CloudKit - 具有依赖项的 CKQueryOperation

我刚刚开始使用 CloudKit，所以请耐心等待。

背景信息

苹果在 WWDC 2015 上发表了有关 CloudKit 的演讲https://developer.apple.com/videos/wwdc/2015/?id=715 https://developer.apple.com/videos/wwdc/2015/?id=715

在本次演讲中，他们警告不要创建链接查询，而是推荐这种策略：

let firstFetch = CKFetchRecordsOperation(...)
let secondFetch = CKFetchRecordsOperation(...)
...
secondFetch.addDependency(firstFetch)

letQueue = NSOperationQueue()
queue.addOperations([firstFetch, secondFetch], waitUntilFinished: false)

结构示例

测试项目数据库包含宠物及其主人，如下所示：

|Pets               |   |Owners     |
|-name              |   |-firstName |
|-birthdate         |   |-lastName  |
|-owner (Reference) |   |           |

我的问题

我正在尝试找到属于某个主人的所有宠物，并且我担心我正在创建苹果警告的连锁店。请参阅下面的两种方法，它们执行相同的操作，但有两种方式。哪个更正确，或者两者都是错误的？我觉得我在做同样的事情，但只是使用完成块。

我对如何更改 otherSearchBtnClick: 以使用依赖项感到困惑。我需要在哪里添加

ownerQueryOp.addDependency(queryOp)

在其他SearchBtn中点击：？

@IBAction func searchBtnClick(sender: AnyObject) {
    var petString = ""
    let container = CKContainer.defaultContainer()
    let publicDatabase = container.publicCloudDatabase
    let privateDatabase = container.privateCloudDatabase

    let predicate = NSPredicate(format: "lastName == '\(ownerLastNameTxt.text)'")
    let ckQuery = CKQuery(recordType: "Owner", predicate: predicate)
    publicDatabase.performQuery(ckQuery, inZoneWithID: nil) {
        record, error in
        if error != nil {
            println(error.localizedDescription)
        } else {
            if record != nil {
                for owner in record {
                    let myRecord = owner as! CKRecord
                    let myReference = CKReference(record: myRecord, action: CKReferenceAction.None)

                    let myPredicate = NSPredicate(format: "owner == %@", myReference)
                    let petQuery = CKQuery(recordType: "Pet", predicate: myPredicate)
                    publicDatabase.performQuery(petQuery, inZoneWithID: nil) {
                        record, error in
                        if error != nil {
                            println(error.localizedDescription)
                        } else {
                            if record != nil {
                                for pet in record {
                                    println(pet.objectForKey("name") as! String)

                                }

                            }
                        }
                    }
                }
            }
        }
    }
}

@IBAction func otherSearchBtnClick (sender: AnyObject) {
    let container = CKContainer.defaultContainer()
    let publicDatabase = container.publicCloudDatabase
    let privateDatabase = container.privateCloudDatabase

    let queue = NSOperationQueue()
    let petPredicate = NSPredicate(format: "lastName == '\(ownerLastNameTxt.text)'")
    let petQuery = CKQuery(recordType: "Owner", predicate: petPredicate)
    let queryOp = CKQueryOperation(query: petQuery)
    queryOp.recordFetchedBlock = { (record: CKRecord!) in
        println("recordFetchedBlock: \(record)")
        self.matchingOwners.append(record)
    }

