Read XML and add element if missing

[catlook]

My xml layout has changed since going into production. So, i need to read the file and, if the Facility element is missing, add it in.

 

Old xml:

<SrvConfig>

<HostAddress>dev123.home.com</HostAddress>

<WhsNumber>03</WhsNumber>

<SrvPath>/appl/03/wt4090/</SrvPath>

</SrvConfig>

 

Desired xml:

<SrvConfig>

<HostAddress>dev123.home.com</HostAddress>

<WhsNumber>03</WhsNumber>

<SrvPath>/appl/03/wt4090/</SrvPath>

<Facility>MFG</Facility>

</SrvConfig>

 

So my code to read it:

 

            XmlNode node;
           XmlDocument doc = new XmlDocument();

           //open xml file
           doc.Load(srvCfgPathAndName);

           //find element of interest
           node = doc.SelectSingleNode("/SrvConfig/HostAddress");
           _currServerIP = node.InnerText;
           node = doc.SelectSingleNode("/SrvConfig/WhsNumber");
           _currWhs = node.InnerText;
           node = doc.SelectSingleNode("/SrvConfig/SrvPath");
           _currPath = node.InnerText;

           //since Facility wasn't part of original design we 
           //may need to add it for existing devices
           node = doc.SelectSingleNode("/SrvConfig/Facility");
           if (node == null)
           {
                 //somehow insert it and write it back out  
           }

 

Can someone helpme out with the insert and write bit? Thanks!

[alreadyused]

simple answer is this:

• create a new fragment in the target document; i think it's XmlDocumentFragment in vb, but that should get you pointed in the right direction

• set the INNER XML of your fragment ("<Facility>someval</Facility"> or "<Facility />")

• then you need the parent node you want to add it to (in this case SrvConfig)

• 
  and tell the parent node to append the fragment.
  

 

Here's a longer answer though; you're bound to run into this problem over and over and over and well you get the idea.

 

So ideally you would create a class to handle this, but you could get by with just two functions. The basic logic is like this, you create a get and a set that do the following (lazy pseudo-code)

 

getInfo(parentNode: XmlNode, elementName: String): String
 targetNode=parentNode.selectSingleNode(elementName)

 if targetNode is nothing
   return String.Empty
 else
   return targetNode.innerText
 end if

end getInfo


setInfo(parentNode: XmlNode, elementName: String, value: String): Void
 targetNode=parentNode.selectSingleNode(elementName)
 
 if targetNode is nothing
   // use solution from my short answer above to create the targetnode, ending it with: 
   targetNode = parentNode.addChild(xFrag)
 end if

 // now you have a targetNode so...
 targetNode.innerText = value

end setInfo

 

 

now what you have is:

 

a get function getInfo that returns String.Empty when it doesn't find the element (or if the element's inner text is nothing)

 

a set function that will create the node if DNE and then set the value you want.

[catlook]

Great notes!!

 

so i now have filled in the missing snippet with :

 

            node = doc.SelectSingleNode("/SrvConfig/Facility");
           if (node == null)
           {
               XmlDocumentFragment myFrag = doc.CreateDocumentFragment();
               myFrag.InnerXml = "<Facility>MFG</Facility>";
               XmlNode parentNode;
               parentNode = doc.SelectSingleNode("/SrvConfig");
               parentNode.AppendChild(myFrag);
           }

 

It compiles and runs without error, however the xml file doesn't contain the added node. So, I must need a write or something. I found XmlDocument Write and WriteTo functions but wasn't sure if either applied.

 

So, how do I save my painstakingly added element?

[catlook]

I meant to say I found WriteContentTo and Write functions.

 

I was looking at WriteContentTo, and maybe that's the right direction. ONly, does this mean I have to reopen the document as a FileStream, use that to instantiate a XmlTextWriter and then rewrite each element? Or how does it know to just add the one at the end?

 

Ok, I'll sit quiet and wait now. Thanks for your assstance!

[alreadyused]

if you put a breakpoint and inspect the xdoc in memory, you'll see that it's there.

 

however, that's only in memory so you need to save your changes using:

doc.save(path)

after you have appended the frag