蒸汽:使用参数在路由器 POST 调用中调用 REST API

Question

所以我正在尝试在我的一个 Vapor 端点中调用第二个端点。我有一个端点只是一个获取并且效果很好：

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)
})
}

这将正确返回连接响应 json。当我尝试做同样的事情时，但在需要一些参数的 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)
})
})
}

它失败了，flatMap说Cannot convert return expression of type 'EventLoopFuture<ConnectionResponse>' to return type 'ConnectionResponse'.

如您所见，除了 POST 参数的初始解码外，purchaseGET 调用与status相同。我做错了什么？

Answer 1

只需替换

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

跟

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

完整的工作代码可能如下所示

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有什么区别呢？

如果Future<Something>下一个结果，则使用flatMap，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用于非未来结果，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<>？它只是一个承诺，就像一个带有回调的对象。