CKFetchRecordsOperation + CKQueryOperations ... what am I missing? - ios

Question

Managed to cobble together a CKFetchRecordsOperation after much searching for sample code; and here it is... but I must have missed something. Don't get me wrong it works a treat... but...
To execute a CKFetchRecordsOperation you need an NSArray of CKRecordIDs; to get a NSArray of CKRecordIDs, you need to execute CKQuery thru which you can build your NSArray of CKRecordIDs.
But wait a minute, the process of extracting the CKRecordIDs uses a CKQuery, thru which I could simply download the CKRecords anyway?
How do you get your NSArray of CKRecordIDs if not with a CKQuery?
-(void)doSingleBeaconsDownload
{
CKDatabase *publicDatabase = [[CKContainer containerWithIdentifier:#"iCloud.cqd.ch.BeaconBrowser"] publicCloudDatabase];
NSPredicate *predicatex = [NSPredicate predicateWithFormat:#"iBeaconConfig = %#",iBeaconsConfirmed.giReferenceID];
CKQuery *query = [[CKQuery alloc] initWithRecordType:#"Running" predicate:predicatex];
[self.delegate performSelectorOnMainThread:#selector(processCompleted:) withObject:#"Downloading Configuration ..." waitUntilDone:YES];
[publicDatabase performQuery:query inZoneWithID:nil completionHandler:^(NSArray *results, NSError *error) {
if (error) {
NSLog(#"Batch Download Error iCloud error %#",error);
}
else {
NSMutableArray *rex2download = [[NSMutableArray alloc] init];
for (CKRecord *rex in results) {
[rex2download addObject:rex.recordID];
}
CKFetchRecordsOperation *fetchRecordsOperation = [[CKFetchRecordsOperation alloc] initWithRecordIDs:rex2download];
/* fetchRecordsOperation.perRecordCompletionBlock = ^(CKRecord *record, CKRecordID *recordID, NSError *error) {
if (error) {
// Retain the record IDs for failed fetches
}
else {
// Do something with each record downloaded
}
};*/
fetchRecordsOperation.perRecordProgressBlock = ^(CKRecordID *record, double recordsDownloaded) {
if (error) {
// damn ...
} else {
NSLog(#"Downloaded %f", recordsDownloaded);
}
};
fetchRecordsOperation.fetchRecordsCompletionBlock = ^(NSDictionary *recordsByRecordID, NSError *error) {
if (error) {
// Failed to fetch all or some of the records
}
else {
for(CKRecord *record in results) {
NSLog(#"Fini download %lu",(unsigned long)[recordsByRecordID count]);
}
[self.delegate performSelectorOnMainThread:#selector(beaconsDownloaded:) withObject:noOf waitUntilDone:YES];
}
};
[publicDatabase addOperation:fetchRecordsOperation];
}
}];
}

Answer 1

From Apple Documentation: A CKFetchRecordsOperation object retrieves CKRecord objects (whose IDs you already know) from iCloud.
A CKQueryOperation is used to retrieve CKRecords from iCloud based on some Query, so you can get them even if you do not know their recordIDs. A CKFetchRecordsOperation is used ONLY when you have the CKRecordIDs. You can create a CKRecordID without accessing iCloud, and you can store them in any local storage you have.
A good use case, which I use for this kind of operation, is when you want to modify a CKRecord, you need to first retrieve it from iCloud (using CKFetchRecordsOperation) and then save it back using CKModifyRecordsOperation.
Have a look at the two WWDC 2014 Videos on CloudKit that explain this pretty well.

