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A veces, resulta útil enumerar todos los nodos de un árbol, por ejemplo, para saber exactamente cómo afecta un método o una propiedad al árbol. En el ejemplo siguiente para C# y Visual Basic se enumeran los nodos de un árbol. Cada nodo se representa mediante una expresión XPath que especifica la ubicación del nodo en el árbol.
Nota
No resulta particularmente útil ejecutar expresiones XPath con LINQ to XML. Las consultas LINQ to XML funcionan mejor que las expresiones XPath y son mucho más eficaces. No obstante, como forma de identificar nodos en el árbol XML, XPath funciona bien.
Ejemplo: Uso de XPath para enumerar todos los nodos de un árbol
En este ejemplo se muestra una función con el nombre GetXPath que genera una expresión XPath específica para cualquier nodo del árbol XML. Realiza esta acción incluso cuando los nodos están en un espacio de nombres. Los elementos de las expresiones XPath generadas tienen prefijos de espacios de nombres según sea necesario.
Primero, el ejemplo crea un pequeño árbol XML que contiene varios tipos de nodos. Después recorre en iteración los nodos e imprime la expresión XPath para cada nodo.
La declaración XML no es un nodo del árbol.
Este es el árbol XML que actúa como entrada:
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<?target data?>
<Root AttName="An Attribute" xmlns:aw="http://www.adventure-works.com">
<!--This is a comment-->
<Child>Text</Child>
<Child>Other Text</Child>
<ChildWithMixedContent>text<b>BoldText</b>otherText</ChildWithMixedContent>
<aw:ElementInNamespace>
<aw:ChildInNamespace />
</aw:ElementInNamespace>
</Root>
Esta es la lista de nodos del árbol XML, definida por las expresiones XPath:
/processing-instruction()
/Root
/Root/@AttName
/Root/@xmlns:aw
/Root/comment()
/Root/Child[1]
/Root/Child[1]/text()
/Root/Child[2]
/Root/Child[2]/text()
/Root/ChildWithMixedContent
/Root/ChildWithMixedContent/text()[1]
/Root/ChildWithMixedContent/b
/Root/ChildWithMixedContent/b/text()
/Root/ChildWithMixedContent/text()[2]
/Root/aw:ElementInNamespace
/Root/aw:ElementInNamespace/aw:ChildInNamespace
Este es el código del ejemplo:
public static class MyExtensions
{
private static string GetQName(XElement xe)
{
string prefix = xe.GetPrefixOfNamespace(xe.Name.Namespace);
if (xe.Name.Namespace == XNamespace.None || prefix == null)
return xe.Name.LocalName.ToString();
else
return prefix + ":" + xe.Name.LocalName.ToString();
}
private static string GetQName(XAttribute xa)
{
string prefix =
xa.Parent.GetPrefixOfNamespace(xa.Name.Namespace);
if (xa.Name.Namespace == XNamespace.None || prefix == null)
return xa.Name.ToString();
else
return prefix + ":" + xa.Name.LocalName;
}
private static string NameWithPredicate(XElement el)
{
if (el.Parent != null && el.Parent.Elements(el.Name).Count() != 1)
return GetQName(el) + "[" +
(el.ElementsBeforeSelf(el.Name).Count() + 1) + "]";
else
return GetQName(el);
}
public static string StrCat<T>(this IEnumerable<T> source,
string separator)
{
return source.Aggregate(new StringBuilder(),
(sb, i) => sb
.Append(i.ToString())
.Append(separator),
s => s.ToString());
}
public static string GetXPath(this XObject xobj)
{
if (xobj.Parent == null)
{
XDocument doc = xobj as XDocument;
if (doc != null)
return ".";
XElement el = xobj as XElement;
if (el != null)
return "/" + NameWithPredicate(el);
// The XPath data model doesn't include white space text nodes
// that are children of a document, so this method returns null.
XText xt = xobj as XText;
if (xt != null)
return null;
XComment com = xobj as XComment;
if (com != null)
return
"/" +
(
com
.Document
.Nodes()
.OfType<XComment>()
.Count() != 1 ?
