在 F# 中检索记录字段的值时获取可选类型的值

Question

我有一个定义如下的类型：

type Employee = {
    Id:    Guid
    Name:  string
    Phone: string
    Email: Option<string>
}

和这种类型的实例：

let emp = {
    Id = Guid "bc07e94c-b376-45a2-928b-508b888802c9"
    Name = "A"
    Phone = "B"
    Email = Some "E"
}

我想使用反射从该记录类型中提取字段名称和值，如下所示：

let getFieldValueMappingOfARecordType (data: 'T) : seq<string * obj> =
    let fieldValueMapping =
        data.GetType()
        |> FSharpType.GetRecordFields
        |> Seq.map (
            fun propertyInfo ->

                    (propertyInfo.Name, data |> propertyInfo.GetValue)
        )
    fieldValueMapping

然后用employee类型的实例调用上面的函数

let mapping = getFieldValueMappingOfARecordType emp
            |> Seq.toList

给我们：

val mapping : (string * obj) list =
  [("Id", bc07e94c-b376-45a2-928b-508b888802c9); ("Name", "A"); ("Phone", "B");
   ("Email", Some "E")]

到目前为止，它在非可选类型上运行良好。但在可选类型的情况下，它会将字段的值返回为 Some value 或 None。我想做的是在字段有 Some value 时获取 value 或在字段为 None 时获取 null。

基本上如下：

val mapping : (string * obj) list =
  [("Id", bc07e94c-b376-45a2-928b-508b888802c9); ("Name", "A"); ("Phone", "B");
   ("Email", "E")]

或者如果员工实例如下所示：

let emp = {
    Id = Guid "bc07e94c-b376-45a2-928b-508b888802c9"
    Name = "A"
    Phone = "B"
    Email = None
}

然后，

val mapping : (string * obj) list =
  [("Id", bc07e94c-b376-45a2-928b-508b888802c9); ("Name", "A"); ("Phone", "B");
   ("Email", null)]

这是我目前所拥有的（非工作代码）：

open System
open Microsoft.FSharp.Reflection
open System.Reflection

type Employee = {
    Id:    Guid
    Name:  string
    Phone: string
    Email: Option<string>
}

let emp = {
    Id = Guid "bc07e94c-b376-45a2-928b-508b888802c9"
    Name = "A"
    Phone = "B"
    Email = Some "E"
}

let getSomeOrNull (t: Type) (o: obj) =
    let opt = typedefof<option<_>>.MakeGenericType [| t |]
    match (o :?> opt) with
    | Some s ->
        s
    | None ->
        null

let getValues (data: 'T) =
    let values =
        data.GetType()
        |> FSharpType.GetRecordFields
        |> Array.map (
            fun propertyInfo ->
                let value =
                    data |> propertyInfo.GetValue

                let isOption =
                    propertyInfo.PropertyType.IsGenericType && propertyInfo.PropertyType.GetGenericTypeDefinition() = typedefof<Option<_>>

                match isOption with
                | true ->
                    (propertyInfo.Name, (getSomeOrNull propertyInfo.PropertyType value))
                | false ->
                    (propertyInfo.Name, value)
        )
    values

getValues emp
|> printfn "%A"

Answer 1

我认为唯一的方法就是反思：

let getSomeOrNull (t: Type) (o: obj) =
    if isNull o then null
    else t.GetProperty("Value").GetValue(o)

Answer 2

我认为这应该可以解决问题：

let getSomeOrNull (o: obj) =
    match o with
    | :? Option<string> as o -> a |> Option.toObj > box
    | _ -> null

在 F# 中检索记录字段的值时获取可选类型的值

Get value of optional types when retrieving value of record fields in F#

reflection

f#

record