如何將由XmlProvider自動提供的選擇類型<...> .DomainTypes轉換爲F＃中的枚舉？

Question

比方說，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> 

並希望將其轉變成F＃地圖：

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正確地推斷出XML屬性mapping的類型是XmlProvider<...>.DomainTypes.MappingChoice。但是，我找不到將此類型轉換爲mappingType的方法。

首先，我試圖XML屬性mapping轉換成在隨後將它希望字符串枚舉mappingType，但即使這被證明是對我來說太困難了......

在上面的代碼重寫類型helpMe：

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

然後代???到

string e.Strength 

給我"Some(1-1)"或"Some(1-n)"爲helpMe.mapping這不是我想要的。
如果我試圖取代???到

string (defaultArg e.Mapping "") 

然後FSI理所當然地抱怨：

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

Answer 1

好了，從字符串轉換爲mappingType，您可以定義一個小助手功能：

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

這將使您能夠編寫如下投影：

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

現在，這裏有點作弊，因爲它只是叫e.Mapping.Value。如果e.Mapping是None，這可能會引發異常，但由於e.Mapping始終有一個值，因此可以使用此處提供的數據。