如何获取类型 F# 中字段的 ID

Question

How do I create a function to search on a database and return just the ID of a type?

Actually, I have a database, where I can search for a pair. The pair is a Type, in F#:

module Types = 

    [<CLIMutable>]
    type Pair = {
        Id :int64
        PairName : string
    }

My objective is to create a function, that return just the value of the ID (int) given a PairName. I Already have a function that returns a Pair, given this name.

      module Query = 

        let GetSingleByName name = querySingleAsync<Types.Bird> {
            script "SELECT * FROM Pair WHERE PairName = @Name LIMIT 1"
            parameters (dict ["Name", box name])
        }

How can I return just the integer? Not all the Type.Pair?

Answer 1

let getIdByName name = querySingleAsync<int64> {
    script "SELECT Id FROM Pair WHERE PairName = @Name LIMIT 1"
    parameters (dict ["Name", box name])
}

if this does not work, you'd have to provide the definition of querySingleAsync .

Alternatively:

let getIdByName name = async {
    let! single = getSingleByName name
    return single |> Option.map (fun pair -> pair.Id)
}

Answer 2

One of solutions that I find out was:

let GetSingleByName name = querySingleAsync<Types.Pair> {
                script "SELECT * FROM Pair WHERE PairName = @Name LIMIT 1"
                parameters (dict ["Name", box name])
            }



let GetIdByName (name:string)  = match GetSingleByName name |> Async.RunSynchronously  with
    | Some(pair)->  pair.Id
    | None -> 0 |> int64