Question

因此，我试图在我的Vapor端点之一中调用第二个端点。我有一个端点，只是一个不错的选择，而且运作良好：

router.get("status") { req -> Future<ConnectionResponse> in
  let client = try req.make(Client.self)
  let response = client.get("https://url.com/endpoint/")

  return response.flatMap(to: ConnectionResponse.self, { response in
    return try response.content.decode(ConnectionResponse.self)
  })
}

这将正确返回ConnectionResponse json。当我尝试执行相同的操作时，但是在需要一些参数的POST中，我无法弄清楚为什么编译器不允许我运行：

router.post("purchase") { req -> Future<ConnectionResponse> in
  return try req.content.decode(PurchaseRequest.self).map(to: ConnectionResponse.self, { response in
    let client = try req.make(Client.self)
    let response = client.get("https://url.com/endpoint/")

    return response.flatMap(to: ConnectionResponse.self, { response in
      return try response.content.decode(ConnectionResponse.self)
    })
  })
}

flatMap说Cannot convert return expression of type 'EventLoopFuture<ConnectionResponse>' to return type 'ConnectionResponse'失败。

如您所见，除了对POST参数进行初始解码之外，purchase GET调用与status相同。我究竟做错了什么？

Answer 1

只需替换

return try req.content.decode(PurchaseRequest.self).map(to: ConnectionResponse.self, { response in

使用

return try req.content.decode(PurchaseRequest.self).flatMap(to: ConnectionResponse.self, { response in

完整的工作代码可能看起来像这样

router.post("purchase") { req -> Future<ConnectionResponse> in
  return try req.content.decode(PurchaseRequest.self).flatMap { response in
    let client = try req.make(Client.self)
    let response = client.get("https://url.com/endpoint/")

    return response.flatMap { response in
      return try response.content.decode(ConnectionResponse.self)
    }
  }
}

那么map和flatMap有什么区别？

如果下一个结果为flatMap，则使用

Future<Something>，例如：

someDatabaseCall(on: container).flatMap { databaseResult1 in
    /// it will return Future<DatabaseResult>
    /// that's why we use `flatMap` above instead of `map`
    return anotherDatabaseCall(on: container) 
}

map用于非预期结果，例如：

someDatabaseCall(on: container).map { databaseResult1 in
    /// it will return non-future result
    /// that's we use `map` above instead of `flatMap`
    return "hello world" // just simple string
}

什么是Future<>？只是一个承诺，就像带有回调的对象一样。

蒸气：使用参数在路由器POST调用中调用REST API

1 个答案: