我正在编写使用XPath查询解析XML文件的类。 XML可能看起来像这样：
<?xml version="1.0" encoding="UTF-8"?>
<Doc>
<Name id="aa">Alice</Name>
<Name id="bb">Bob</Name>
<Name id="cc">Candice</Name>
<Person nameid="aa"></Person>
<Person nameid="bb"></Person>
<Person nameid="aa"></Person>
</Doc>
所需的输出是：
Alice
Bob
Alice
我使用C＃来解析这些人：
// these are dynanically defined elsewhere.
const string personXPath = "/Doc/Person";
const string nameXPath = "/Doc/Name[@id=current()/@nameid]"; // <== modify this line
void ParseXDocument(XDocument doc)
{
foreach (var personElement in doc.XPathSelectElements(personXPath))
{
var nameElement = personElement.XPathSelectElement(nameXPath);
Console.WriteLine(nameElement.Value);
}
}
这可以通过修改nameXPath变量来实现吗？ （我的软件不应该知道＆＃34; XML结构，将XML映射到我自己的类的唯一方法是x路径，它们是可配置的。）
另一个例子：
[TestMethod]
public void TestLibrary()
{
string xmlFromMessage = @"<Library>
<Writer ID=""writer1""><Name>Shakespeare</Name></Writer>
<Writer ID=""writer2""><Name>Tolkien</Name></Writer>
<Book><WriterRef REFID=""writer1"" /><Title>Sonnet 18</Title></Book>
<Book><WriterRef REFID=""writer2"" /><Title>The Hobbit</Title></Book>
<Book><WriterRef REFID=""writer2"" /><Title>Lord of the Rings</Title></Book>
</Library>";
var titleXPathFromConfigurationFile = "./Title";
var writerXPathFromConfigurationFile = "??? what to put here ???";
var library = ExtractBooks(xmlFromMessage, titleXPathFromConfigurationFile, writerXPathFromConfigurationFile).ToDictionary(b => b.Key, b => b.Value);
Assert.AreEqual("Shakespeare", library["Sonnet 18"]);
Assert.AreEqual("Tolkien", library["The Hobbit"]);
Assert.AreEqual("Tolkien", library["Lord of the Rings"]);
}
public IEnumerable<KeyValuePair<string,string>> ExtractBooks(string xml, string titleXPath, string writerXPath)
{
var library = XDocument.Parse(xml);
foreach(var book in library.Descendants().Where(d => d.Name == "Book"))
{
var title = book.XPathSelectElement(titleXPath).Value;
var writer = book.XPathSelectElement(writerXPath).Value;
yield return new KeyValuePair<string, string>(title, writer);
}
}
答案 0 :(得分：0)
您应该将从第一个XPath获得的值放到第二个表达式中。
const string personXPath = "/Doc/Person";
const string nameXPath = "/Doc/Name[@id='{0}']";
foreach (var personElement in doc.XPathSelectElements(personXPath))
{
var nameid = personElement.Attribute("nameid").Value;
var nameElement = doc.XPathSelectElement(string.Format(nameXPath, nameid));
Console.WriteLine(nameElement.Value);
}
答案 1 :(得分：0)
Sombody正确指出：
所以我通过使用第三方XPath 2库XPath2 nuget package来解决它。这允许像
这样的表达式for $c in . return ../Writer[@ID=$c/WriterRef/@REFID]/Name
请注意，我需要使用从书到作家的相对路径。这样做不工作：
# does not work due to the absolute path
for $c in . return /Library/Writer[@ID=$c/WriterRef/@REFID]/Name
供将来参考：此代码在安装nuget pacage之后有效：
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
using Wmhelp.XPath2;
namespace My.Library
{
[TestClass]
class WmhelpTests
{
[TestMethod]
public void LibraryTest()
{
string xmlFromMessage = @"<Library>
<Writer ID=""writer1""><Name>Shakespeare</Name></Writer>
<Writer ID=""writer2""><Name>Tolkien</Name></Writer>
<Book><WriterRef REFID=""writer1"" /><Title>King Lear</Title></Book>
<Book><WriterRef REFID=""writer2"" /><Title>The Hobbit</Title></Book>
<Book><WriterRef REFID=""writer2"" /><Title>Lord of the Rings</Title></Book>
</Library>";
var titleXPathFromConfigurationFile = "./Title";
var writerXPathFromConfigurationFile = "for $curr in . return ../Writer[@ID=$curr/WriterRef/@REFID]/Name";
var library = ExtractBooks(xmlFromMessage, titleXPathFromConfigurationFile, writerXPathFromConfigurationFile).ToDictionary(b => b.Key, b => b.Value);
Assert.AreEqual("Shakespeare", library["King Lear"]);
Assert.AreEqual("Tolkien", library["The Hobbit"]);
Assert.AreEqual("Tolkien", library["Lord of the Rings"]);
}
public IEnumerable<KeyValuePair<string, string>> ExtractBooks(string xml, string titleXPath, string writerXPath)
{
var library = XDocument.Parse(xml);
foreach (var book in library.Descendants().Where(d => d.Name == "Book"))
{
var title = book.XPath2SelectElement(titleXPath).Value;
var writer = book.XPath2SelectElement(writerXPath).Value;
yield return new KeyValuePair<string, string>(title, writer);
}
}
}
}
我使用了一个脏修复：在我的xpath中，我将“current（）”替换为实际值。这样，当前函数的行为类似于the xslt-standard。
class MyClass
{
// these are dynanically defined elsewhere.
const string personXPath = "/Doc/Person";
const string nameXPath = "/Doc/Name[@id=current()/@nameid]";
XElement _node;
void ParseXDocument(XDocument doc)
{
foreach (var personElement in doc.XPathSelectElements(personXPath))
{
_node = personElement; // my actual code is a bit cleaner
var nameElement = personElement.XPathSelectElement(PreParse(nameXPath));
Console.WriteLine(nameElement.Value);
}
}
/// <summary>
/// Pre-evaluates calls to current()
/// </summary>
/// <param name="xpath"></param>
/// <returns></returns>
private string PreParse(string xpath)
{
var sb = new StringBuilder();
foreach (var part in Tokenize(xpath))
{
if (part.Trim().StartsWith("current()"))
{
var query = part.Replace("current()", ".");
sb.Append("'")
.Append(EvaluateXPath(query))
.Append("'");
}
else
{
sb.Append(part);
}
}
return sb.ToString();
}
private IEnumerable<string> Tokenize(string path)
{
var begin = 0;
for (var i = 0; i < path.Length; i++)
{
if ("[=]".Contains(path[i]))
{
yield return path.Substring(begin, i - begin);
yield return path[i].ToString();
begin = i + 1;
}
}
yield return path.Substring(begin);
}
private string EvaluateXPath(string xpath)
{
var result = _node.XPathEvaluate(xpath);
if (result is IEnumerable)
foreach (var node in (IEnumerable)result)
return (node as XElement)?.Value ?? (node as XAttribute).Value;
return string.Format(CultureInfo.InvariantCulture, "{0}", result);
}
}