C# Linq to XML check if element exists

Question

I have an XML document as follows:

<Database>
 <SMS>
   <Number>"+447528349828"</Number> 
   <Date>"09/06/24</Date> 
   <Time>13:35:01"</Time> 
   <Message>"Stop"</Message> 
 </SMS>
 <SMS>
   <Number>"+447528349828"</Number> 
   <Date>"09/06/24</Date> 
   <Time>13:35:01"</Time> 
   <Message>"Stop"</Message> 
 </SMS>
</Database>

I am trying to check whether the number child node of the parent SMS node exists in the document (for validation purposes to avoid inserting duplicate data).

Any advice on a potential solution?

EDIT: The element will be compared to an input string. For example if(inputNumber == xmlDocNumber){ //Don't Insert New Element }

Answer 1

I'll suggest a slightly different tack to using Count() - use Any(). The advantage is that Any() can stop as soon as it gets any matches at all:

var smsWithNoNumber = main.Descendants("SMS")
                          .Where(x => !x.Elements("Number").Any());

In this case it won't make much odds, but in cases where Count() might have to count a million hits just to tell you that there was at least one, it's a useful trick to know. I'd say it's also a clearer indicator of what you mean.

Answer 2

You could apply an XSL document that translates the data by looping through the SMS nodes and excluding any that has a duplicate Number/text() value

Check would be something like:

<xsl:template match="SMS">
<xsl:variable name="parentNode" select="." />
<xsl:if test="preceding-sibling::SMS/Number/text()=$parentNode/Number/text()">
.....include a copy of node......
</xsl:if>
  </xsl:template>

Answer 3

Assuming that you have your number in some canonicalized form and your XML is loaded into an XmlDocument or some such, the simplest non-LINQ way to do it is with an XPath query:

string pattern = String.Format("/Database/SMS/Number[. = '{0}']", number);
if (myDoc.SelectSingleNode(pattern) != null)
{
   // number already exists in document
}