How to populate an XML tree from the file system (LINQ to XML)

A common and useful application of XML trees is as a hierarchical name-value data store. You can populate an XML tree with hierarchical data, and then query it, transform it, and if necessary, serialize it. For this use, many of the XML-specific semantics, such as namespaces and white space behavior, aren't important. Instead, you're using the XML tree as a small, in-memory, single-user hierarchical database.

Example: Populate an XML tree and then query it

The following example uses recursion to populate an XML tree with data about the files in the local file system. It then queries the tree, totalling all the file sizes.

class Program
{
    static XElement CreateFileSystemXmlTree(string source)
    {
        DirectoryInfo di = new DirectoryInfo(source);
        return new XElement("Dir",
            new XAttribute("Name", di.Name),
            from d in Directory.GetDirectories(source)
            select CreateFileSystemXmlTree(d),
            from fi in di.GetFiles()
            select new XElement("File",
                new XElement("Name", fi.Name),
                new XElement("Length", fi.Length)
            )
        );
    }

    static void Main(string[] args)
    {
        XElement fileSystemTree = CreateFileSystemXmlTree("C:/Tmp");
        Console.WriteLine(fileSystemTree);
        Console.WriteLine("------");
        long totalFileSize =
            (from f in fileSystemTree.Descendants("File")
             select (long)f.Element("Length")).Sum();
        Console.WriteLine("Total File Size:{0}", totalFileSize);
    }
}

Module Module1
    Function CreateFileSystemXmlTree(ByVal source As String) As XElement
        Dim di As DirectoryInfo = New DirectoryInfo(source)
        Return <Dir Name=<%= di.Name %>>
                   <%= From d In Directory.GetDirectories(source) _
                       Select CreateFileSystemXmlTree(d) %>
                   <%= From fi In di.GetFiles() _
                       Select <File>
                                  <Name><%= fi.Name %></Name>
                                  <Length><%= fi.Length %></Length>
                              </File> %>
               </Dir>
    End Function

    Sub Main()
        Dim fileSystemTree As XElement = CreateFileSystemXmlTree("C:/Tmp")
        Console.WriteLine(fileSystemTree)
        Console.WriteLine("------")
        Dim totalFileSize As Long = _
            ( _
                From f In fileSystemTree...<File> _
                Select CLng(f.<Length>(0)) _
            ).Sum()
        Console.WriteLine("Total File Size:{0}", totalFileSize)
    End Sub
End Module

The example produces output similar to the following:

<Dir Name="Tmp">
  <Dir Name="ConsoleApplication1">
    <Dir Name="bin">
      <Dir Name="Debug">
        <File>
          <Name>ConsoleApplication1.exe</Name>
          <Length>4608</Length>
        </File>
        <File>
          <Name>ConsoleApplication1.pdb</Name>
          <Length>11776</Length>
        </File>
        <File>
          <Name>ConsoleApplication1.vshost.exe</Name>
          <Length>9568</Length>
        </File>
        <File>
          <Name>ConsoleApplication1.vshost.exe.manifest</Name>
          <Length>473</Length>
        </File>
      </Dir>
    </Dir>
    <Dir Name="obj">
      <Dir Name="Debug">
        <Dir Name="TempPE" />
        <File>
          <Name>ConsoleApplication1.csproj.FileListAbsolute.txt</Name>
          <Length>322</Length>
        </File>
        <File>
          <Name>ConsoleApplication1.exe</Name>
          <Length>4608</Length>
        </File>
        <File>
          <Name>ConsoleApplication1.pdb</Name>
          <Length>11776</Length>
        </File>
      </Dir>
    </Dir>
    <Dir Name="Properties">
      <File>
        <Name>AssemblyInfo.cs</Name>
        <Length>1454</Length>
      </File>
    </Dir>
    <File>
      <Name>ConsoleApplication1.csproj</Name>
      <Length>2546</Length>
    </File>
    <File>
      <Name>ConsoleApplication1.sln</Name>
      <Length>937</Length>
    </File>
    <File>
      <Name>ConsoleApplication1.suo</Name>
      <Length>10752</Length>
    </File>
    <File>
      <Name>Program.cs</Name>
      <Length>269</Length>
    </File>
  </Dir>
</Dir>
------
Total File Size:59089