"comment()[" +
(com
.NodesBeforeSelf()
.OfType<XComment>()
.Count() + 1) +
"]" :
"comment()"
);
XProcessingInstruction pi = xobj as XProcessingInstruction;
if (pi != null)
return
"/" +
(
pi.Document.Nodes()
.OfType<XProcessingInstruction>()
.Count() != 1 ?
"processing-instruction()[" +
(pi
.NodesBeforeSelf()
.OfType<XProcessingInstruction>()
.Count() + 1) +
"]" :
"processing-instruction()"
);
return null;
}
else
{
XElement el = xobj as XElement;
if (el != null)
{
return
"/" +
el
.Ancestors()
.InDocumentOrder()
.Select(e => NameWithPredicate(e))
.StrCat("/") +
NameWithPredicate(el);
}
XAttribute at = xobj as XAttribute;
if (at != null)
return
"/" +
at
.Parent
.AncestorsAndSelf()
.InDocumentOrder()
.Select(e => NameWithPredicate(e))
.StrCat("/") +
"@" + GetQName(at);
XComment com = xobj as XComment;
if (com != null)
return
"/" +
com
.Parent
.AncestorsAndSelf()
.InDocumentOrder()
.Select(e => NameWithPredicate(e))
.StrCat("/") +
(
com
.Parent
.Nodes()
.OfType<XComment>()
.Count() != 1 ?
"comment()[" +
(com
.NodesBeforeSelf()
.OfType<XComment>()
.Count() + 1) + "]" :
"comment()"
);
XCData cd = xobj as XCData;
if (cd != null)
return
"/" +
cd
.Parent
.AncestorsAndSelf()
.InDocumentOrder()
.Select(e => NameWithPredicate(e))
.StrCat("/") +
(
cd
.Parent
.Nodes()
.OfType<XText>()
.Count() != 1 ?
"text()[" +
(cd
.NodesBeforeSelf()
.OfType<XText>()
.Count() + 1) + "]" :
"text()"
);
XText tx = xobj as XText;
if (tx != null)
return
"/" +
tx
.Parent
.AncestorsAndSelf()
.InDocumentOrder()
.Select(e => NameWithPredicate(e))
.StrCat("/") +
(
tx
.Parent
.Nodes()
.OfType<XText>()
.Count() != 1 ?
"text()[" +
(tx
.NodesBeforeSelf()
.OfType<XText>()
.Count() + 1) + "]" :
"text()"
);
XProcessingInstruction pi = xobj as XProcessingInstruction;
if (pi != null)
return
"/" +
pi
.Parent
.AncestorsAndSelf()
.InDocumentOrder()
.Select(e => NameWithPredicate(e))
.StrCat("/") +
(
pi
.Parent
.Nodes()
.OfType<XProcessingInstruction>()
.Count() != 1 ?
"processing-instruction()[" +
(pi
.NodesBeforeSelf()
.OfType<XProcessingInstruction>()
.Count() + 1) + "]" :
"processing-instruction()"
);
return null;
}
}
}
class Program
{
static void Main(string[] args)
{
XNamespace aw = "http://www.adventure-works.com";
XDocument doc = new XDocument(
new XDeclaration("1.0", "utf-8", "yes"),
new XProcessingInstruction("target", "data"),
new XElement("Root",
new XAttribute("AttName", "An Attribute"),
new XAttribute(XNamespace.Xmlns + "aw", aw.ToString()),
new XComment("This is a comment"),
new XElement("Child",
new XText("Text")
),
new XElement("Child",
new XText("Other Text")
),
new XElement("ChildWithMixedContent",
new XText("text"),
new XElement("b", "BoldText"),
new XText("otherText")
),
new XElement(aw + "ElementInNamespace",
new XElement(aw + "ChildInNamespace")
)
)
);
doc.Save("Test.xml");
Console.WriteLine(File.ReadAllText("Test.xml"));
Console.WriteLine("------");
foreach (XObject obj in doc.DescendantNodes())
{
Console.WriteLine(obj.GetXPath());
XElement el = obj as XElement;
if (el != null)
foreach (XAttribute at in el.Attributes())
Console.WriteLine(at.GetXPath());
}
}
}
Module Module1
<System.Runtime.CompilerServices.Extension()> _
Private Function StrCat(Of T)(ByVal source As IEnumerable(Of T), _
ByVal separator As String) As String
Return _
source.Aggregate(New StringBuilder(), _
Function(sb, i) sb _
.Append(i.ToString()) _
.Append(separator), _
Function(s) s.ToString())
End Function
<System.Runtime.CompilerServices.Extension()> _
Public Function GetXPath(ByVal xobj As XObject) As String
Dim retStr As String
If xobj.Parent Is Nothing Then
Dim doc As XDocument = TryCast(xobj, XDocument)
If doc IsNot Nothing Then
Return "."
