在System.Xml.XPath中启用XPath2查询(XPathException:无效令牌)
Microsofts System.Xml.XPath nuget-package,可用于.NET 4.6,声称支持XPath 1.0和2.0。 De documentation说descibes命名空间:在System.Xml.XPath中启用XPath2查询(XPathException:无效令牌)
System.Xml.XPath命名空间包含定义用于浏览和编辑XML信息项的游标模型的类作为XQuery 1.0和XPath 2.0数据模型的实例。
升级Visual Studio后,升级和我的所有项目到框架版本4.6我仍然无法获得最简单的XPath-2.0 for-expression工作。根据specification,他们应该工作。
我无法想象微软声称支持它实际上不支持的东西,所以显然我做错了什么。 如何正确使用XPath2查询?
[TestMethod]
public void TestXPath2()
{
// The System.Xml.XPath namespace contains the classes that define a cursor model for navigating and editing XML information items as instances of the
// XQuery 1.0 and XPath 2.0 Data Model.
var expression = "for $x in /Root/Foo/Bar return $x";
var compiledExpression = System.Xml.XPath.XPathExpression.Compile(expression);
// throws XPathException: "for ... has an invalid token"
}
P.S. 其实我是想什么,是为了得到这样的工作:
[TestMethod]
public void TestLibraryForCustomer1()
{
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 $curr in . return /Library/Writer[@ID=$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"]);
}
[TestMethod]
public void TestLibraryForCustomer2()
{
string xmlFromMessage = @"<Library>
<Writer ID=""writer1"">
<Name>Shakespeare</Name>
<Book><Title>Sonnet 18</Title></Book>
</Writer>
<Writer ID=""writer2"">
<Name>Tolkien</Name>
<Book><Title>The Hobbit</Title></Book>
<Book><Title>Lord of the Rings</Title></Book>
</Writer>
</Library>";
var titleXPathFromConfigurationFile = "./Title";
var writerXPathFromConfigurationFile = "../Name";
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);
}
}
我怀疑的XPath 2.0查询语言真正支持。
但是对于像您的要求那样简单的事情,XPath 1.0单行就足够了。
string xml = @"<Root>
<Foo ID=""foo1"">One</Foo>
<Foo ID=""foo2"">Two</Foo>
<Bar><FooRef REFID=""foo2"" /></Bar>
</Root>";
var doc = XDocument.Parse(xml);
var matchingFoo = doc.XPathSelectElement("/Root/Foo[@ID = //Bar/FooRef/@REFID]");
Assert.AreEqual("Two", matchingFoo.value);
对于超出XPath 1.0功能的查询,请尝试使用LINQ。
在您的扩展示例中,您想要将我们链接到书籍的作者。这是很容易在LINQ做加盟,这样的:
var 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 libraryDoc = XDocument.Parse(xmlFromMessage);
var library = from title in libraryDoc.Descendants("Title")
join writer in libraryDoc.Descendants("Writer")
on title.Parent.Element("WriterRef").Attribute("REFID").Value equals writer.Attribute("ID").Value
select new KeyValuePair<string, string>(title.Value, writer.Value);
现在library
是IEnumerable<KeyValuePair<string,string>>
与标题/写器配对。
也许你应该让你的例子更清楚,然后呢?你可能没有描述你想用什么实现来实现一个无法解释的目标,而是描述了你想要实现的目标,并将实现留给辩论(也就是XY问题)。 .NET中不支持XPath 2.0。使用LINQ,或在XPath 1.0中使用另一种方法。 '/ Root/Foo [@ID = // Bar/FooRef/@REFID]'选择*全部*'
对此评论+1。 “.Net中不支持XPath 2.0。”这是我一起工作的答案。我会尝试一些第三方库。 (仍然是:NuGet包描述提供它的作用:提供定义光标模型的类,用于导航和编辑可扩展标记语言(XML)信息项作为XQuery 1.0和XPath 2.0数据模型的实例 – realbart
数据模型和查询语言是独立的东西,但是在代码中我看不到任何迹象表明内置工具不能用来做你想做的事情,而且我甚至可以建议一种方法来做到这一点,如果我只是知道你想要做什么 – Tomalak
Tomalek指出正确:
- 的XPath 2.0未在.NET支持(在System.Xml.XPath),周期
- 的数据模型和查询语言是分开的东西。
所以我解决了它通过使用第三方XPath 2库,XPath2 nuget package。这允许表达式如
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。这确实不工作:
# does not work due to the absolute path
for $c in . return /Library/Writer[@ID=$c/WriterRef/@REFID]/Name
以供将来参考:安装的NuGet pacage后,此代码的工作:
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
using Wmhelp.XPath2;
namespace My.Library
{
[TestClass]
public 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"]);
}
[TestMethod]
public void TestLibraryForCustomer2()
{
string xmlFromMessage = @"<Library>
<Writer ID=""writer1"">
<Name>Shakespeare</Name>
<Book><Title>Sonnet 18</Title></Book>
</Writer>
<Writer ID=""writer2"">
<Name>Tolkien</Name>
<Book><Title>The Hobbit</Title></Book>
<Book><Title>Lord of the Rings</Title></Book>
</Writer>
</Library>";
var titleXPathFromConfigurationFile = "./Title";
var writerXPathFromConfigurationFile = "../Name";
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.XPath2SelectElement(titleXPath).Value;
var writer = book.XPath2SelectElement(writerXPath).Value;
yield return new KeyValuePair<string, string>(title, writer);
}
}
}
}
“中的XQuery 1.0和XPath 2.0数据模型”是有关标准的参考 - 这并不意味着xpath 2导航被支持。我无法立即在文档中找到它只解释了xpath 1的位置。0支持;如果我能的话,我会把它放在一个答案 – AakashM