{"id":45136,"date":"2024-09-27T15:55:21","date_gmt":"2024-09-27T19:55:21","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=45136"},"modified":"2024-09-27T15:55:21","modified_gmt":"2024-09-27T19:55:21","slug":"nsmanagedobjectid-and-persistentidentifier","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2024\/09\/27\/nsmanagedobjectid-and-persistentidentifier\/","title":{"rendered":"NSManagedObjectID and PersistentIdentifier"},"content":{"rendered":"

Fatbobman<\/a>:<\/p>\n

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However, in SwiftData, there is currently no similar property or method to directly determine the [temporary] state of a PersistentIdentifier<\/code>. Since SwiftData’s mainContext<\/code> defaults to the autoSave<\/code> feature (developers do not need to explicitly save data), identifiers may temporarily be unusable in other contexts after creating data objects.<\/p>\n

[…]<\/p>\n

SwiftData’s default implementation is still based on Core Data, so the format of PersistentIdentifier<\/code> is very similar to that of NSManagedObjectID<\/code>[…]<\/p>\n<\/blockquote>\n

You can see this when printing it, but crucially there is still no API to convert between the two types.<\/p>\n\n

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Starting with Xcode 16, the Core Data framework has officially annotated [NSManagedObjectID<\/code> as Sendable<\/code>], so developers no longer need to do it manually.<\/p>\n<\/blockquote>\n

It’s interesting that it took so long since NSManagedObjectID<\/code> has always been threadsafe outside of Swift Concurrency.<\/p>\n

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Although an NSManagedObjectID<\/code> instance contains sufficient information to indicate the data post-persistence, it cannot retrieve the corresponding data when used with another NSPersistentStoreCoordinator<\/code> instance, even if the same database file is used. In other words, an NSManagedObjectID<\/code> instance cannot be used across coordinators.<\/p>\n

This is because the NSManagedObjectID<\/code> instance also includes private properties of the corresponding NSPersistentStore<\/code> instance.<\/p>\n<\/blockquote>\n

I kind of look at it backwards from this. The NSManagedObjectID<\/code> doesn’t<\/em> contain very much information—it’s often squeezed into a tagged pointer. How is this possible when it logically contains a reference to the entity description and the persistent store, in addition to the primary key? I assume that it’s storing abbreviations for these, which can only be interpreted with respect to a coordinator.<\/p>\n\n

Previously:<\/p>\n