Introducing about Core Data which include stack, operation, and concurrency. In the final, talking about some my experiences.

1. Core Data
Neo

2. Outline
Core Data Introduction
Core Data Stack
Core Data Operation
Core Data Concurrency
Experience
Reference:
https://developer.apple.com/library/watchos/documentation/Cocoa/Conceptual/
CoreData/index.html

3. Core Data Introduction
What is the Core Data
Core Data is not RDBS, it’s ORM
It’s a framework to manage the model layer object, not a DBMS
Intelligent and efficiency data management tools
Advantage in Core Data
Efficiency data r/w, ex:lazy loading, faulting pre-fetching, etc…
Intelligent data schema upgrade & migration
Schema version control
Data editing in memory, save changes back to store

4. Simple to know stack vs. RMDB
Core Data Stack
tables
table
configuration
file.sql
files

5. Core Data Stack

6. Establish a Core Data stack
Core Data Stack

7. Core Data Stack

8. Core Data Operation

9. Core Data Operation
Request data from fetchResultsController
Request data from executeFetchRequest

10. Core Data Operation
Insert new data to MOC
Delete data from MOC
Modify data in MOC
Save change from MOC to PSC

11. Core Data Operation
If you set delegate to fetchResultsController, then
you can monitor what change in the MOC

12. Core Data Concurrency
Core data supports concurrency operation and
easy to implement, there are two ways
Child Managed Object Context
Another Managed Object Context but same Persistent Store Coordinator
(Not recommend anymore)
What time does we need it
a lot of executions in core data, ex:insert, delete, or update
A complex query which need a long time
App is almost waiting for core data access
The advantage is performance improvement when
App has data access performance issue.

13. Core Data Concurrency
Shouldn’t easy to try it if no performance issue
Program would be more complex, and access data operation too.
Managed Object Context is not thread-safe
Data is needed to care about conflict and merge.
Data is may not synced when miss some operations

14. Core Data Concurrency
Select one concurrencyType when create MOC
NSConfinementConcurrencyType
Default type for backward, it’s for keeping MOC is accessed in the thread
which it is created. (Deprecated in iOS 9.0)
NSPrivateQueueConcurrencyType (child MOC)
Create a private queue by GCD, it won’t block mainThread.
NSMainQueueConcurrencyType (main MOC)
MOC is accessed in mainThread, it would block UI.

15. Core Data Concurrency
Child Concurrency architecture

16. Core Data Concurrency
Asynchronous Saving
When you have heavy I/O
in core data

17. Core Data Concurrency
Operation of child MOC is the same as parent
MOC, but there are something important
Pass the MO to different MOC that is forbidden
Child MOC save just update data of parent MOC, it won’t save data to
disk.
Before child MOC save, data of parent MOC won’t have any change,
also parent MOC can’t find data which belong to child MOC.
Is only the architecture?
NO, but I don’t think that need more concurrency architectures in the
most normal cases.

18. Experience
We got the Core Data fundamental now, but
something which need to be known in my experience

19. Experience
Pass MO between different contexts
We can’t pass MO directly
Use NSManagedObjectID to access MO from persistentStore or memory.
MO status maybe is not consistent
ex: MO is changed in child MOC without save, and the change won’t
affect the MO in parent MOC.
NSManagedObjectID has two status
PersistentID
The MO is saved back to persistent store, and can be accessed anywhere
by objectID
TemporaryID
The MO is no saved before, and it can’t be accessed from context.
After saved MO, you can’t find object by the ID!!
BTW, you can check the ID status by isTemporaryID

20. Experience
There are three methods access MO by objectID
objectWithID
Always return a MO, whatever it has data or not.
It can accessed parent’s temp MO in child, but that’s a new one.
Don’t use return value as Bool, it always get a empty data MO!!
objectRegisteredForID
Return MO if existed in MOC, otherwise return nil.
Ex: a MO saved in parent MOC, the method can’t access it in child
MOC.
existingObjectWithID
Return MO if it has been saved before, otherwise return nil.

21. Experience
MO has some status properties
isFault, isDeleted, faultingState, isInserted, isUpdated, isTemporaryID,
hasChanges
These status can be checked what they do in context
These status would be reset after saved
isDeleted
If delete MO and it’s no saved before, then the MO would be nil directly
If delete MO and it’s saved before, then only isDelete property would be changed
After deleted MO, it always existed if it was saved before!!
Check MO is deleted
Sometimes isDeleted can’t really know MO is deleted or not
Using existingObjectWithID and managedObjectContext
Check condition should be: (MO.isDelete || ![MOC exist..ID:MOID] || !
MO.managedObjectContext)

22. Experience
MO Update
Without save, change MO in the child MOC won’t affect attribute/status
MO in the parent MOC, otherwise, too.
Without save, insert MO in the child MOC won’t affect MO in the
parent MOC, otherwise, child MOC would be affected.
You can try core data operation in my testbed
https://github.com/flamelad/CoreDataTestbed

23. Q & A