# CloudKit and Core Data

* Core Data and CloudKit are conceptually similar but implemented in very different ways.
* You can now check a use CloudKit checkbox when you add Core Data to your app.
* You need to add the iCloud and Background mode capabilities yourself in order to use CloudKit and update your app in the background.
* Xcode creates a container identifier for your app.
* `NSPersistentCloudKitContainer` managed persistent stores that sync data too iCloud. The CloudKit container is a subclass of the `NSPersistentContainer`.
* The CloudKit container contains all the boilerplate code that you would normally have to write yourself.
* Apple asks for feedback on this container explicitly.
* CloudKit container creates a local replica of the CloudKit store.
* You can add separate stores for cloud and non-cloud synced entities. You can use persistent store descriptions to tell the container which stores it manages.
* A persistent CloudKit container can share data across multiple applications by creating a shared sqlite file.
* The container understands how to optimize certain CloudKit storage aspects, for instance, it's able to use either an asset or plain string to store text of variable length.
* One to many relationships do not use ckreference because there is a limit of 750 references for an item. Instead they use UUIDs so they have unlimited references.
* Many to many relationships are implemented through a linking table.
* When modeling for collaboration and you have a textfield, you might want to use a to many relationship for the textfield content so conflicts can't happen (as easily).

Worth watching, documentation is updated.