Downloaded 15 times
Uploaded byMake School
Advanced Core Data
Managed Object Contexts cannot be shared across threads and objects cannot be passed between threads. Core Data supports concurrency through contexts with different queue types (main vs private queue). Child contexts allow sharing objects and changes with a parent context on a different thread or for temporarily storing changes. Core Data supports migrations to handle changes to the data model over time through lightweight and custom migrations.
More Related Content
Advanced Core Data
- 2.
- 3. AGENDA Concurrency Child & ParentContexts Migrations
- 4.
- 5. CORE DATA ANDCONCURRENCY Managed Object Contexts cannot be used from multiple threads Managed Objects cannot be passed between threads - you need to refetch them on each thread using the ManagedObjectID of the object you’re trying to retrieve
- 6. CORE DATA ANDCONCURRENCY Two different concurrency types for Managed Object Contexts: NSMainQueueConcurrencyType contexts with this concurrency type can only be used from the main thread NSPrivateQueueConcurrencyType contexts with this concurrency type can only be used from the private queue they own; need to use performBlock to dispatch to private queue
- 7. CORE DATA ANDCONCURRENCY let jsonArray = … //JSON data to be imported into Core Data let moc = … //Our primary context on the main queue let privateMOC = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType) privateMOC.parentContext = moc privateMOC.performBlock { for jsonObject in jsonArray { let mo = … //Managed object that matches the incoming JSON structure //update MO with data from the dictionary } do { try privateMOC.save() } catch { fatalError("Failure to save context: (error)") } } Source: Example from Apple Documentation
- 8. CHILD & PARENTCONTEXTS
- 9. CHILD & PARENTCONTEXTS Child Context Main Context Unsaved Changes Child Context Main Context Child Context Main Context Unsaved Changes New Unsaved Changes Child Context Saved Changes persisted (1) (2) (3)
- 10. CHILD & PARENTCONTEXTS Two main use cases for child contexts: Threading: work with Core Data from a background thread by using a Private Queue child context Temporary changes: Allows users to discard changes without saving them by keeping modifications in a child context
- 11.
- 12. MIGRATIONS The data modelof your application will change over time You need to be able to load data from an older version of the data model and migrate them to the new one For small changes (adding properties, renaming properties, etc.) Core Data can perform lightweight migrations out of the box Some changes require custom migrations
- 13.
- 14. SUMMARY Core Data’s ManagedObject Context and Managed Object classes are not thread safe Core Data can be used from background thread by using a separate context with a private queue A context can have a parent context - this is useful for threading and change management Core Data supports migrations, in many cases lightweight migrations will work out of the box
- 15.
- 16. ADDITIONAL RESOURCES Core DataProgramming Guide: Concurrency Core Data Model Versioning and Data Migration