End If
Dim el As XElement = TryCast(xobj, XElement)
If el IsNot Nothing Then
Return ("/" & NameWithPredicate(el))
End If
' The XPath data model doesn't include white space text nodes
' that are children of a document, so this method returns null.
Dim xt As XText = TryCast(xobj, XText)
If xt IsNot Nothing Then
Return Nothing
End If
Dim com As XComment = TryCast(xobj, XComment)
If com IsNot Nothing Then
If com.Document().Nodes().OfType(Of XComment)().Count() <> 1 Then
Return "/comment()[" & (com.NodesBeforeSelf().OfType _
(Of XComment)().Count() + 1) & "]"
Else
Return "/comment()"
End If
End If
Dim pi As XProcessingInstruction = TryCast(xobj, XProcessingInstruction)
If pi IsNot Nothing Then
If pi.Document.Nodes().OfType(Of XProcessingInstruction)(). _
Count() <> 1 Then
Return "/processing-instruction()[" & _
(pi.NodesBeforeSelf().OfType(Of XProcessingInstruction)() _
.Count() + 1) & "]"
Else
Return "/processing-instruction()"
End If
End If
Else
Dim el As XElement = TryCast(xobj, XElement)
If el IsNot Nothing Then
Return "/" & el.Ancestors().InDocumentOrder(). _
Select(Function(e) NameWithPredicate(e)) _
.StrCat("/") & NameWithPredicate(el)
End If
Dim at As XAttribute = TryCast(xobj, XAttribute)
If at IsNot Nothing Then
Return "/" & at.Parent().AncestorsAndSelf().InDocumentOrder(). _
Select(Function(e) NameWithPredicate(e)).StrCat("/") & _
"@" & GetQName(at)
End If
Dim com As XComment = TryCast(xobj, XComment)
If com IsNot Nothing Then
retStr = "/" & com.Parent.AncestorsAndSelf().InDocumentOrder(). _
Select(Function(e) NameWithPredicate(e)).StrCat("/") & "comment()"
If com.Parent().Nodes().OfType(Of XComment)().Count() <> 1 Then
retStr &= "[" & (com.NodesBeforeSelf().OfType(Of XComment)().Count() + 1) & "]"
End If
Return retStr
End If
Dim cd As XCData = TryCast(xobj, XCData)
If cd IsNot Nothing Then
retStr = "/" & cd.Parent.AncestorsAndSelf().InDocumentOrder(). _
Select(Function(e) NameWithPredicate(e)).StrCat("/") & "text()"
If cd.Parent.Nodes().OfType(Of XText)().Count() <> 1 Then
retStr &= "[" & (cd.NodesBeforeSelf().OfType(Of XText)(). _
Count() + 1) & "]"
End If
Return retStr
End If
Dim tx As XText = TryCast(xobj, XText)
If tx IsNot Nothing Then
retStr = "/" & tx.Parent.AncestorsAndSelf().InDocumentOrder(). _
Select(Function(e) NameWithPredicate(e)).StrCat("/") & "text()"
If tx.Parent.Nodes().OfType(Of XText)().Count() <> 1 Then
retStr &= "[" & (tx.NodesBeforeSelf().OfType(Of XText)(). _
Count() + 1) & "]"
End If
Return retStr
End If
Dim pi As XProcessingInstruction = TryCast(xobj, XProcessingInstruction)
If pi IsNot Nothing Then
retStr = "/" & pi.Parent.AncestorsAndSelf().InDocumentOrder(). _
Select(Function(e) NameWithPredicate(e)). _
StrCat("/") & "processing-instruction()"
