我正在尝试在F#中使用SqlClient,使用SqlDataReader.ReadAsync
时遇到了困难。我正在尝试实现以下F#等效代码:
while (await reader.ReadAsync) { ... }
请问在F#中最佳的做法是什么?以下是我的完整程序。它可以工作,但我想知道是否有更好的方法。
open System
open System.Data.SqlClient
open System.Threading.Tasks
let connectionString = "Server=.;Integrated Security=SSPI"
module Async =
let AwaitVoidTask : (Task -> Async<unit>) =
Async.AwaitIAsyncResult >> Async.Ignore
// QUESTION: Is this idiomatic F#? Is there a more generally-used way of doing this?
let rec While (predicateFn : unit -> Async<bool>) (action : unit -> unit) : Async<unit> =
async {
let! b = predicateFn()
match b with
| true -> action(); do! While predicateFn action
| false -> ()
}
[<EntryPoint>]
let main argv =
let work = async {
// Open connection
use conn = new SqlConnection(connectionString)
do! conn.OpenAsync() |> Async.AwaitVoidTask
// Execute command
use cmd = conn.CreateCommand()
cmd.CommandText <- "select name from sys.databases"
let! reader = cmd.ExecuteReaderAsync() |> Async.AwaitTask
// Consume reader
// I want a convenient 'while' loop like this...
//while reader.ReadAsync() |> Async.AwaitTask do // Error: This expression was expected to have type bool but here has type Async<bool>
// reader.GetValue 0 |> string |> printfn "%s"
// Instead I used the 'Async.While' method that I defined above.
let ConsumeReader = Async.While (fun () -> reader.ReadAsync() |> Async.AwaitTask)
do! ConsumeReader (fun () -> reader.GetValue 0 |> string |> printfn "%s")
}
work |> Async.RunSynchronously
0 // return an integer exit code