Swift/CloudKit : After record changed, 上传触发器 "Service Record Changed"

Question

我正在尝试将 CKReference 添加到云工具包中的记录，但尝试不断触发“服务记录已更改”。从我的 println 显示的控制台消息(下面的控制台消息和代码), 我正在上传带有 0 个引用的记录，然后当我附加引用时，我看到尝试上传带有 1 个引用的记录。然后我收到错误。

据我所知，不应触发“服务记录已更改”，因为引用列表中的值已更改(记录有一个完整的额外字段)。即使我在开发模式，我手动为Reference List创建了key-value字段，因为当reference list为空时，第一次上传的记录不包括该字段(上传空数组会导致另一个错误)。

我将在控制台消息之后按照相关性顺序包含代码(您将能够看到大部分 println)。整个项目都在 github 上，如果需要，我可以链接到它或包含更多代码。

相关控制台:

name was set
uploading TestCrewParticipant
with 0 references
if let projects
upload succeeded: TestCrewParticipant
attaching reference
adding TestVoyage:_d147aa657fbf2adda0c82bf30d0e29a9 from guard
references #: Optional(1)
uploading TestCrewParticipant
with 1 references
if let projects
success: 1
uploading TestCrewParticipant
with 1 references
if let projects
success: 1
local storage tested: TestCrewParticipant
u!error for TestCrewParticipant
CKError: <CKError 0x7fcbd05fa960: "Server Record Changed" (14/2004); server message = "record to insert already exists"; uuid = 96377029-341E-487C-85C3-E18ADE1119DF; container ID = "iCloud.com.lingotech.cloudVoyageDataModel">
u!error for TestCrewParticipant
CKError: <CKError 0x7fcbd05afb80: "Server Record Changed" (14/2004); server message = "record to insert already exists"; uuid = 3EEDE4EC-4BC1-4F18-9612-4E2C8A36C68F; container ID = "iCloud.com.lingotech.cloudVoyageDataModel">
passing the guard 

来自 CrewParticipant 的代码:

/**
 * This array stores a conforming instance's CKReferences used as database
 * relationships. Instance is owned by each record that is referenced in the
 * array (supports multiple ownership)
 */
var references: [CKReference] { return associatedProjects ?? [CKReference]() }

// MARK: - Functions

/**
 * This method is used to store new ownership relationship in references array,
 * and to ensure that cloud data model reflects such changes. If necessary, ensures
 * that owned instance has only a single reference in its list of references.
 */
mutating func attachReference(reference: CKReference, database: CKDatabase) {
print("attaching reference")
    guard associatedProjects != nil else {
print("adding \(reference.recordID.recordName) from guard")
        associatedProjects = [reference]
        uploadToCloud(database)
        return
    }
print("associatedProjects: \(associatedProjects?.count)")
    if !associatedProjects!.contains(reference) {
print("adding \(reference.recordID.recordName) regularly")
        associatedProjects!.append(reference)
        uploadToCloud(database)
    }
}

/**
 * An identifier used to store and recover conforming instances record.
 */
var recordID: CKRecordID { return CKRecordID(recordName: identifier) }

/**
 * This computed property generates a conforming instance's CKRecord (a key-value
 * cloud database entry). Any values that conforming instance needs stored should be
 * added to the record before returning from getter, and conversely should recover
 * in the setter.
 */
var record: CKRecord {
    get {
        let record = CKRecord(recordType: CrewParticipant.REC_TYPE, recordID: recordID)

        if let id = cloudIdentity { record[CrewParticipant.TOKEN] = id }

// There are several other records that are dealt with successfully here.

print("if let projects")
        // Referable properties
        if let projects = associatedProjects {
print("success: \(projects.count)")
            record[CrewParticipant.REFERENCES] = projects
        }

        return record
    }

    set { matchFromRecord(newValue) }
}

发生上传的通用代码(适用于其他几个类):

