選択型を DTO に変換する

選択型は特殊なレコード型で表現する

使用されている選択肢を示す「タグ」

各可能なケースに関連するデータを含む「フィールド」

e.g.

code:domain.fs

type Name =

{ First: String50

Last: String50 }

type Example =

| A

| B of int

| C of string list

| D of Name

code:dto.fs

type NameDto =

{ First: string

Last: string }

type ExampleDto =

{ Tag: string

BData: Nullable<int>

CData: string[]

DData: NameDto }

シリアライズパイプラインの実装

code:dto.fs

let nameDtoFromDomain (name: Domain.Name): NameDto =

let first = name.First |> String50.value

let last = name.Last |> String50.value

{ First = first; Last = last }

let fromDomain (domainObj: Domain.Example): ExampleDto =

let nullBData = Nullable()

let nullCData = null

let nullDData = Unchecked.defaultof<NameDto>

match domainObj with

| A ->

{ Tag = "A"; BData = nullBData; CData = nullCData; DData = nullDData }

| B i ->

let bdata = Nullable i

{ Tag = "B"; BData = bdata; CData = nullCData; DData = nullDData }

| C strList ->

let cdata = strList |> List.toArray

{ Tag = "C"; BData = nullBData; CData = cdata; DData = nullDData }

| D name ->

let ddata = name |> nameDtoFromDomain

{ Tag = "D"; BData = nullBData; CData = nullCData; DData = ddata }

デシリアライズパイプラインの実装

「タグ」フィールドでマッチさせ、それぞれのケースを処理する

code:dto.fs

let nameDtoToDomain (nameDto: NameDto): Result<Domain.Name,string> =

result {

let! first = nameDto.First |> String50.create

let! last = nameDto.Last |> String50.create

return { First = first; Last = last }

}

let toDomain dto: Result<Domain.Example,string> =

match dto.Tag with

| "A" -> Ok A

| "B" ->

if dto.BData.HasValue then

dto.BData.Value |> B |> Ok

else

Error "B data not expected to be null"

| "C" ->

match dto.CData with

| null -> Error "C data not expected to be null"

| _ -> dto.CData |> Array.toList |> C |> Ok

| "D" ->

match box dto.DData with

| null -> Error "D data not expected to be null"

| _ ->

dto.DData

|> nameDtoToDomain // Result<Domain.Name,string>

|> Result.map D // Result<Example.D,string>

| _ ->

let msg = sprintf "Tag '%s' not recognized" dto.Tag

Error msg