Update an Existing Element Using Linq

[Edwin]

I am trying to write an application among which one of the functions is to
determine the number of unique extensions found in a directory and all of
its sub directories. I am trying to use Linq to XML to do this.

Below is the code being used to accomplish what I am trying to do. In the
"if" statement, I am trying to update the <Count></CountElement to
"TESTING". However what I will really want is to add 1 to the existing
numerical value.

Your help is greatly appreciated!


System.IO.FileI nfo myCurrentFile;
System.Xml.Linq .XElement myFileCountCurr entElement;

var Extensions = new XElement("Count ", (from Extension in
_myFileExtensio nCount.LinqXDoc ument.Descendan ts("Extension" ) where
Extension.Eleme nt("Name").Valu e == myCurrentFile.E xtension.ToLowe r()
select new
{
Name =
Extension.Eleme nt("Name").Valu e,
Count =
Extension.Eleme nt("Count").Val ue,
}));


// An unaccounted file extension has been found. Let's add it.
if (Extensions.IsE mpty == true)
{
myFileCountCurr entElement = _myFileExtensio nCount.LinqXDoc ument.Root;
myFileCountCurr entElement =
_myFileExtensio nCount.AppendXm lElement(myFile CountCurrentEle ment,
"Extension" , null);
_myFileExtensio nCount.AppendXm lElement(myFile CountCurrentEle ment,
"Name", myCurrentFile.E xtension.ToLowe r());
_myFileExtensio nCount.AppendXm lElement(myFile CountCurrentEle ment,
"Count", "1");
}
else
{
Extensions.SetV alue("TESTING") ;
}

Below is the XML output that I am getting.


<?xml version="1.0" encoding="utf-8" ?>
- <FileExtensions >
- <Extension>
<Name>.m4b</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.docx</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.doc</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.xls</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.xlsx</Name>
<Count>1</Count>
</Extension>
</FileExtensions>

[Martin Honnen]

Re: Update an Existing Element Using Linq

Edwin wrote:

Below is the XML output that I am getting.
>
>
<?xml version="1.0" encoding="utf-8" ?>
- <FileExtensions >
- <Extension>
<Name>.m4b</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.docx</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.doc</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.xls</Name>
<Count>1</Count>
</Extension>
- <Extension>
<Name>.xlsx</Name>
<Count>1</Count>
</Extension>
</FileExtensions>

Here is an example that adds 1 to each Count element in the sample above:

XDocument doc = XDocument.Parse (@"<FileExtensi ons>
<Extension>
<Name>.m4b</Name>
<Count>1</Count>
</Extension>
<Extension>
<Name>.docx</Name>
<Count>1</Count>
</Extension>
<Extension>
<Name>.doc</Name>
<Count>1</Count>
</Extension>
<Extension>
<Name>.xls</Name>
<Count>1</Count>
</Extension>
<Extension>
<Name>.xlsx</Name>
<Count>1</Count>
</Extension>
</FileExtensions> ");
foreach (XElement ext in doc.Root.Elemen ts("Extension") ) {
ext.SetElementV alue("Count", (int)ext.Elemen t("Count")
+ 1);
}
doc.Save(Consol e.Out);

HTH

--

Martin Honnen --- MVP XML

http://JavaScript.FAQTs.com/

[Edwin]

Re: Update an Existing Element Using Linq

I do not want to update every <Count></Countfor every extension. I just
want to udpate the <Count></Countonly if the <Name></Nameapplies for the
current extension being looked at.

For example:

<Extension>
<Name>.m4b</Name>
<Count>10</Count>
</Extension>
<Extension>
<Name>.docx</Name>
<Count>7</Count>
</Extension>
<Extension>
<Name>.doc</Name>
<Count>324</Count>
</Extension>
<Extension>
<Name>.xls</Name>
<Count>98</Count>
</Extension>
<Extension>
<Name>.xlsx</Name>
<Count>45</Count>
</Extension>
</FileExtensions>

[Martin Honnen]

Re: Update an Existing Element Using Linq

Edwin wrote:

I do not want to update every <Count></Countfor every extension. I
just want to udpate the <Count></Countonly if the <Name></Name>
applies for the current extension being looked at.

Well my code was just meant as an example.
Here is a different example that updates Count for one Extension element:

XDocument doc = XDocument.Parse (@"<FileExtensi ons>
<Extension>
<Name>.m4b</Name>
<Count>10</Count>
</Extension>
<Extension>
<Name>.docx</Name>
<Count>7</Count>
</Extension>
<Extension>
<Name>.doc</Name>
<Count>324</Count>
</Extension>
<Extension>
<Name>.xls</Name>
<Count>98</Count>
</Extension>
<Extension>
<Name>.xlsx</Name>
<Count>45</Count>
</Extension>
</FileExtensions> ");

string exampleExt = ".docx";
XElement extension = doc.Root.Elemen ts("Extension") .Where(e
=e.Element("Nam e").Value == exampleExt).Fir stOrDefault();
if (extension != null)
{
extension.SetEl ementValue("Cou nt", 1 +
(int)extension. Element("Count" ));
}
doc.Save(Consol e.Out);


--

Martin Honnen --- MVP XML

http://JavaScript.FAQTs.com/

[Edwin]

Re: Update an Existing Element Using Linq

Excellent! It worked!

I am not sure I understand it but it did exactly what I wanted it to do. I
now have to learn what exactly is happening.

Thanks for your help!

[Martin Honnen]

Re: Update an Existing Element Using Linq

Edwin wrote:

I am not sure I understand it but it did exactly what I wanted it to
do. I now have to learn what exactly is happening.

It is not that complicated, just uses LINQ to XML properties (like Root)
and methods (like Elements("Exten sion")) and LINQ queries with a lambda
expression:

string exampleExt = ".docx";
XElement extension = doc.Root.Elemen ts("Extension") .Where(e
=e.Element("Nam e").Value == exampleExt).Fir stOrDefault();
if (extension != null)
{
extension.SetEl ementValue("Cou nt", 1 +
(int)extension. Element("Count" ));
}

So doc.Root accesses the root element, doc.Root.Elemen ts("Extension" )
all "Extension" child elements of the Root. Then the LINQ Where method
filters those elements with the lambda expression
e =e.Element("Nam e").Value == exampleExt
meaning it takes those "Extension" elements which have a "Name" child
element where the Value is equal to exampleExt.

FirstOrDefault( ) simply means we want only the first of those filtered
elements or null if there is noone.

Once we have found an element all we need to do is set the value of the
"Count" child element using SetElementValue by incrementing the value by
one, to do that we can cast the "Count" child element to an int and add
1. That cast works as XElement provides

http://msdn.microsoft.com/en-us/library/system.xml.linq.xelement.op_explicit.aspx

to cast do a lot of CLR types.

--

Martin Honnen --- MVP XML

http://JavaScript.FAQTs.com/