在vb.net中解析xml

Question

I am given an XML file. It is formed like this:

      <?xml version="1.0" encoding="utf-8"?>
<dataset  xmlns="http://developer.cognos.com/schemas/xmldata/1/"      xmlns:xs="http://www.w3.org/2001/XMLSchema-instance">
    <!--
<dataset
    xmlns="http://developer.cognos.com/schemas/xmldata/1/"
    xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
        xs:schemaLocation="http://developer.cognos.com/schemas/xmldata/1/ xmldata.xsd">
-->
<metadata>
    <item name="Level" type="xs:short" precision="1"/>
    <item name="ID" type="xs:string" length="14"/>
    <item name="Name" type="xs:string" length="52"/>
</metadata>

<data>
    <row>
        <value>2</value>
        <value>101   </value>
        <value>Location 1</value>
    </row>
    <row>
        <value>2</value>
        <value>103   </value>
        <value>Location 2</value>
    </row>
</data>

I am having trouble parsing this. There are hundreds of articles online - but all of them have a different format than the data handed to me. Can anyone point me in the right direction for VB.NET on Framework 3.5? I am used to seeing data more like this:

    <item name="Future" collected="yes">

EDIT: So, I have tried this:

Dim reader As XmlTextReader = New XmlTextReader(fileToSave)

Do While (reader.Read())

Select Case reader.NodeType
                    Case XmlNodeType.Element 'Display beginning of element.
                        Console.Write("<" + reader.Name)
                        Console.WriteLine(">")
                    Case XmlNodeType.Text 'Display the text in each element.
                        Console.WriteLine(reader.Value)
                    Case XmlNodeType.EndElement 'Display end of element.
                        Console.Write("</" + reader.Name)
                        Console.WriteLine(">")
                End Select
            Loop

What I need is the Row items to be able to populate a combobox - this just gives me the same thing as the XML file:

    <dataset>
<metadata>
<item>
<item>
<item>
</metadata>
<data>
<row>
<value>
2
</value>
<value>
101   
</value>
<value>
Location 1
</value>
</row>
<row>
<value>
2
</value>
<value>
103   
</value>
<value>
Location 2
</value>
</row>
</data>
</dataset>

Answer 1

I believe the answer below should be to your liking. Most of my comments/editorials should explain the whole process. Turns out you're not the only person on stackoverflow having cognos dataset woes, lol. The example below was tested in LinqPad and returned desirable results.

Imports System.Data.Common
Imports System.Runtime.Serialization
Imports System.Xml.Xsl
Public Class Test

    'Note: If you don't put the <?xml...?> doctype the XML literals VB.NET gives you will not create an XDocument, but an XElement

    ' This the sample XML document from your question
    Private _xml As XDocument = <?xml version="1.0" encoding="utf-8"?>
    <dataset  xmlns="http://developer.cognos.com/schemas/xmldata/1/"      xmlns:xs="http://www.w3.org/2001/XMLSchema-instance">
    <!--
        <dataset
            xmlns="http://developer.cognos.com/schemas/xmldata/1/"
            xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
            xs:schemaLocation="http://developer.cognos.com/schemas/xmldata/1/ xmldata.xsd">
    -->
    <metadata>
        <item name="Level" type="xs:short" precision="1"/>
        <item name="ID" type="xs:string" length="14"/>
        <item name="Name" type="xs:string" length="52"/>
    </metadata>
    <data>
        <row>
            <value>2</value>
            <value>101   </value>
            <value>Location 1</value>
        </row>
        <row>
            <value>2</value>
            <value>103   </value>
            <value>Location 2</value>
        </row>
    </data>
    </dataset>

    ' This is a transform I found http://stackoverflow.com/questions/9465674/converting-a-cognos-xml-schema-file-to-xml-using-javascript-code, you're not the only one having trouble with this
    Private _xmlTransform As XDocument = <?xml version="1.0" encoding="utf-8"?>
    <xsl:stylesheet version="1.0" xmlns="http://tempuri.org/" xmlns:cog="http://developer.cognos.com/schemas/xmldata/1/" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
        <xsl:output method="xml" indent="yes" />

        <xsl:template match="//comment()" />

        <xsl:template match="/">
            <xsl:apply-templates />
        </xsl:template>

