xml - 如何将 XmlProvider<...>.DomainTypes 自动提供的选择类型转换为 F# 中的枚举？

Question

假设我有以下 XML:

<?xml version="1.0" encoding="UTF-16"?>
<iAmConfused>
    <helpMe feeling="anger" strength="100" mapping="1-1" />
    <helpMe feeling="frustration" strength="15" mapping="1-n" />
    <helpMe feeling="helplessness" strength="365" mapping="1-1" />
    <helpMe feeling="despair" strength="-1" mapping="1-n" />
</iAmConfused>

并且想要将其转换为 F# map :

open System.Xml
open System.Xml.Linq
open FSharp.Data

type mappingType =
    | oneToOneMapping = 00
    | oneToManyMapping = 01

type helpMe = {
    strength : int;
    mapping : mappingType}

type iAmConfusedXmlType = XmlProvider<"""<?xml version="1.0" encoding="UTF-16"?><iAmConfused><helpMe feeling="anger" strength="100" mapping="1-1" /><helpMe feeling="frustration" strength="15" mapping="1-n" /><helpMe feeling="helplessness" strength="365" mapping="1-1" /><helpMe feeling="despair" strength="-1" mapping="1-n" /></iAmConfused>""">

let iAmConfusedXml = iAmConfusedXmlType.Parse("""<?xml version="1.0" encoding="UTF-16"?><iAmConfused><helpMe feeling="anger" strength="100" mapping="1-1" /><helpMe feeling="frustration" strength="15" mapping="1-n" /><helpMe feeling="helplessness" strength="365" mapping="1-1" /><helpMe feeling="despair" strength="-1" mapping="1-n" /></iAmConfused>""")

let iWantThisMap =
    iAmConfusedXml.GetHelpMes()
    |> Seq.map (fun e -> e.Feeling, {
        strength = e.Strength;
        mapping = ???})
    |> Map.ofSeq

XmlProvider正确推断 XML 属性的类型 mapping成为XmlProvider<...>.DomainTypes.MappingChoice 。但是，我找不到将此类型转换为 mappingType 的方法。

首先我尝试转换 XML 属性 mapping字符串，希望然后将其转换为枚举 mappingType ，但即使这对我来说也太难了......

重写上面代码中的helpMe类型:

type helpMe = {
    strength : int;
    mapping : string}

然后替换 ???至

string e.Strength

给我"Some(1-1)"或"Some(1-n)"对于 helpMe.mapping这不是我想要的。
如果我尝试替换 ???至

string (defaultArg e.Mapping "")

那么 FSI 理所当然地提示:

test.fs(165,38): error FS0001: This expression was expected to have type
    'a option    
but here has type
    XmlProvider<...>.DomainTypes.MappingChoice

Answer 1

好吧，要将字符串转换为 mappingType，您可以定义一个小辅助函数:

let convert m =
    match m with
    | "1-1" -> mappingType.oneToOneMapping
    | _ -> mappingType.oneToManyMapping

这将使您能够编写如下投影:

let iWantThisMap =
    iAmConfusedXml.GetHelpMes()
    |> Seq.map (fun e -> e.Feeling, {
        strength = e.Strength;
        mapping = (e.Mapping.Value |> convert) })
    |> Map.ofSeq

现在，这里有一点作弊，因为它只是调用e.Mapping.Value。如果 e.Mapping 为 None，这可能会引发异常，但根据此处提供的数据，它可以正常工作，因为 e.Mapping 始终有一个值.