Swift CloudKit 和CKQuery：当queryResultBlock returns 查询游标时如何迭代检索记录

Question

我正在使用 CloudKit 使用 CKQuery 从私有数据库检索记录，在异步函数中使用 CKQueryOperation.queryResultBlock。我已经找到了几个使用 queryCompletionBlock 的例子，但它已被弃用并被 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），我的函数就可以正常工作，但我不知道如何迭代它。

这是我使用的代码：

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)
    }
}

我试图从类似的示例中实现代码，但没有成功：上面的代码导致致命错误“SWIFT TASK CONTINUATION MISUSE”作为行

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中的代码；其他一切都适用于 100 或更少的记录集。

我是否需要迭代调用 queryRecords 函数本身，传递查询游标（如果存在），或者是否可以像我在这里尝试的那样将迭代操作添加到队列中？

如果有人在使用 queryResultBlock（未弃用 queryCompletionBlock）之前做过此操作，请帮忙！谢谢！

Answer 1

在 Swift 5.5 中不需要 queryResultBlock。

我使用它是因为我的 CKRecord 类型总是与它们的 Swift 类型命名相同。如果需要，您可以将 recordType: "\(Record.self)" 替换为 recordType。

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,
    zoneID: CKRecordZone.ID? = nil,
    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 .get() }
        }
        
        if let cursor = records.queryCursor {
          try await process(self.records(continuingMatchFrom: cursor))
        }
      }

      try await process(
        records(
          matching: .init(
            recordType: "\(Record.self)",
            predicate: predicate
          ),
          inZoneWith: zoneID
        )
      )
      
      return try await group.reduce(into: [], +=)
    }
  }
}

Answer 2

这是我根据 Jessy 的回复修改的代码，我在其中添加了 CKRecordZone.ID 参数，以便将查询限制在特定的记录区域。该函数还允许从 public 或私有数据库查询，其中 public 数据库必须仅使用默认区域。

public func queryRecords(recordType: CKRecord.RecordType, predicate: NSPredicate, publicDB: Bool) async throws -> [CKRecord] {
            let db = publicDB ? container.publicCloudDatabase : container.privateCloudDatabase
            let zoneID = publicDB ? CKRecordZone.default().zoneID : zoneID
            return try await db.records(type: recordType, predicate: predicate, zoneID: zoneID)
        }

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(
    type: CKRecord.RecordType,
    predicate: NSPredicate = .init(value: true),
    zoneID: CKRecordZone.ID
  ) 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 .get() }
        }
        if let cursor = records.queryCursor {
          try await process(self.records(continuingMatchFrom: cursor))
        }
      }
      try await process(
        records(
          matching: .init(
            recordType: type,
            predicate: predicate
          ),
          inZoneWith: zoneID
        )
      )
        
        return try await group.reduce(into: [], +=)
      }
    }
}

Swift CloudKit 和CKQuery：当queryResultBlock returns 查询游标时如何迭代检索记录

Swift CloudKit and CKQuery: how to iteratively retrieve records when queryResultBlock returns a query cursor

swift

asynchronous

cloudkit

ckquery