/**
 * This method uploads any instance that conforms to recordable up to the cloud. Does not check any 
 * redundancies or for any constraints before (over)writing.
 */
func uploadRecordable<T: Recordable>
    (instanceConformingToRecordable: T, database: CKDatabase, completionHandler: (() -> ())? = nil) {
print("uploading \(instanceConformingToRecordable.recordID.recordName)")
if let referable = instanceConformingToRecordable as? Referable { print("with \(referable.references.count) references") }
    database.saveRecord(instanceConformingToRecordable.record) { record, error in
        guard error == nil else {
print("u!error for \(instanceConformingToRecordable.recordID.recordName)")
            self.tempHandler = { self.uploadRecordable(instanceConformingToRecordable,
                                                       database: database,
                                                       completionHandler: completionHandler) }
            CloudErrorHandling.handleError(error!, errorMethodSelector: #selector(self.runTempHandler))
            return
        }
print("upload succeeded: \(record!.recordID.recordName)")
        if let handler = completionHandler { handler() }
    }
}

/**
 * This method comprehensiviley handles any cloud errors that could occur while in operation.
 *
 * error: NSError, not optional to force check for nil / check for success before calling method.
 *
 * errorMethodSelector: Selector that points to the func calling method in case a retry attempt is
 * warranted. If left nil, no retries will be attempted, regardless of error type.
 */
static func handleError(error: NSError, errorMethodSelector: Selector? = nil) {

    if let code: CKErrorCode = CKErrorCode(rawValue: error.code) {
        switch code {

        // This case requires a message to USER (with USER action to resolve), and retry attempt.
        case .NotAuthenticated:
            dealWithAuthenticationError(error, errorMethodSelector: errorMethodSelector)

        // These cases require retry attempts, but without error messages or USER actions.
        case .NetworkUnavailable, .NetworkFailure, .ServiceUnavailable, .RequestRateLimited, .ZoneBusy, .ResultsTruncated:
            guard errorMethodSelector != nil else { print("Error Retry CANCELED: no selector"); return }
            retryAfterError(error, selector: errorMethodSelector!)

        // These cases require no message to USER or retry attempts.
        default:
            print("CKError: \(error)")
        }            
    }
}

Answer 1

看起来您每次保存时都在创建一个新的 CKRecord。

CloudKit 正在返回 ServerRecordChanged 以告诉您服务器上已存在具有相同 recordID 的记录，并且您尝试保存被拒绝，因为服务器记录的版本不同。

Each record has a change tag that allows the server to track when that record was saved. When you save a record, CloudKit compares the change tag in your local copy of the record with the one on the server. If the two tags do not match—meaning that there is a potential conflict—the server uses the value in the [savePolicy property of CKModifyRecordsOperation] to determine how to proceed.

来源: CKModifyRecordsOperation Reference

尽管您使用的是 CKDatabase.saveRecord 便捷方法，但这仍然适用。默认的保存策略是 ifServerRecordUnchanged。

首先，我建议过渡到 CKModifyRecordsOperation，尤其是当您要保存多条记录时。它使您可以更好地控制流程。

其次，在保存对现有记录的更改时，您需要从服务器对 CKRecord 进行更改。您可以通过以下任一方式完成此操作:

1. 从 CloudKit 请求 CKRecord，对该 CKRecord 进行更改，然后将其保存回 CloudKit。
2. 使用 CKRecord Reference 中的建议存储已保存的 CKRecord(保存后在完成 block 中返回的那个) ，保留此数据，然后将其解档以取回 CKRecord，您可以对其进行修改并保存到服务器。 (这避免了一些请求服务器 CKRecord 的网络往返。)

Storing Records Locally

If you store records in a local database, use the encodeSystemFields(with:) method to encode and store the record’s metadata. The metadata contains the record ID and change tag which is needed later to sync records in a local database with those stored by CloudKit.

let record = ...

// archive CKRecord to NSData
let archivedData = NSMutableData()
let archiver = NSKeyedArchiver(forWritingWithMutableData: archivedData)
archiver.requiresSecureCoding = true
record.encodeSystemFieldsWithCoder(archiver)
archiver.finishEncoding()

// unarchive CKRecord from NSData
let unarchiver = NSKeyedUnarchiver(forReadingWithData: archivedData)  
unarchiver.requiresSecureCoding = true 
let unarchivedRecord = CKRecord(coder: unarchiver)

来源: CloudKit Tips and Tricks - WWDC 2015

请记住:如果另一台设备在您请求/上次保存并存储服务器记录后保存对记录的更改，您仍然会遇到 ServerRecordChanged 错误。您需要通过获取最新的服务器记录并将您的更改重新应用到该 CKRecord 来处理此错误。