Get partial errors from NSError - ios

Question

When using CloudKit, sometimes the error returned is PartialFailure, which may caused by duplicate subscriptions, etc. See example below.
<CKError 0x7f8318711520: "Partial Failure" (2/1011);
"Failed to modify some subscriptions"; uuid = A434B010-7650-4BBA-8A7A-33CD0690FD15;
container ID = "iCloud.xxx.xxx"; partial errors: {
EFC65F4A-A595-44A3-A022-323D9CE9B535 = <CKError 0x7f831a007be0: "Server Rejected Request" (15/2032); server message = "subscription is duplicate of '_930081460_AA87A676-DE57-4530-8BB8-7465BF4F4303'">
C4913907-28F3-42DB-8455-9966D9084834 = <CKError 0x7f83185cfc20: "Server Rejected Request" (15/2032); server message = "subscription is duplicate of '_930081460_F92FA91D-3E92-4E46-AE59-E912F8871026'"> }>
I wish to retrieve these partial errors from the main error object but I don't know how. NSError doesn't have a partialError property, and it neither has a key in userInfo to retrieve that.

Answer 1

You aren't getting back a straight NSError, you are getting back a CKError. Looking at the documentation for CKError, there is in fact a CKPartialErrorsByItemIDKey key. That looks like the key that would return a dictionary of CKErrors keyed by item ID if you ask me! The userInfo object should contain that key.
Also documented here
CloudKit Framework Constants Reference

Answer 2

Two years later, and I still don't think how to access partial errors is particularly well documented. Thanks to #Acey for putting me on the right path with CKPartialErrorsByItemIDKey
For those who are struggling, here is an example of how I ended up accessing a partial error in a CKModifySubscriptionsOperation (Swift 2.2):
someZoneSubscriptionOperation.modifySubscriptionsCompletionBlock = {(savedSubscriptions: [CKSubscription]?, deletedSubscriptionIDs:[String]?, operationError:NSError?) in
// check specifically for an error in changing subscriptions to custom zone with specific subscriptionID
if let partialError = operationError?.userInfo[CKPartialErrorsByItemIDKey]?[subscriptionID] as? ErrorType {
print(partialError) // prints partial error for custom zone with `subscriptionID` if it exists
}
}