Vapor 3：使用wait（）时检测到Eventloop错误

Question

我正在努力了解如何执行对已获取对象的批量保存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，因为当我调用.wait()时，我收到错误消息：

前提条件失败：BUG DETECTED：在EventLoop上不能调用wait（）。

作为我的问题的一个例子：

• 我需要从外部端点获取实体（假设是机场的航班）
• 该调用的结果需要保存到数据库中。如果数据库中存在航班，则需要以其他方式更新。
• 完成后，需要返回数据库中所有航班的列表。

这是我到目前为止所得到的，但它给了我错误：

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)
    }
  }

所以在线_ = try? self.storeOrUpdateFlightRecord(flight, airport: airport, on: conn).wait()的问题。我不能打电话给wait()，因为它会阻止eventLoop，但如果我打电话给map或flatMap我需要反过来返回EventLoopFuture<U>（U是Flight），我完全不感兴趣。

我希望调用self.storeOrUpdateFlightRecord并忽略结果。我怎样才能做到这一点？

Answer 1

是的，你不能在.wait()上使用eventLoop。

在您的情况下，您可以使用flatten进行批处理操作

/// 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()
}