Use namespaces with XPath in VB.NET with XML

Question

I'm trying to select a specific <Relationships> node with XML in VB.NET. The problem which occurs is that, with my set XPath, I get the error:

Namespace Manager or XsltContext needed. This query has a prefix, variable, or user-defined function.

This is the XPath I use:

Dim parentNode As XmlNode = myXmlDocument.SelectSingleNode("/pkg:package/pkg:part[@pkg:name='/_rels/.rels']/pkg:xmlData/Relationships[@xmlns='http://schemas.openxmlformats.org/package/2006/relationships']")

I understand that you're then supposed to add a namespace manager, which I tried doing. However, I get mixed up with all the definitions and examples I have seen and therefore I haven't got the code to work:

Dim namespaceManager As XmlNamespaceManager = New XmlNamespaceManager(myXmlDocument.NameTable)
namespaceManager.AddNamespace("xmlns:pkg", "http://schemas.microsoft.com/office/2006/xmlPackage")
namespaceManager.AddNamespace("xmlns", "http://schemas.openxmlformats.org/package/2006/relationships")

The code above resulted in the following error at the second namespace I'm adding:

Prefix "xmlns" is reserved for use by XML.

My XML file looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<?mso-application progid="PowerPoint.Show"?>
<pkg:package
    xmlns:pkg="http://schemas.microsoft.com/office/2006/xmlPackage">
    <pkg:part pkg:name="/_rels/.rels" pkg:contentType="application/vnd.openxmlformats-package.relationships+xml" pkg:padding="512">
        <pkg:xmlData>
            <Relationships
                xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
                <Relationship Id="rId3" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/extended-properties" Target="docProps/app.xml"/>
                <Relationship Id="rId2" Type="http://schemas.openxmlformats.org/package/2006/relationships/metadata/core-properties" Target="docProps/core.xml"/>
                <Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="ppt/presentation.xml"/>
            </Relationships>
        </pkg:xmlData>
    </pkg:part>
</pkg:package>

I'm not getting how you're supposed to work with these namespaces in VB.NET and incorperate them into your XPath. Is there anyone who now how to solve this and select the <Relationships> node?

Yitzhak Khabinsky · Accepted Answer · 2019-09-22 18:16:00Z

1

It is much better to use LINQ to XML API while dealing with XML. It is available for more than a decade.

VB.NET

Dim myXmlDocument As XDocument = XDocument.Load("e:\temp\package.xml")

Dim ns0 As XNamespace = "http://schemas.microsoft.com/office/2006/xmlPackage"
Dim ns1 As XNamespace = "http://schemas.openxmlformats.org/package/2006/relationships"


Dim Relationships As XElement = myXmlDocument.Descendants(ns1 + "Relationships").FirstOrDefault()

Console.WriteLine(Relationships)

answered Sep 22, 2019 at 18:16

Yitzhak Khabinsky

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DanielBoven Over a year ago

I hadn't thought about using LINQ to XML, I haven't used that before. Now that I have looked into it, it works way better and leaves a cleaner code as well. Thanks a lot for your answer, I will mark it as the correct answer ^

Yitzhak Khabinsky · Accepted Answer · 2019-09-22 16:58:30Z

0

You need to add a namespace prefix like follows.

VB.NET

Dim namespaceManager As XmlNamespaceManager = New XmlNamespaceManager(myXmlDocument.NameTable)
namespaceManager.AddNamespace("xmlns:pkg", "http://schemas.microsoft.com/office/2006/xmlPackage")
namespaceManager.AddNamespace("xmlns:ns1", "http://schemas.openxmlformats.org/package/2006/relationships")

After that, the following XPath expression will give access to the Relationships fragment.

/pkg:package/pkg:part/pkg:xmlData/ns1:Relationships

answered Sep 22, 2019 at 16:58

Yitzhak Khabinsky

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1 Comment

DanielBoven Over a year ago

Thank you for the answer. I have tried it, but now I'm getting System.Xml.XPath.XPathException: 'The prefix of namespace ns1 is not defined.' as an error. How can I solve that?

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