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我正在使用 CloudKit 从使用 CKQuery 的私有数据库中检索记录，在异步函数中使用 CKQueryOperation.queryResultBlock。我已经找到了几个使用 queryCompletionBlock 的示例，但这些示例已被弃用并被 queryResultBlock 取代，关于如何实现它的可用文档很少。只要不返回查询完成游标（<=100 条记录），我的函数就可以很好地工作，但我无法弄清楚如何迭代它。

这是我正在使用的代码：

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)
    }
}

我试图实现类似示例中的代码但没有成功：上面的代码导致致命错误“SWIFT TASK CONTINUATION MISUSE”作为该行

continuation.resume(returning: resultRecords)

显然被多次调用（非法）。用“// for > 100 records”注释的行代表我添加到迭代的代码；其他一切都适用于 100 或更少的记录集。

我是否需要迭代地调用 queryRecords 函数本身，如果它存在则传递查询游标，或者是否可以像我在这里尝试做的那样将迭代操作添加到队列中？

如果有人在使用 queryResultBlock（不推荐使用 queryCompletionBlock）之前这样做过，请帮忙！谢谢！

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1 回答 1

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queryResultBlock在 Swift 5.5 中不需要。

我使用它是因为我的CKRecord类型总是与它们的 Swift 对应物命名相同。如果你愿意，你可以recordType: "\(Record.self)"用你的recordType来代替。

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: [], +=)
    }
  }
}
于 2022-02-21T00:56:57.180 回答