Answer 2

Thanks for your help! I managed to craft an CKQueryOperation into the code, but ... but my code is soon going be become unreadable with many more of these nested loops? Surely there is a more elegant way to link CKQuery/Fetch/Modify operations; tried dependancies but missing something still ?
-(void)doSingleBeaconsDownload
{
[self.delegate performSelectorOnMainThread:#selector(processCompleted:) withObject:#"Downloading Configuration ..." waitUntilDone:YES];
CKDatabase *publicDatabase = [[CKContainer containerWithIdentifier:#"iCloud.cqd.ch.BeaconBrowser"] publicCloudDatabase];
NSPredicate *predicatex = [NSPredicate predicateWithFormat:#"iBeaconConfig = %#",iBeaconsConfirmed.giReferenceID];
CKQuery *query = [[CKQuery alloc] initWithRecordType:#"Running" predicate:predicatex];
CKQueryOperation *queryOp =[[CKQueryOperation alloc] initWithQuery:query];
queryOp.desiredKeys = #[#"record.recordID.recordName"];
queryOp.resultsLimit = CKQueryOperationMaximumResults;
NSMutableArray *rex2download = [[NSMutableArray alloc] init];
queryOp.recordFetchedBlock = ^(CKRecord *results)
{
[rex2download addObject:results.recordID];
};
queryOp.queryCompletionBlock = ^(CKQueryCursor *cursor, NSError *error)
{
// Cursor it seems contains a reference to a second call to it [required] if you try download more then 100 records
if (error) {
NSLog(#"Batch Download Error iCloud error %#",error);
}
else {
CKFetchRecordsOperation *fetchRecordsOperation = [[CKFetchRecordsOperation alloc] initWithRecordIDs:rex2download];
fetchRecordsOperation.perRecordCompletionBlock = ^(CKRecord *record, CKRecordID *recordID, NSError *error) {
if (error) {
// Retain the record IDs for failed fetches
}
else {
// Do something ..
}
};
fetchRecordsOperation.perRecordProgressBlock = ^(CKRecordID *record, double recordsDownloaded) {
if (error) {
// damn
} else {
NSLog(#"Downloaded X");
}
};
fetchRecordsOperation.fetchRecordsCompletionBlock = ^(NSDictionary *recordsByRecordID, NSError *error) {
if (error) {
// Failed to fetch all or some of the records
}
else {
… Final clean up
}
};
[publicDatabase addOperation:fetchRecordsOperation];
}
};
[publicDatabase addOperation:queryOp];
}

Answer 3

Thanks Harry; Here is my third and final working solution; used a singleton global variable to pass the data between the two CKQueryOperations; don't know if that is best/good practice, but it works
... seems a pity you cannot use something like this ...
[fetchRecordsOperation addDependency:queryOp]; &
[queue fetchRecordsOperation]; (doesn't compile)
Would be a far cleaner solution... anyway here is V3 for completeness..
-(void)doSingleBeaconsDownloadV3
{
NSLog(#"doQuery executing");
CKDatabase *publicDatabase = [[CKContainer containerWithIdentifier:#"iCloud.cqd.ch.BeaconBrowser"] publicCloudDatabase];
NSPredicate *predicatex = [NSPredicate predicateWithFormat:#"iBeaconConfig = %#",iBeaconsConfirmed.giReferenceID];
CKQuery *query = [[CKQuery alloc] initWithRecordType:#"Running" predicate:predicatex];
CKQueryOperation *queryOp =[[CKQueryOperation alloc] initWithQuery:query];
queryOp.desiredKeys = #[#"record.recordID.recordName"];
queryOp.resultsLimit = CKQueryOperationMaximumResults;
//NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"creationDate" ascending:NO];
//query.sortDescriptors = #[sortDescriptor];
queryOp.recordFetchedBlock = ^(CKRecord *results)
{
[iBeaconsConfirmed.giRex2Download addObject:results.recordID];
NSLog(#"fetched %lu",[iBeaconsConfirmed.giRex2Download count]);
};
queryOp.queryCompletionBlock = ^(CKQueryCursor *cursor, NSError *error)
{
if (error) {
NSLog(#"Batch Download Error iCloud error %#",error);
} else {
NSLog(#"fetched %lu",[iBeaconsConfirmed.giRex2Download count]);
[self DoFetchV2];
}
};
[publicDatabase addOperation:queryOp];
}
-(void)DoFetchV2
{
NSLog(#"dofetch executing %lu",[iBeaconsConfirmed.giRex2Download count]);
CKDatabase *publicDatabase = [[CKContainer containerWithIdentifier:#"iCloud.cqd.ch.BeaconBrowser"] publicCloudDatabase];
CKFetchRecordsOperation *fetchRecordsOperation = [[CKFetchRecordsOperation alloc] initWithRecordIDs:iBeaconsConfirmed.giRex2Download];
fetchRecordsOperation.perRecordCompletionBlock = ^(CKRecord *record, CKRecordID *recordID, NSError *error) {
if (error) {
// Retain the record IDs for failed fetches
}
else {
// Do something useful with data
}
};
fetchRecordsOperation.perRecordProgressBlock = ^(CKRecordID *record, double recordsDownloaded)
{
NSLog(#"Downloaded X");
};
fetchRecordsOperation.fetchRecordsCompletionBlock = ^(NSDictionary *recordsByRecordID, NSError *error) {
if (error) {
// Failed to fetch all or some of the records
} else {
NSLog(#"Fini download %lu",(unsigned long)[recordsByRecordID count]);
}
};
[publicDatabase addOperation:fetchRecordsOperation];
}