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ThingsIWishI'dKnownabout
CoreData
BeforeGettingMarried
CoreDataisawesome
❤
CoreDatabasics
Never
Never
1. create contexts on demand
BAD:Contextastransaction
GOOD:Nestedcontexts1
1
Described on Marcus Zarra article and video
EVENBETTER:Siblingcontexts2
2
Figures could be found on Five Agency blog
Never
1. create contexts on demand
2. write in main context
Hidesecondarycontextinaclosure,Luke
Hidesecondarycontextinaclosure,Luke
func storeUsers(jsonUsers: [JSON]) throws {
try container.writeInBackground { context in
for jsonUser in jsonUsers {
User.create(context).populate(with: jsonUser)
}
}
}
NSPersistentContainer
starting iOS 10.0
Never
1. create contexts on demand
2. write in main context
3. store a BLOB in an entity
Faulting
Never
1. create contexts on demand
2. write in main context
3. store a BLOB in an entity
4. use abstract entities
Ok,sometimes
Ifyoudonothaveplanstoimplementmigration.
Oh, wait...
Never
1. create contexts on demand
2. write in main context
3. store a BLOB in an entity
4. use abstract entities
5. use Swi! for Core Data
GOOD:DataModel
BAD:MappingModel
Always
Always
1. be ready for migration
Migrationmappingmodel:
!Inferred("lightweight")
or!Explicit
Multiplemodels
Serialmigration3
3
Good explanation and basic implementation could be found on Alexander Grebenyuk
Hugedatabasemigration
cancausetheapptocrash
!
Applerecommends
"multiplepasses"
Butanappcancrashanyway
¯_(ツ)_/¯
Always
1. be ready for migration
2. use autoreleasepool in loops
Always
1. be ready for migration
2. use autoreleasepool in loops
3. fetch only necessarily fields
ModifyNSFetchRequest
request.propertiesToFetch = ["employeeId", "employeeName"]
request.resultType = NSFetchRequestResultType.managedObjectResultType
request.returnsObjectsAsFaults = false
Always
1. be ready for migration
2. use autoreleasepool in loops
3. fetch only necessarily fields
4. use debug keys
EditschemeRunstage
-com.apple.CoreData.ConcurrencyDebug 1
-com.apple.CoreData.MigrationDebug 1
-com.apple.CoreData.SQLDebug 3
-com.apple.CoreData.Logging.stderr 1
Keepcalm
and
UseCoreData
Evgenii_Kamyshanov@epam.com
CoreDatacheatsheet
NEVER ALWAYS
Context on demand Prepare migration
Write in main context Use autoreleasepool
BLOB in entity Fetch particular fields
Abstract entity Use debug keys
Evgenii_Kamyshanov@epam.com

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