the Xcode Documentation • “Core Data Starting Point” • “Core Data Programming Guide” • “Core Data Snippets” • http://www.objc.io/issue-4/
100. Daniel Eggert @danielboedewadt http://www.objc.io/ Senior Software Developer Zeta Project GmbH, Berlin We’re hiring!
101. A & Q NSSpain