I'm using NSPersistentCloudKitContainer to sync and share some records between users with CloudKit and CoreData. Is working relatively well after adapting the sample code to my needs from the Apple website.
However NSPersistentCloudKitContainer has method called initializeCloudKitSchema to initialize and validate the CloudKit schema. What is the best practice to use it, as it seems it doesn't have a useful role (is not used in the Apple sample docs and code and the scheme is created anyway without it)?
You need to initialize your Schema each time you've made changes in your Core Data model, so these changes will be synched to iCloud and you will be able to deploy Schema / Schema changes to the Production.
After that you could comment out the lines related to initialization - there is no need to initialize the same Schema every time. Once you need to update the Schema, just comment these lines back in.
Related
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.
Here is my situation. I have an extensive REST based API that connects to a MongoDB database using Mongoose. The API is written as a standard "MEAN" stack application.
Currently, when a developer queries the API they're always connecting to the live production database. What I want to do is have an exact duplicate database as a "staging" database, where new data will be added first, vetted over a period of time, and then move to the live database. Then I want developers to be able to query either one simply by modifying their query.
I started looking into this with the Mongoose documentation, and it appears as though the models are tied to the DB connection, and if I want to have multiple connections I also have to have multiple models, one for each connection. This would be a nightmare of WET code and not the path I want to take.
What I want to do is not touch any of my code at all and simply have a switch that changes to the proper database for a given query. So my question is, how can I achieve this? Is it possible? The documentation seems to imply it is not.
Rather than trying to maintain connections two environments in the same code base have you considered setting up stage version of your application? Which database it connects to could be set through an environment variable or some other configuration option.
The developers would still then only have to make a change to query one or the other and you could migrate data from the stage database to production/live database once you have finished your vetting process.
I have an app with multiple updates on the AppStore already, funny thing happened, I thought that the lightweight migration happens automatically, however, my recent discovery that I need to add the
NSDictionary *storeOptions = #{NSMigratePersistentStoresAutomaticallyOption:#YES, NSInferMappingModelAutomaticallyOption:#YES};
to my persistentStoreCoordinator shook my confidence when I realized I already have 5 core data models.
The question is: when I add the above line to the next version of the app, is it going to work for everyone when they update? Because right now everything that happens when they open the app .. is a fancy CRASH.
Thx
It will work if automatic lightweight migration is possible for the migration you're trying to perform. Whether this will work depends on the differences between the model used for the existing data and the current version of the model. Many common changes permit automatic lightweight migration but not all. You'll need to review the docs on this kind of migration and decide whether it will work in your case.
If it doesn't work, there are other ways to handle it, for example by creating a mapping file to tell Core Data how to make changes that it can't infer automatically.
I am bit confused regarding which class I should inherit from. My application currently creates files in the "Documents" folder and also has Core Data based data models. These data models contains more information about the files.
Now I am thinking to migrate the app to the document architecture and thereby integrating with iCloud at one of time.
I have started to think in the direction of using both i.e. using UIDocument to manage the files and UIManagedDocument to manage the Core Data.
Would appreciate if someone could guide me.
It is perfectly acceptable to use both at the same time, as you said, for different purposes.
But consider, if those files are real documents and not just some data files of an internal implementation, I personally would not store any critical data about the documents separate from the documents though. Since documents from user perspective are meant to be self-sustaining - user may create, delete or move them around freely without fearing any interdependency with some other documents or objects. User expects all necessary meta-data to move with the document.
Then again if there is some "house-keeping" metadata that you can always re-create about your documents in the database, that is just fine.
I recently submitted an upgrade of my app which included a lightweight coredata migration (including new fields in existing tables and a couple of new tables). I followed every tip regarding this migration, including some I found on this site.
I thoroughly tested the update on three different devices and it all went ok!!!
However, this update is crashing an all my devices and probably on all my customers. I can't explain why this is happening.
Could you please help me understand this debacle?
To truly test your app and migration, you need to run your original app to create data store according to the original data model. Then you need to run your new app, opening data store that was generated with original app. This can be a real pain and is easier (at least initially) to do in Simulator because you have more control over the file system and can swap in a saved original data store. On iDevice you need to regenerate original data store for each test.
If you are testing on your own development devices then you have already migrated your data store. Is it possible that your test devices created their data stores with new data model - and never actually performed a migration?
I only generally use automatic migration during beta testing, for quick revisions, other than that I always use a mapping model, so that you have control.
the other issue is that if your model shifts far enough between releases, auto migration from v1-v2 could be fine, and v2-v3 could be ok, but v1-v3 could be too drastic to be inferred. by making maps for them, you retain control of the migration.