Saving An Array Of Objects In CloudKit

Question

I'm confused about how to best save an object that contains an array of other objects in CloudKit.

Say I have a todo list app, which has different collections of items. How would I go about saving/fetching a whole collection of items?

Would I have a Record type of Collection, which would have a String Attribute called "Name", and then a Reference List Attribute called "Items"?

I know that the Record type of Item needs to have a Reference Attribute called "Collection", because of how CloudKit references from a child object to its parent.

I have managed to save a Collection without any instances of Item with the following code

func addCollection(collection: Collection!, completion: (error: NSError!) -> ()) {
    if collection == nil
        return
    }
    let collectionRecord = CKRecord(recordType: "Collection")
    CollectionRecord.setObject(collection.name, forKey: "Name")
    privateDB.saveRecord(collectionRecord) {
        record, error in
        dispatch_async(dispatch_get_main_queue()) {
           completion(error: error)
        }
    }
}

The other option is when saving a Collection, to loop through all instances of Item and also save those individually, their Reference Attribute to Collection making the connection on the CloudKit side, but this seems like way too many network calls.

Answer 1

For the Item records you need a CKReference to the Collection. You will then be able to set a CKReferenceAction on that. You don't need to create a CKReference list on the Collection.

Having a list of CKReference objects is only an option when you are planning to use CKReferenceAction.None Which would mean that there is not a strict relation between the two recordTypes

If you have a Collection object, then you can easily query the Item recordType using a predicate that Checks if the CKReference is that of the Collection.

Usually there is no need to save multiple records. Once you have created a Collection with Items the relation can remain unchanged. If you do need to change multiple records, then you could try using the CKModifyRecordsOperation which has support for saving multiple items in one action.

When linking existing Item recordTypes to a Collection, you do need to save each Item because it has a CKReference to the Collecion. The Item has changed, so it must be saved.