SwiftCloudKit和CKQuery：如何在queryResultBlock回傳查詢游標時迭代檢索記錄

我正在使用 CloudKit 從使用 CKQuery 的私有資料庫中檢索記錄，在異步函式中使用 CKQueryOperation.queryResultBlock。我已經找到了幾個使用 queryCompletionBlock 的示例，但這些示例已被棄用并被 queryResultBlock 取代，關于如何實作它的可用檔案很少。只要不回傳查詢完成游標（<=100 條記錄），我的函式就可以很好地作業，但我無法弄清楚如何迭代它。

這是我正在使用的代碼：

public func queryRecords(recordType: CKRecord.RecordType, predicate: NSPredicate) async throws -> [CKRecord] {
    var resultRecords: [CKRecord] = []
    let db = container.privateCloudDatabase
    let query = CKQuery(recordType: recordType, predicate: predicate)
    let operation = CKQueryOperation(query: query)
    let operationQueue = OperationQueue() // for > 100 records
    operationQueue.maxConcurrentOperationCount = 1 // for > 100 records
    operation.zoneID = zoneID
    debugPrint("query for recordType=\(recordType) in zone \(zoneID.zoneName) with predicate \(predicate)")
    return try await withCheckedThrowingContinuation { continuation in
        operation.queryResultBlock = { result in
            switch result {
            case .failure(let error):
                debugPrint(error)
                continuation.resume(throwing: error)
            case .success(let ckquerycursor):
                debugPrint("successful query completion after \(resultRecords.count) record(s) returned")
                if let ckquerycursor = ckquerycursor {
                    debugPrint("***** received a query cursor, need to fetch another batch! *****")
                    let newOperation = CKQueryOperation(cursor: ckquerycursor)  // for > 100 records
                    newOperation.queryResultBlock = operation.queryResultBlock // for > 100 records
                    newOperation.database = db // for > 100 records
                    operationQueue.addOperation(newOperation) // for > 100 records
                }
                continuation.resume(returning: resultRecords)
            }
        }
        operation.recordMatchedBlock = { (recordID, result1) in
            switch result1 {
            case .failure(let error):
                debugPrint(error)
            case .success(let ckrecord):
                resultRecords.append(ckrecord)
            }
        }
        db.add(operation)
    }
}

我試圖實作類似示例中的代碼但沒有成功：上面的代碼導致致命錯誤“SWIFT TASK CONTINUATION MISUSE”作為該行

continuation.resume(returning: resultRecords)

顯然被多次呼叫（非法）。用“// for > 100 records”注釋的行代表我添加到迭代的代碼；其他一切都適用于 100 或更少的記錄集。

我是否需要迭代地呼叫 queryRecords 函式本身，如果它存在則傳遞查詢游標，或者是否可以像我在這里嘗試做的那樣將迭代操作添加到佇列中？

如果有人在使用 queryResultBlock（不推薦使用 queryCompletionBlock）之前這樣做過，請幫忙！謝謝！

uj5u.com熱心網友回復：

queryResultBlock在 Swift 5.5 中不需要。

我使用它是因為我的CKRecord型別總是與它們的 Swift 對應物命名相同。如果你愿意，你可以recordType: "\(Record.self)"用你的recordType來代替。

public extension CKDatabase {
  /// Request `CKRecord`s that correspond to a Swift type.
  ///
  /// - Parameters:
  ///   - recordType: Its name has to be the same in your code, and in CloudKit.
  ///   - predicate: for the `CKQuery`
  func records<Record>(
    type _: Record.Type,
    predicate: NSPredicate = .init(value: true)
  ) async throws -> [CKRecord] {
    try await withThrowingTaskGroup(of: [CKRecord].self) { group in
      func process(
        _ records: (
          matchResults: [(CKRecord.ID, Result<CKRecord, Error>)],
          queryCursor: CKQueryOperation.Cursor?
        )
      ) async throws {
        group.addTask {
          try records.matchResults.map { try $1.get() }
        }
        
        if let cursor = records.queryCursor {
          try await process(self.records(continuingMatchFrom: cursor))
        }
      }
      
      try await process(
        records(
          matching: .init(
            recordType: "\(Record.self)",
            predicate: predicate
          )
        )
      )
      
      return try await group.reduce(into: [],  =)
    }
  }
}

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