问题描述
我有一些带有默认命名空间的 xml
I have some xml with default namespace
<a xmlns='urn:test.Schema'><b/><b/></a>
并想统计
我必须如何定义
XmlNamespaceManager nsmgr = ????
Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);
使断言变为真?
到目前为止我已经尝试过(使用 nunit):
I have tried so far (using nunit):
[Test]
[Ignore("Why does this not work?")]
public void __DoesNotWork_TestSelectWithDefaultNamespace()
{
// xml to parse with defaultnamespace
string xml = @"<a xmlns='urn:test.Schema'><b/><b/></a>";
XmlDocument doc = new XmlDocument();
doc.LoadXml(xml);
// fails because xpath does not have the namespace
//!!!!
Assert.AreEqual(2, doc.SelectNodes("//b").Count);
// using XPath defaultnamespace
XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
nsmgr.AddNamespace("", "urn:test.Schema");
// This will fail with dotnet 3.5sp1. Why?
//!!!!
Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);
}
[Test]
public void TestSelectWithoutNamespaces_Ok()
{
// xml to parse without namespace
string xml = @"<a><b/><b/></a>";
XmlDocument doc = new XmlDocument();
doc.LoadXml(xml);
// works ok
Assert.AreEqual(2, doc.SelectNodes("//b").Count);
// works ok
XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);
}
[Test]
public void TestSelectWithNamespacesPrefixed_Ok()
{
// xml to parse with defaultnamespace
string xml = @"<a xmlns='urn:test.Schema'><b/><b/></a>";
XmlDocument doc = new XmlDocument();
doc.LoadXml(xml);
// using XPath namespace via alias "t". works ok but xpath is to complicated
XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
nsmgr.AddNamespace("t", doc.DocumentElement.NamespaceURI);
Assert.AreEqual(2, doc.SelectNodes("//t:b", nsmgr).Count);
}
推荐答案
// This will fail with dotnet 3.5sp1. Why?
//!!!!
Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);
这是一个常见问题.在 XPath 中,任何不带前缀的名称都被假定为无命名空间".为了选择属于命名空间的元素,在任何 XPath 表达式中,它们的名称都必须以与该命名空间相关联的前缀为前缀.AddNamespace()
方法正是为了这个目的.它在特定命名空间和特定前缀之间创建绑定.然后,如果在 XPath 表达式中使用此前缀,则可以选择以它为前缀的元素.
This is a FAQ. In XPath any unprefixed name is assumed to be in "no namespace". In order to select elements that belong to a namespace, in any XPath expression their names must be prefixed with a prefix that is associated with this namespace. The AddNamespace()
method serves exactly this purpose. It creates a binding between a specific namespace and a specific prefix. Then, if this prefix is used in an XPath expression, the element prefixed by it can be selected.
它写在 XPath W3C 规范: "节点测试中的 QName 使用表达式上下文中的命名空间声明扩展为扩展名称.这与对开始和结束标记中的元素类型名称进行扩展的方式相同,除了使用 xmlns 声明的默认命名空间未使用:如果 QName 没有前缀,则命名空间 URI 为空".
It is written in the XPath W3C spec: "A QName in the node test is expanded into an expanded-name using the namespace declarations from the expression context. This is the same way expansion is done for element type names in start and end-tags except that the default namespace declared with xmlns is not used: if the QName does not have a prefix, then the namespace URI is null".
参见:w3.org/TR/xpath/#node-tests .
See this at: w3.org/TR/xpath/#node-tests .
因此,任何不带前缀的名称都被视为无命名空间".在提供的 XML 文档中,无命名空间"中没有 b
元素,这就是 XPath 表达式 //b
根本不选择任何节点的原因.
So, any unprefixed name is considered to be in "no namespace". In the provided XML document there are no b
elements in "no namespace" and this is why the XPath expression //b
selects no nodes at all.
使用:
XmlNamespaceManager nsmanager = new XmlNamespaceManager(doc.NameTable);
nsmanager.AddNamespace("x", "urn:test.Schema");
及以后:
Assert.AreEqual(2, doc.SelectNodes("//x:b", nsmanager).Count);
记住:注册命名空间的全部目的是能够在任何 XPath 表达式中使用前缀(在本例中为 x
).
Remember: The whole purpose of registering the namespace is to be able to use the prefix (in this case x
) in any XPath expression.
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