Vapor 3：使用 wait() 时检测到 Eventloop 错误

Question

我正在努力理解如何对获取的对象执行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 return 查询结果。我无法理解如何使用 EventLoopFuture 执行此操作，因为当我调用 .wait() 时收到错误消息：

Precondition failed: BUG DETECTED: wait() must not be called when on an EventLoop.

以我的问题为例：

我需要从外部端点获取实体（比方说机场的航班）
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return编辑数据库中所有航班的列表。

这是我到目前为止得到的结果，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)
    }
  }

所以问题在线_ = try? self.storeOrUpdateFlightRecord(flight, airport: airport, on: conn).wait()。我不能调用 wait() 因为它会阻塞 eventLoop 但如果我调用 map 或 flatMap 我又需要 return 一个 EventLoopFuture<U> (U 是 Flight)，我对此完全不感兴趣。

我希望调用 self.storeOrUpdateFlightRecord 并忽略结果。我该怎么做？

Answer 1

是的，你不能在 eventLoop 上使用 .wait()。

在您的情况下，您可以使用 flatten 进行批量操作

/// Flatten works on array of Future<Void>
return flights.map {
    try self.storeOrUpdateFlightRecord([=10=], 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()
}

Vapor 3：使用 wait() 时检测到 Eventloop 错误

Vapor 3: Eventloop bug detected when using wait()

future

event-loop

swift

vapor

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