[RESOLVED] Updating a shared XML file

Hi

I have XML file on a server that can be updated by many client workstations. So my code looks lie this:

VB Code:

Public sub UpdateControl()
    Dim Doc As New XmlDocument
    Dim fs As FileStream
 
    Try
      fs = New FileStream(_BatchListFile, FileMode.Open, FileAccess.ReadWrite, FileShare.None)
      ' Load the XML through the filestream
      Doc.Load(fs)
 
      ' Pick up node using SelectSingleNode and update
 
      fs.position = 0
     ' Write back the Xml file
      Doc.Save(fs)
    Catch ex as Exception
      throw new Exception("", ex)
    Finally
       if not(fs is nothing) Then
         fs.close
         fs = nothing
       End If
    End Try
End Sub

My problem is that sometimes I end up with the updated XML having a trailing part of text which seems to happen when I update the innerText of a node and the text becomes shorter. For example

Original Xml

VB Code:

<?xml version="1.0" encoding="utf-8">
<root>
<customer>
  <surname>Very Long Surname</surname>
</customer>
<customer>
' more customer data
</customer>
</root>

Updated Xml. surname innertext reduced following removal of Long

VB Code:

<?xml version="1.0" encoding="utf-8">
<root>
<customer>
  <surname>Very Surname</surname>
</customer>
<customer>
' more customer data
</customer>
</root></root> ' <<<<<< trailing text in updated file

SO my question is:

Am I using the right method to update the file. I know I could delete the file and recreate it but this seems a bit dirty to me.

Secondly, what is the best way to update an existing file.

Thanks

why open the XML doc from a filestream? the XmlDocument object can load directly from a file..

XML is nothing more than a text file in a specific format.... when you read in an XML document, using the xmldocument.load method.. it is read and closed immediatly... the xmldocument has all the info about the xml from the file, but it is now independant of the file.. you need to call the xmldocument.save method to save any changes to the XML back to the file.. but since like I said its a text file.. it simply rewrites the xml file each time you save...

kleinma

The main reason to open the XML file through the filestream is to keep it locked while I'm updating it. Of course in my actual application I have a mechanism to retry when the file is locked by another client. Is there anyway I can lock the file so that while its loaded in the XmlDomDocument object someone else doesn't load it.

no there isn't because the XMLDoc is not connected to the actual XML file in any way.. it just reads the file or writes a file... the manipulation of the XML data in the XMLDocument is only being manipulated in the object itself.. not in the file... changes are never made until the save method is called...

I am not sure why you are getting a weird cutoff in your XML document.. I would probably need to see the code that does the actual XML manipulation between the load and the save in order to try to figure out whats going on

kleinma

Thanks for responding. As you can see thats why I'm using a stream to keep the file locked. I'll try a few things such as setting the length of the Filestream to 0 using the SetLength method before the save and see if it works.

Found the solution. I use fs.SetLength(0) to set the stream to empty and then I save back the XML into it.

VB Code:

Public sub UpdateControl()
    Dim Doc As New XmlDocument
    Dim fs As FileStream
 
    Try
      fs = New FileStream(_BatchListFile, FileMode.Open, FileAccess.ReadWrite, FileShare.None)
      ' Load the XML through the filestream
      Doc.Load(fs)
 
      ' Pick up node using SelectSingleNode and update
 
      fs.SetLength(0)   ' This clears any previous data from the file
     ' Write back the Xml file
      Doc.Save(fs)
    Catch ex as Exception
      throw new Exception("", ex)
    Finally
       if not(fs is nothing) Then
         fs.close
         fs = nothing
       End If
    End Try
End Sub