YDBCKMergeInfo

@interface YDBCKMergeInfo : NSObject

This utility class is used by the YapDatabaseCloudKitMergeBlock.

  • Apple’s CloudKit framework does NOT tell us which properties of a CKRecord were remotely changed. That is, when we fetch CKRecords that have been changed by a different device, we are only given:

    • The CKRecord that was changed
    • The most recent key/value pairs for the CKRecord (all key value pairs, even those that didn’t change)

    This becomes problematic when we are tasked with performing a merge. For example:

    • We change contact.firstName property
    • We attempt to upload the corresponding CKRecord
    • CloudKit gives us an error - record is out-of-date (changed remotely)
    • We then pull down the latest version of the CKRecord
    • And we are now tasked with merging this version with our version

    The big question is: Did the remote device change the firstName property ???

    Unfortunately, this is not possible to answer this question with only the following information:

    • The latest version of the CKRecord from the server
    • The latest version of the CKRecord locally (pending upload)
    • The list of properties that were changed locally (pending upload)

    There is one critical piece of information that is missing:

    • The original values for the properties that were changed locally

    With this critical piece of information in hand, we can:

    • Enumerate the key/value pairs of the CKRecord from the server
    • Compare each value with our own local value
    • If they match, then we don’t have any problems
    • If they don’t match, and we didn’t change the value locally, then we can simply accept the new value from remote
    • If they don’t match, and we did change the value locally:
      • If the remote value matches our original value, then the remote device didn’t change the value, and we can keep our local change.
      • If the remote value doesn’t match our original value, then we have a conflict, and we’ll need to choose which value to keep. (generally remote wins)

    So how do we go about storing the originalValues ? YapDatabaseCloudKit will store it for you if you provide the info via the recordBlock. That is, the recordBlock has a YDBCKRecordInfo parameter. And YDBCKRecordInfo has an originalValues property that you can set. If you set this, then YapDatabaseCloudKit will handle everything else for you.

    See MyDatabaseObject for an example of how you might use KVO to track originalValue(s). See CloudKitTodo sample project for a complete Xcode project example.

    Declaration

    Objective-C

    @property (readonly, strong, nonatomic)
    NSDictionary<NSString *, id> *_Nonnull originalValues;

    Swift

    var originalValues: [String : Any] { get }

  • Declaration

    Objective-C

    @property (readonly, strong, nonatomic, nullable) CKRecord *pendingLocalRecord;

    Swift

    var pendingLocalRecord: CKRecord? { get }

  • Declaration

    Objective-C

    @property (readonly, strong, nonatomic)
    CKRecord *_Nonnull updatedPendingLocalRecord;

    Swift

    var updatedPendingLocalRecord: CKRecord { get }