SelectSingleNode() function returns null

Question

I am developing a program for reading RDL files (Reporting Services Report Files). Assume my XML is the following:

 

<?xml version="1.0" encoding="utf-8"?> <Report xmlns="http://schemas.microsoft.com/sqlserver/reporting/2005/01/reportdefinition" xmlns:rd="http://schemas.microsoft.com/SQLServer/reporting/reportdesigner">   <DataSources>     <DataSource Name="DataSource">       <ConnectionProperties>         <IntegratedSecurity>true</IntegratedSecurity>         <ConnectString></ConnectString>         <DataProvider></DataProvider>       </ConnectionProperties>       <rdataSourceID>136c762c-789b-4fa7-b4a8-b60c584c387b</rdataSourceID>     </DataSource>   </DataSources>   <BottomMargin>2.5cm</BottomMargin>   <RightMargin>2.5cm</RightMargin>   <rdrawGrid>true</rdrawGrid>   <InteractiveWidth>8.5in</InteractiveWidth>   <rd:GridSpacing>0.25cm</rd:GridSpacing>   <rdnapToGrid>true</rdnapToGrid> . . . </Report>

 

When I write the following code to get the "DataSources" Node, the SelectSingleNode() function returns null:

 

doc.SelectSingleNode("DataSources")

or

doc.DocumentElement.SelectSingleNode("DataSources")

or

doc.SelectSingleNode("//DataSources")

or

doc.DocumentElement.SelectSingleNode("//DataSources")

or

doc.SelectSingleNode("/DataSources")

or

doc.DocumentElement.SelectSingleNode("/DataSources")

 

 

why?

Answer 1

There is a default namespace declaration you need to take into account by using an XmlNamespaceManager as follows:

Code Snippet

Dim doc As New XmlDocument()

doc.Load("file.xml")

Dim mgr As New XmlNamespaceManager(doc.NameTable)

mgr.AddNamespace("df", "http://schemas.microsoft.com/sqlserver/reporting/2005/01/reportdefinition")

Dim node As XmlNode = doc.SelectSingleNode("/df:Report/df:DataSources", mgr)

 

 

Answer 2

I am still having the problem with this method returning null.  I've recreated Martin's example. 
My XML is below:

Code Snippet

<?xml version="1.0" encoding="utf-8"?>

<ACORD xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.ACORD.org/standards/PC_Surety/ACORD1.4.1/xml/">

<SignonRq>

<ClientApp>

<Org>Online</Org>

</ClientApp>

</SignonRq>

<InsuranceSvcRq>

<RqUID>00000000-0000-0000-0000-001030582207</RqUID>

<PersAutoPolicyQuoteInqRq>

<RqUID>00000000-0000-0000-0000-001030582207</RqUID>

<PersPolicy>

<ContractTerm>

<EffectiveDt>2008-07-08</EffectiveDt>

</ContractTerm>

</PersPolicy>

</PersAutoPolicyQuoteInqRq>

</InsuranceSvcRq>

</ACORD>

 

And my code, which throws an exception every time:

Code Snippet

static void Main(string[] args)

{

XmlDocument doc = new XmlDocument();

doc.Load("my.xml");

XmlNamespaceManager xnm = new XmlNamespaceManager(doc.NameTable);

xnm.AddNamespace("ACORD", "http://www.ACORD.org/standards/PC_Surety/ACORD1.4.1/xml/");

XmlNode node = doc.DocumentElement.SelectSingleNode("/ACORD:InsuranceSvcRq", xnm);

if (node == null)

throw new NullReferenceException();

}

 

Answer 3

That element is down in the document so you either need to give the full path or you need to use // in your XPath e.g.

Code Snippet

//ACORD:InsuranceSvcRq

 

 

The full path looks like

Code Snippet

/ACORD:ACORD/ACORD:InsuranceSvcRq

 

 

As a third alternative, as you call SelectSingleNode on the DocumentElement (my sample calls it on the document node), you could use

ACORD:InsuranceSvcRq

without a leading slash.

Answer 4

Outstanding - that works great!  I found this notation to be the most helpful:

Code Snippet

//ACORD:InsuranceSvcRq

 

Because it simply searches for that element, you don't have to specify the full path.  Thanks for your help.

Answer 5

But note that using // is expensive as it searches through the whole document. It does not matter for small documents but if you have large documents you might want to avoid using // in your XPath expressions if you can write a more precise XPath expression.