XML search for string in a node and search for another string within that node as a result

Question

Hi 

I want to seach some XML for a string and then when i find that string I want to check the node that string is in for another string. See example below

<Objects  ObjectName="HelloObjectName"  ObjectAddress="2222">
      ...

</Objects>

How would I using C# search for string "2222" and then find out the ObjectName from within that node "HelloObjectName". 

Kind regards

Rob

Answer 1

You can use LINQ-to-XML:

XDocument doc = XDocument.Load(@"D:\Data.xml");    // The path of your XML document.
var objectName = (from n in doc.Descendants("Objects")
                        where n.Attribute("ObjectAddress").Value == "2222"
                        select n.Attribute("ObjectName")).FirstOrDefault();

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 2

Hi Marco

Excellent thanks I will give that a try

Kind regards

Rob

Answer 3

Hi Marco

You don't happen to know the correct namespace for xDocument do you because for some reason I am trying to add

Using System.Xml.Linq

but it cannot find System.Xml.Linq;

System.Xml on its own or System.Linq on its own but not System.Xml.Linq;

I am using .Net 4

Kind regards

Rob

Answer 4

Sorry I am being stupid I just need to add System.Xml.Linq into my references then I could used it.

Cheers

Rob

Answer 5

No problem :-)

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 6

Hi Marco

Thanks for your help on this, I have been away for a bit and only just come back to this.

I keep getting an error in my code 'Object reference not set to an instance of an object'. I know that the value it is trying to find for the ObjectAddress is in there but it still comes back with that error. Any ideas?

Kind regards

Rob

Answer 7

Perharps you need to check if the ObjectAddress attribute exists:

where n.Attribute("ObjectAddress") != null && n.Attribute("ObjectAddress").Value == "2222"

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 8

Thanks Marco

Its still coming back with Null unfortunately and the value for ObjectAddress definitely exists. Do I have to force the Linq to XML to read from the top of the XML file for something daft like that?

Kind regards

Rob

Answer 9

Could you post the XML file that gives you the error?

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 10

Hi Marco

Unfortunately I don't think I can, any other suggestions?

Kind regards

Rob

Answer 11

Try posting the full error message that you obtain.

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 12

The full error message is

'Object reference not set to an instance of an object'

The object name is definitely coming back as 'Null'. But when I just search the XML file myself I find the value.

Kind regards

Rob

Answer 13

Without seeing the XML input file, it is difficult to understand the problem. With the example file I have created, everything works fine, so probably the error depends on the actual structure of your file.

Can you create a small XML file to reproduce the error, that you can send me?

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 14

Hi Marco

I think I might be onto something now, I have stripped everything out apart from one node and then I searched for that Nodes ObjectAddress attribute value knowing it was there and I got a result back for ObjectName attribute value, but when I added another 2 Object Nodes in and searched on one of those ObjectAddress attribute values I got the following error:

'There are multiple root elements. Line 10, position 3'

Kind regards

Rob

Answer 15

It seems that there is an error in your XML file definition, but if I don't see it, I can tell you what is the problem.

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 16

Actually I have solved that, that's my fault, because I stripped everything back and did not have a root node surrounding everything. I can get the values back now. I still have problem though because obviously something in my XML before I stripped it must have something in it that is causing a Null to be returned.

Kind regards

Rob

Answer 17

I'm sorry, but without an XML file that reproduces the error, I can't help you.

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva

Answer 18

No worries thanks for your help anyway.

Cheers

Rob

Answer 19

We found the solution, it is because of the namespace in the XML file, you need to place the namespace before your descendant node and it seems
to do the trick.
When I stripped the XML doc back and had no namespace, there was no problem, when I put it back in there was. So adding it before the
decendant node sorts out the problem.
Thanks for your help Marco.
Cheers
Rob
See below......
XNamespace ns = "http://namespace.org/NamespaceExample.xsd"                        
XDocument doc = XDocument.Load(@"D:\Data.xml");    // The path of your XML document.
var objectName = (from n in doc.Descendants(ns + "Objects")
			where n.Attribute("ObjectAddress") != null && n.Attribute("ObjectAddress").Value == "2222"
                        select n.Attribute("ObjectName")).FirstOrDefault();

Answer 20

OK, so it was a namespace problem... It makes sense.

---

Marco Minerva [MCPD]
Blog: http://blogs.ugidotnet.org/marcom
Twitter: @marcominerva