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我正在努力理解如何批量保存获取的对象并将它们存储到数据库中。将对象存储到数据库后，我想返回查询结果。我无法理解如何使用 EventLoopF​​uture 执行此操作，因为当我打电话时.wait()收到错误消息：

前提条件失败：检测到错误：在 EventLoop 上时不得调用 wait()。

作为我的问题的一个例子：

  • 我需要从外部端点获取一个实体（比如说机场的航班）
  • 该调用的结果需要保存到数据库中。如果航班存在于数据库中，则需要更新，否则创建。
  • 完成后，需要返回数据库中所有航班的列表。

这是我到目前为止得到的，但这给了我一个错误：

func flights(on conn: DatabaseConnectable, customerName: String, flightType: FlightType) throws -> Future<[Flight]> {

    return Airport.query(on: conn).filter(\.customerName == customerName).first().flatMap(to: [Flight].self) { airport in
      guard let airport = airport else {
        throw Abort(.notFound)
      }

      guard let airportId = airport.id else {
        throw Abort(.internalServerError)
      }

      // Update items for customer
      let fetcher: AirportManaging?

      switch customerName.lowercased() {
      case "coolCustomer":
        fetcher = StoreOneFetcher()
      default:
        fetcher = nil
        debugPrint("Unhandled customer to fetch from!")
        // Do nothing
      }

      let completion = Flight.query(on: conn).filter(\.airportId == airportId).filter(\.flightType == flightType).all

      guard let flightFetcher = fetcher else { // No customer fetcher to get from, but still return whats in the DB
        return completion()
      }

      return try flightFetcher.fetchDataForAirport(customerName, on: conn).then({ (flights) -> EventLoopFuture<[Flight]> in
        flights.forEach { flight in
          _ = try? self.storeOrUpdateFlightRecord(flight, airport: airport, on: conn).wait()
        }
        return completion()
      })
    }
  }

  func storeOrUpdateFlightRecord(_ flight: FetcherFlight, airport: Airport, on conn: DatabaseConnectable) throws -> EventLoopFuture<Flight> {
    guard let airportId = airport.id else {
      throw Abort(.internalServerError)
    }

    return Flight.query(on: conn).filter(\.itemName == flight.itemName).filter(\.airportId == airportId).filter(\.flightType == flight.type).all().flatMap(to: Flight.self) { flights in
      if let firstFlight = flights.first {
        debugPrint("Found flight in database, updating...")
        return flight.toFlight(forAirport: airport).save(on: conn)
      }

      debugPrint("Did not find flight, saving new...")
      return flight.toFlight(forAirport: airport).save(on: conn)
    }
  }

所以问题就在网上_ = try? self.storeOrUpdateFlightRecord(flight, airport: airport, on: conn).wait()。我不能打电话wait()，因为它会阻止 eventLoop，但是如果我打电话map或者flatMap我需要反过来返回一个EventLoopFuture<U>( Ubeing Flight)，我对此完全不感兴趣。

我想self.storeOrUpdateFlightRecord被叫到结果被忽略。我怎样才能做到这一点？

4

1 回答 1

8

是的，你不能使用.wait()on eventLoop。

在您的情况下，您可以flatten用于批处理操作

/// Flatten works on array of Future<Void>
return flights.map {
    try self.storeOrUpdateFlightRecord($0, airport: airport, on: conn)
        /// so transform a result of a future to Void
        .transform(to: ())
}
/// then run flatten, it will return Future<Void> as well
.flatten(on: conn).flatMap {
    /// then do what you want :)
    return completion()
}
于 2019-02-26T22:18:30.803 回答