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how to append a xml file in c# if exists, or make new if not?

Posted on 2010-11-22
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Last Modified: 2012-05-10
i am adding tracing for audit purposes of a simple process i have built as an .exe and set in the scheduler to run every 10 minutes. i want to have the application output the results into an xml file.

if the file exists then open and append data to it, if it does not exist i want to create a new xml file that will be persisted and used on next run.

here is my code now, what do i need to add, how do i open the xml file (on c:/file.xml) and use it to append nodes to?

also i think my code is like a newbs, so some help in showing me the correct streamlined way would help me learn best practice with C#/ XML

string err = "";
        XmlDocument doc = new XmlDocument();// Create the XML Declaration, and append it to XML document

        XmlDeclaration dec = doc.CreateXmlDeclaration("1.0", null, null);
        doc.AppendChild(dec);// Create the root element

        XmlElement root = doc.CreateElement("STATS");
        doc.AppendChild(root);

        // Create URL's            
        XmlElement urlNode = doc.CreateElement("keepalive");
        urlNode.SetAttribute("runTime", DateTime.Now.ToString());

        try
        {
            WebProxy wp = new WebProxy("http://proxy.ml.com:8083/");
            WebClient w = new WebClient();
            w.Proxy = wp;

            if (w.DownloadString("http://wwww.idealcoding.com") != "")
                urlNode.SetAttribute("result", "UP");
            else
                urlNode.SetAttribute("result", "DOWN");
        }
        catch (Exception ex)
        {
            err = ex.Message;
            urlNode.SetAttribute("result", "DOWN");
        }
        finally {
            root.AppendChild(urlNode);
            doc.Save("c:/keepAlive.xml");
        }

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this is my XML file:
 
<STATS>
  <keepalive runTime="11/22/2010 9:40:43 AM" result="UP" /> 
 </STATS>

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Question by:realcoding
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7 Comments
 
LVL 52

Expert Comment

by:Carl Tawn
ID: 34188933
What is it you want to add to the file, a new <STATS /> everytime it runs or a new <keepalive /> adding to STATS?
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Author Comment

by:realcoding
ID: 34189033
i want to just add keepalive nodes, such that each run of the app will log the time it ran and result.
if the file exists i want to load it into the xml object and add a keepalive node with the current runs info and so on... if the xml file does not exist then do as i do here and create a new one.

but as it stands every run of the app creates and over-writes the xml file leaving only one node , not very useful.
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LVL 18

Assisted Solution

by:Richard Lee
Richard Lee earned 800 total points
ID: 34189081
Okay the approach I would take here, and its a slightly different thinking from you is that I would have a Xml Serializable Audit object. I would then read the contents of the file and deserialize into and instance of the Audit class and then add the new entries to this object and overwrite the existing file.

Xml Serializer and Deserializer class:
http://avantprime.com/articles/view-article/13/xml-serialization-and-de-serialization-helper-class-using-generics

Use the StreamReader and StreamWriter classes to manipulate the file on disk.
http://www.c-sharpcorner.com/UploadFile/puranindia/StreamReaderStreamWriterClasses11242009235459PM/StreamReaderStreamWriterClasses.aspx

DaTribe
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LVL 52

Accepted Solution

by:
Carl Tawn earned 1200 total points
ID: 34189085
OK, try replacing these four lines:
        XmlDeclaration dec = doc.CreateXmlDeclaration("1.0", null, null);
        doc.AppendChild(dec);// Create the root element

        XmlElement root = doc.CreateElement("STATS");
        doc.AppendChild(root);

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With:
    XmlElement root;

   if (File.Exists(@"c:\keepAlive.xml"))
   {
         doc.Load(@"c:\keepAlive.xml");
         root = doc.SelectSingleNode("/STATS");
   }
   else
   {
        XmlDeclaration dec = doc.CreateXmlDeclaration("1.0", null, null);
        doc.AppendChild(dec);// Create the root element

        root = doc.CreateElement("STATS");
        doc.AppendChild(root);
   }

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You may also want to move the filename into a variable to save you typing it over and over again.
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LVL 18

Expert Comment

by:Richard Lee
ID: 34189103
Also to handle when this file gets very large I would write to a new write each hour / day. You could create folders for further organization. File would be suffixed with Date & Time. Folders would be suffixed with Date.

DaTribe
0
 

Author Closing Comment

by:realcoding
ID: 34189826
why would you use a serializable object? whats the gain?
0
 
LVL 18

Expert Comment

by:Richard Lee
ID: 34189903
The gain for me would be simply manipulating this object easily with c# and then in the end simply turning it back to XML. Avoid the hassles with XML plus another huge bonus would be I could add or remove properties from the Audit class and deserialization would still be successful and as the file contents are over-written when saving then there would be no problem saving the new structure.

I save myself development time and hassles. More maintainable solution. In this instance as its every 10 minutes mission critical performance is not required - still some of the suggestions I provided work around that.

DaTribe
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