    queryOp.queryCompletionBlock = { (cursor: CKQueryCursor!, error: NSError!) in
        if error != nil {
            println(error.localizedDescription)
        } else {
            println("queryCompletionBlock: \(cursor)")
            println("ALL RECORDS ARE: \(self.matchingOwners)")
            for owner in self.matchingOwners {
                let ownerReference = CKReference(record: owner, action: CKReferenceAction.None)
                let ownerPredicate = NSPredicate(format: "owner == %@", ownerReference)
                let ownerQuery = CKQuery(recordType: "Pet", predicate: ownerPredicate)
                let ownerQueryOp =  CKQueryOperation(query: ownerQuery)
                ownerQueryOp.recordFetchedBlock = { (record: CKRecord!) in
                    println("recordFetchedBlock (pet values): \(record)")
                    self.matchingPets.append(record)
                }
                ownerQueryOp.queryCompletionBlock = { (cursor: CKQueryCursor!, error: NSError!) in
                    if error != nil {
                        println(error.localizedDescription)
                    } else {
                        println("queryCompletionBlock (pet values)")
                        for pet in self.matchingPets {
                            println(pet.objectForKey("name") as! String)
                        }
                    }
                }
            publicDatabase.addOperation(ownerQueryOp)
            }
        }


    }
    publicDatabase.addOperation(queryOp)
}

如果您不需要取消并且不担心在网络错误上重试，那么我认为您可以很好地链接查询。

我知道我知道，在 WWDC 2015 中，Nihar Sharma 推荐了添加依赖项方法，但看起来他只是在最后没有考虑太多就将其添加了。您会看到不可能重试 NSOperation，因为它们无论如何都是一次性的，并且他没有提供取消队列中已有操作的示例，也没有提供如何从一个操作传递数据到下一个操作的示例。鉴于这 3 个复杂问题可能需要数周时间才能解决，请坚持现有工作，等待下届 WWDC 的解决方案。另外，块的全部意义在于让您调用内联方法并能够访问上述方法中的参数，因此如果您转向操作，您就无法充分利用该优势。

他不使用链接的主要原因是荒谬的，他无法分辨哪个错误是针对哪个请求的，他将他的错误命名为 someError 然后 otherError 等。没有一个头脑正常的人会在块内命名不同的错误参数，所以只需使用所有这些都具有相同的名称，然后您就知道在一个块内您始终使用正确的错误。因此，他是创建混乱场景并为其提供解决方案的人，但是最好的解决方案是首先不要创建多个错误参数名称的混乱场景！

话虽如此，如果您仍然想尝试使用操作依赖项，这里有一个示例说明如何完成此操作：

__block CKRecord* venueRecord;
CKRecordID* venueRecordID = [[CKRecordID alloc] initWithRecordName:@"4c31ee5416adc9282343c19c"];
CKFetchRecordsOperation* fetchVenue = [[CKFetchRecordsOperation alloc] initWithRecordIDs:@[venueRecordID]];
fetchVenue.database = [CKContainer defaultContainer].publicCloudDatabase;

// init a fetch for the category, it's just a placeholder just now to go in the operation queue and will be configured once we have the venue.
CKFetchRecordsOperation* fetchCategory = [[CKFetchRecordsOperation alloc] init];

[fetchVenue setFetchRecordsCompletionBlock:^(NSDictionary<CKRecordID *,CKRecord *> * _Nullable recordsByRecordID, NSError * _Nullable error) {
    venueRecord = recordsByRecordID.allValues.firstObject;
    CKReference* ref = [venueRecord valueForKey:@"category"];

    // configure the category fetch
    fetchCategory.recordIDs = @[ref.recordID];
    fetchCategory.database = [CKContainer defaultContainer].publicCloudDatabase;
}];

[fetchCategory setFetchRecordsCompletionBlock:^(NSDictionary<CKRecordID *,CKRecord *> * _Nullable recordsByRecordID, NSError * _Nullable error) {
    CKRecord* categoryRecord = recordsByRecordID.allValues.firstObject;

    // here we have a venue and a category so we could call a completion handler with both.
}];

NSOperationQueue* queue = [[NSOperationQueue alloc] init];
[fetchCategory addDependency:fetchVenue];
[queue addOperations:@[fetchVenue, fetchCategory] waitUntilFinished:NO];

它的工作原理是首先获取 Venue 记录，然后获取其类别。

抱歉，没有错误处理，但正如您所看到的，已经有大量代码可以通过链接在几行中完成某些操作。就我个人而言，我发现这个结果比简单地将便捷方法链接在一起更复杂和令人困惑。