        <xsl:template match="cog:dataset">
            <rows>
                <xsl:apply-templates />
            </rows>
        </xsl:template>

        <xsl:template match="cog:metadata">
            <xsl:apply-templates />
        </xsl:template>

        <xsl:template match="cog:item">
            <xsl:apply-templates />
        </xsl:template>

        <xsl:template match="@name | @type | @length | @precision" />

        <xsl:template match="cog:data">
            <xsl:apply-templates />
        </xsl:template>

        <xsl:template match="cog:row">
            <row>
                <xsl:apply-templates />
            </row>
        </xsl:template>

        <xsl:template match="cog:value">
            <xsl:variable name="currentposition" select="count(./preceding-sibling::cog:value)+1" />
            <xsl:variable name="currentname" select="//cog:metadata/cog:item[$currentposition]/@name" />
            <xsl:element name="{$currentname}">
                <xsl:apply-templates />
            </xsl:element>
        </xsl:template>

        <xsl:template match="@* | node()">
            <xsl:copy>
                <xsl:apply-templates select="@* | node()"/>
            </xsl:copy>
        </xsl:template>
    </xsl:stylesheet>

    ' This is the XSLT .NET object that will allow us to translate your dataset into something usable
    private _tranform As XslCompiledTransform = new XslCompiledTransform()

    ' Meat & Potatoes, where the dataset will be set to
    public Property MainDataSet As DataSet

    Sub Main
        ' using XDocument, we can create a reader and then prepare the tranform...
        _tranform.Load(_xmlTransform.CreateReader(), new XsltSettings(true,true), Nothing)

        ' I am using "Using" here because, but you're more than welcome to use .Dispose, I'm a C# dev at heart, I'm just forced to code VB.NET for my day job
        Using _ds = new DataSet()   
            ' The XmlTextWrite constructor allows a StringBuilder; which will keep everything in-memory, per your comments
            Dim _sb As StringBuilder = new StringBuilder()

            ' Create an XmlTextWriter with the StringBuilder as the output-buffer
            Using _xmlWriter = XmlTextWriter.Create(_sb)                    
                ' Commit tranformation of the original dataset xml
                _tranform.Transform(_xml.CreateReader(), _xmlWriter)

                ' Have the interim DataSet read-in the new xml 
                _ds.ReadXml(new StringReader(_sb.ToString()), XmlReadMode.Auto)

                ' ... keeping it clean here... lol
                _xmlWriter.Close()

                ' Set the class property to the rendered dataset. 
                MainDataSet = _ds
            End Using       
        End Using

    End Sub
End Class

Answer 2

To extract data from XML in VB.Net, you could simply use VB.Net's XML literals (if you don't want to bother with XML transformation ).

Given your xml:

Dim xml As XDocument =  
                <?xml version="1.0" encoding="utf-8"?>
                <dataset  xmlns="http://developer.cognos.com/schemas/xmldata/1/"      xmlns:xs="http://www.w3.org/2001/XMLSchema-instance">
                    <metadata>
                        <item name="Level" type="xs:short" precision="1"/>
                        <item name="ID" type="xs:string" length="14"/>
                        <item name="Name" type="xs:string" length="52"/>
                    </metadata>
                    <data>
                        <row>
                            <value>2</value>
                            <value>101   </value>
                            <value>Location 1</value>
                        </row>
                        <row>
                            <value>2</value>
                            <value>103   </value>
                            <value>Location 2</value>
                        </row>
                    </data>
                </dataset>

you can import its namespace with

Imports <xmlns="http://developer.cognos.com/schemas/xmldata/1/">

and then simply query your data like in the following examples:

For Each element In xml...<value>
    Console.WriteLine(element.Value)
Next

Console.WriteLine("----------")

For Each element In xml...<row>
    For Each v in element.<value>
        Console.WriteLine(v.Value)
    Next
Next

Console.WriteLine("----------")

For Each element In xml...<row>
    Dim s = element.<value>.Select(Function(e) e.Value.Trim())
    Console.WriteLine(String.Join(" - ", s))
Next    

Output:

2
101   
Location 1
2
103   
Location 2
----------
2
101   
Location 1
2
103   
Location 2
----------
2 - 101 - Location 1
2 - 103 - Location 2

Answer 3

您可以使用System.IO.File.WriteAllLines或System.IO.File.WriteAllText方法，并将扩展名设置为XML