I currently have a CoreData based App on the App Store that supports iCloud with both iOS and OS X devices. It is a "semi-document" based app; that's to say it's technically not a document based app but it manages multiple Core Data databases.
I've done this by creating my own class that manages a list of database names (e.g. Shopping/ToDo/e.t.c) and a system of instantiating multiple NSManagedObjectContexts based on these database names, using iCloud enabled NSPersistentStoreCoordinators.
I'd like to update the App soon (i.e. version 2) and have been reading about UIManagedDocument and NSPersistentDocument but this has caught my eye:
Note: In OS X, the NSPersistentDocument class does not support iCloud.
My question is: Is it possible to subclass NSPersistentDocument or set up a system whereby CoreData, iCloud and iOS and OS X can come together in a document based app?
Related
I am creating a swiftui app that uses cloudkit and core data. If the user is signed in to iCloud it will use both, if not it will only use core data. While testing I realized there are so many situations you have to take into account, ex: The user started off not signed into iCloud, then later signed in after using the app for a while. So now there's an issue with merging the cloud data and the recent core data.
I want to be able to ask the user if the want to use the backed-up data or the new data. How would I go about deleting the core data, and reloading the backed-up data, or vice versa
I'm currently learning how to use CloudKit Framework and lack of documentation or examples showing how to sync Core Data and CloudKit.
I have watched all WWDC videos (2014, 2015, 2016) Dedicated to CloudKit, but none of them telling us how to implement syncing with Core Data. I can't find any fresh examples, tutorial or books, showing how to implement this syncing.
I know that it is effective to use Operations API by CloudKit (not Convenience API) and to Subscribe to changes as it said in the new WWDC 2016 videos, dedicated to CloudKit, but mapping with CoreData is a real problem.
For example, let's say I would like to create an app similar to Notes app. while offline, user can create his notes and work with them saving them to his core data database. When the device going online the app checks what changed on the server and saves newly created records to server (CloudKit).
When the app starts, it also fetches for changes from the CloudKit and if there are changes , it updates local cache (Core Data) with the new changes.
I would appreciate to have a common pattern of syncing. Where to place syncing with Core Data methods and how they should look like?
Would appreciate any information or help about this.
I'm using Swift 3, Xcode 8 , iOS 10.
As of iOS 13, there are new API's that simplify this synchronization for developers. I would recommend you to watch the WWDC19 session about the new synchronization between CoreData and CloudKit. Please note that these new API's only work for iOS 13+.
Video: https://developer.apple.com/videos/play/wwdc2019/202/
In short, you need to start using NSPersistentCloudKitContainer instead of NSPersistentContainer. This will let the syncing work automatically using automatic conflict resolution with a last-writer-wins merge strategy. If you want to build a good working app, you'll also need to do some modifications to improve the syncing for your app.
Official documentation can be found at:
Setting Up Core Data with CloudKit
Syncing a Core Data Store with CloudKit
Data modeling for collaboration (conflict-free replicated data type)
At the end of the session they also demonstrated an example of better sync merging than the default 'last-writer-wins merge strategy'. The usage of Causal Trees allow multiple users to edit the same string (and to some extend other types of data) without losing any data. I would really recommend everyone to read this article from Archagon that describes how this works and how to implement it (also with CloudKit syncing, but not the new automatic one). As demonstrated in the session, you can also implement this with the new automatic syncing between CoreData and CloudKit.
Core Data already provides the user with the ability to sync to iCloud. There's no need to use CloudKit.
Design For Core Data In iCloud
But yes, Core Data with iCloud has been deprecated. Even so, it has not been discontinued, and there are no immediate plans at apple to discontinue it, they just want to discourage its use. But it also has problems with rationalising updates from multiple devices.
In any case, I have been looking into the question of how to do this with cloud kit myself. Two answers; the first is to use the following;
Seam in GitHub
The second is to do it manually;
Designing for CloudKit
The key here is that Cloud Kit needs the record metadata to be able to handle record updates reliably, so you have to save that metadata in your Core Data database. The CKRecord class includes a method encodeSystemFields(with:) which will encode those fields into a Data record that can be stored in your database, and then your can use the appropriate decoder when you need to restore the CKRecord.
Anyway, I am about to start doing this myself. I'll update this with more information when I have it.
Apple has recently published a guide that seems to answer this question. Check out Apple's Maintaining a Local Cache of CloudKit Records to see how to store CloudKit data on device.
While this guide doesn't provide sample code to write to the device, it does answer the rest of the question. This tells you how to fetch changes from CloudKit and create data which can be stored on the device.
I have a app that uses UIManagedDocument to initiate core data, i'm interested in using MagicalRecord.
users of the app may have 10 thousands of record in core data, so I want to avoid a manual data migration, so is there a way to initiate MagicalRecord using existing data store created by UIManagedDocument?
The app I'm working on at the moment has a read-only Core Data library full of questions (for kids to answer) that I'd like the freedom to quickly replace via app updates (ideally just by replacing the sqlite backend database in the user's documents folder if it's different to the version in the application bundle).
I'm also storing data created by the user that I don't want to lose when I replace the question database.
Is it feasible (and good practice) to have two persistent stores and data models in the same app, one which I can replace and one that remains, er, persistent through updates?
Yes. You can just have two separate Core Data stacks (two persistent stores, managed object models, and managed object contexts). Doing anything to one should not affect the other. If you want, they can also share the same managed object model, but it may be simpler to keep two separate ones if the two stores are completely independent.
I have a Phonegap/Cordova app that runs on iOS. It saves it's data into HTML5 localStorage.
I'm trying to work out if it's possible to sync the localStorage data (using iCloud) to other iOS devices, and even OS X.
From what I can see, in iOS localStorage is actually implemented as a SQLite database, which (when using Phonegap/Cordova) is written to the app's Documents directory:
Documents/Backups/localstorage.appdata.db
I also understand that there are three main ways of storing data in iCloud:
Key/Value storage
UIDocument / NSDocument
Core Data
I know I can't use the Key/Value iCloud storage method, because I have more than 1MB of data to store, and the limitation is 1MB per app with that method.
This question, I believe is talking about the UIDocument method, and asks if it is possible to store a SQLite db file in iCloud using that method. The answer is no because the database may become corrupted.
So that really leaves the Core Data method.
So my question is - would this work? Could I sync the localStorage.db file to iCloud using Core Data?
I've never used Core Data and don't know much about it. I'm just wondering if it would be possible, or if there is something else I don't understand.
Are there any other ways to sync localStorage data between iOS devices or OS X ?
The answer unfortunatly appears to be no, Core Data cannot be used with HTML5 localStorage
Core Data can not be used with SQLite databases other than ones created with Core Data. If you try to, you get this error in XCode:
SQLite error code:1, 'no such table: Z_METADATA'
This is explained the Core Data docs:
https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdFAQ.html#//apple_ref/doc/uid/TP40001802-SW2
Although Core Data supports SQLite as one of its persistent store
types, the database format is private. You cannot create a SQLite
database using native SQLite API and use it directly with Core Data
(nor should you manipulate an existing Core Data SQLite store using
native SQLite API)
I still want to solve this issue though. I'm thinking of creating a Javascript API that mirrors the localStorage API. This would be a phonegap plugin that can call objective-c code, and effectively write it's changes to a Core Data database. The Core Data database should then be able to be synced to iCloud.
If it works, I'll come back and update this answer.