如何在F＃中使用这个EF Core C＃异步方法？

Question

我正在使用带有实体框架的F＃，我无法理解使用F＃的C＃异步方法。 尽管其他与类似问题相关的SO答案无法真正解决。

这是我尝试使用下面的代码，最初是同步的：

let getAirport (id: Guid) =
    use context = new MyContext()
    context.Flights.Find id
    |> (fun x -> if box x = null then None else Some x)

和它的async对应物：

let getAirportAsync (id: Guid) =
    async {
        use context = new MyContext()
        let! flight = context.Airports.FindAsync id |> Async.AwaitTask
        return (fun x -> if box x = null then None else Some x)
    }

但是，当两者都被称为主要：

[<EntryPoint>]
let main argv =
    let myGuid = Guid.NewGuid()
    let airport = {
        Id = myGuid
        Name = "Michelle"
        X = 42.0
        Y = 42.0
    }
    AirportRepository.addAirport airport
    let thisAirport = AirportRepository.getAirport myGuid
    let thisAirportToo = AirportRepository.getAirportAsync myGuid |> Async.RunSynchronously
    assert (thisAirport = Some airport)
    assert (thisAirportToo = Some airport)
    0

它无法编译：

  Program.fs(61, 13): [FS0001] The type '('a -> 'a option)' does not support the 'equality' constraint because it is a function type
  Program.fs(61, 30): [FS0001] This expression was expected to have type    ''a -> 'a option'    but here has type    ''b option'

我读：

• https://medium.com/jettech/f-async-guide-eb3c8a2d180a
• https://docs.microsoft.com/en-us/dotnet/fsharp/tutorials/asynchronous-and-concurrent-programming/async
• C＃async / await方法到F＃？

我认为使用async C＃方法的过程是：

• 将C＃方法传递给|> Async.AwaitTask
• 传递结果let!
• 返回结果
• 将所有内容包装在async块中，该块构成async F＃函数的主体
• 通过将新async创建的F＃函数传递给|> Async.RunSynchronously

我在这里错过了什么？

Answer 1

问题是在getAirportAsync您丢弃flight并返回该功能。 修复很简单：

let getAirportAsync (id: Guid) =
    async {
        use context = new MyContext()
        let! flight = context.Airports.FindAsync id |> Async.AwaitTask
        return if box flight = null then None else Some flight
    }