Q:

Linq to XML - Find an element

I am sure that this is basic and probably was asked before, but I am only starting using Linq to XML.
I have a simple XML that i need to read and write to.
<Documents>
...
    <Document>
      <GUID>09a1f55f-c248-44cd-9460-c0aab7c017c9-0</GUID>
      <ArchiveTime>2012-05-15T14:27:58.5270023+02:00</ArchiveTime>
      <ArchiveTimeUtc>2012-05-15T12:27:58.5270023Z</ArchiveTimeUtc>
      <IndexDatas>
        <IndexData>
          <Name>Name1</Name>
          <Value>Some value</Value>
          <DataType>1</DataType>
          <CreationTime>2012-05-15T14:27:39.6427753+02:00</CreationTime>
          <CreationTimeUtc>2012-05-15T12:27:39.6427753Z</CreationTimeUtc>
        </IndexData>
        <IndexData>
          <Name>Name2</Name>
          <Value>Some value</Value>
          <DataType>3</DataType>
          <CreationTime>2012-05-15T14:27:39.6427753+02:00</CreationTime>
          <CreationTimeUtc>2012-05-15T12:27:39.6427753Z</CreationTimeUtc>
        </IndexData>
   ...
 </IndexDatas>
</Document>
...
</Documents>

I have a "Documents" node that contains bunch of "Document" nodes.
I have GUID of the document and a "IndexData" name. 
I need to find the document by GUID and check if it has "IndexData" with some name.
If it does not have it i need to add it.
Any help would be apreciated, as i have problem with reading and searching trough elements.
Currently I am trying to use (in C#):
IEnumerable<XElement> xmlDocuments = from c in XElement
                                        .Load(filePath)
                                        .Elements("Documents") 
                                         select c;

// fetch document
 XElement documentElementToEdit = (from c in xmlDocuments where 
                    (string)c.Element("GUID").Value == GUID select c).Single();

EDIT
xmlDocuments.Element("Documents").Elements("Document")

This returns no result, even tho xmlDocuments.Element("Documents") does. It looks like i cant get Document nodes from Documents node.

A:

You can find those docs (docs without related name in index data) with below code, after that you could add your elements to the end of IndexData elements.
var relatedDocs = doc.Elements("Document")
   .Where(x=>x.Element("GUID").Value == givenValue)
   .Where(x=>!x.Element("IndexDatas")
              .Elements("IndexData")
              .Any(x=>x.Element("Name") == someValue);