If pi.Parent.Nodes().OfType(Of XProcessingInstruction)().Count() <> 1 Then
retStr &= "[" & (pi.NodesBeforeSelf().OfType(Of XProcessingInstruction)(). _
Count() + 1) & "]"
End If
End If
End If
Return Nothing
End Function
Private Function GetQName(ByVal xe As XElement) As String
Dim prefix As String = xe.GetPrefixOfNamespace(xe.Name.Namespace)
If xe.Name.Namespace = XNamespace.None Or prefix Is Nothing Then
Return xe.Name.LocalName.ToString()
Else
Return prefix + ":" & xe.Name.LocalName.ToString()
End If
End Function
Private Function GetQName(ByVal xa As XAttribute) As String
Dim prefix As String = _
xa.Parent.GetPrefixOfNamespace(xa.Name.Namespace)
If xa.Name.Namespace = XNamespace.None Or prefix Is Nothing Then
Return xa.Name.ToString()
Else
Return prefix + ":" & xa.Name.LocalName
End If
End Function
Public Function NameWithPredicate(ByVal el As XElement) As String
If el.Parent IsNot Nothing AndAlso el.Parent.Elements(el.Name).Count() <> 1 Then
Return GetQName(el) + "[" & _
(el.ElementsBeforeSelf(el.Name).Count() + 1) & "]"
Else
Return GetQName(el)
End If
End Function
Sub Main()
Dim aw As XNamespace = "http://www.adventure-works.com"
Dim doc As XDocument = _
<?xml version='1.0' encoding="utf-8" standalone='yes'?>
<?target data?>
<Root AttName='An Attribute' xmlns:aw='http://www.adventure-works.com'>
<!--This is a comment-->
<Child>Text</Child>
<Child>Other Text</Child>
<ChildWithMixedContent>text<b>BoldText</b>otherText</ChildWithMixedContent>
<aw:ElementInNamespace>
<aw:ChildInNamespace/>
</aw:ElementInNamespace>
</Root>
doc.Save("Test.xml")
Console.WriteLine(File.ReadAllText("Test.xml"))
Console.WriteLine("------")
For Each obj As XObject In doc.DescendantNodes()
Console.WriteLine(obj.GetXPath())
Dim el As XElement = TryCast(obj, XElement)
If el IsNot Nothing Then
For Each at As XAttribute In el.Attributes()
Console.WriteLine(at.GetXPath())
Next
End If
Next
End Sub
End Module
Este ejemplo produce el siguiente resultado:
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<?target data?>
<Root AttName="An Attribute" xmlns:aw="http://www.adventure-works.com">
<!--This is a comment-->
<Child>Text</Child>
<Child>Other Text</Child>
<ChildWithMixedContent>text<b>BoldText</b>otherText</ChildWithMixedContent>
<aw:ElementInNamespace>
<aw:ChildInNamespace />
</aw:ElementInNamespace>
</Root>
------
/processing-instruction()
/Root
/Root/@AttName
/Root/@xmlns:aw
/Root/comment()
/Root/Child[1]
/Root/Child[1]/text()
/Root/Child[2]
/Root/Child[2]/text()
/Root/ChildWithMixedContent
/Root/ChildWithMixedContent/text()[1]
/Root/ChildWithMixedContent/b
/Root/ChildWithMixedContent/b/text()
/Root/ChildWithMixedContent/text()[2]
/Root/aw:ElementInNamespace
/Root/aw:ElementInNamespace/aw:ChildInNamespace
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