Develop Reference

Sequence contains no elements when trying to grab xml node value from xml string

Please read the code bellow. There I am trying to grab all elements under the <GetSellerListResponse> node, then my goal is to grab TotalNumberOfPages value (currently it's 9 as you can see in the XML).
But my problem is I am getting an error:
System.InvalidOperationException: 'Sequence contains no elements'
Error screenshot is attached for better understanding. Can you tell me what's wrong the way I am trying to grab all elements? Also if possible can you tell how I can grab that 9 from TotalNumberOfPage?
Thanks in advance
C#:
var parsedXML = XElement.Parse(xml);
var AllElements = parsedXML.Descendants("GetSellerListResponse")
.Where(x => x.Attribute("xmlns").Value.Equals("urn:ebay:apis:eBLBaseComponents"))
.First();
XML:
<?xml version="1.0" encoding="UTF-8"?>
<GetSellerListResponse xmlns="urn:ebay:apis:eBLBaseComponents">
<Timestamp>2018-06-20T17:26:29.518Z</Timestamp>
<Ack>Success</Ack>
<Version>1059</Version>
<Build>E1059_CORE_APISELLING_18694654_R1</Build>
<PaginationResult>
<TotalNumberOfPages>9</TotalNumberOfPages>
</PaginationResult>
</GetSellerListResponse>

EDIT: your mistake is the usage of XElement: it is searching for matching elements in the children of <GetSellerListResponse>; that's why you are not getting any result. Change XElement.Parse(xml); to XDocument.Parse(xml);, then the following snippets will work.
You could simply check for the local name:
var AllElements = parsedXML.Descendants().First(x => x.Name.LocalName == "GetSellerListResponse");
I would suggest to use XDocument instead of XElement for parsedXML, because you could shorten the above query to var AllElements = parsedXML.Root;
Another thing you could try is prepending the namespace:
XNamespace ns = "urn:ebay:apis:eBLBaseComponents";
var AllElements = parsedXML.Descendants(ns + "GetSellerListResponse").First();
To answer the question "how to get the number of pages":
var pages = AllElements.Element(ns + "PaginationResult").Element(ns + "TotalNumberOfPages").Value;

I would suggest using the XmlDocument class from System.Xml.
Try the code below:
XmlDocument doc = new XmlDocument();
doc.LoadXml("<GetSellerListResponse xmlns=\"urn:ebay:apis:eBLBaseComponents\"><Timestamp>2018-06-20T17: 26:29.518Z</Timestamp><Ack>Success</Ack><Version>1059</Version><Build>E1059_CORE_APISELLING_18694654_R1</Build><PaginationResult><TotalNumberOfPages>9</TotalNumberOfPages></PaginationResult></GetSellerListResponse>");
XmlNodeList nodeList = doc.GetElementsByTagName("TotalNumberOfPages");
In this case, your nodeList will have just the one element for TotalNumberOfPages and you can access the value by checking
nodeList.FirstOrDefault().InnerText

I'm unable to extract the Data from this XML

I'm currently working on a small weather application in C#. To do this, I need to extract data from this xml file: http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22london%22&format=xml
In this specific case I need the value of the first /query/results/place/woeid node. I've been looking around and tried many different methods, but didn't manage to get any values with any of those. My current code looks like this:
string query = String.Format("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22london%22&format=xml");
XmlDocument xml = new XmlDocument();
xml.Load(query);
XmlNodeList nodeList = wData.DocumentElement.SelectNodes("/query/results/place");
foreach (XmlNode node in nodeList)
{
return node.SelectSingleNode("woeid").InnerText;
}
return "NO WOEID FOUND!";
I'm just starting to learn C# so I might do some stupid mistakes. Still, I would really appreciate any kind of help.

You can use XDocument
string query = String.Format("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22london%22&format=xml");
XDocument xml = XDocument.Load(query);
XNamespace ns = "http://where.yahooapis.com/v1/schema.rng";
var woeid = xml.Element("query").Element("results").Elements(ns + "place").FirstOrDefault().Element(ns +"woeid").Value;
Make sure you check if there are any elements in the XDocuments

Navigating using XPath stored as a string

I am trying to store XPath of an XML attribute as a string in a separate file so that if XPath changes, I can easily modify the navigation to the attribute without changing code.
For example, in following XML:
<Result>
<Server = "main">
<Client id="1"></Client>
</Server>
</Result>
if I want to navigate to id attribute of Client element, I can have following string:
Result->Server->Client->id
I am not sure how in C# I can navigate using this string form of XPath and then, read the attribute value from the target XML.
Please help.
Harit

Well, firstly, your XML is a bit strange, with
<Server = "main">
Do you mean
<Server id="main">
But, regardless of that, you could just store the XPath directly instead of your string version. Like:
/Result/Server/Client[0]/#id
then you read the string from the file and pass it into something like:
public string GetClientIdString(string xPathString)
{
var doc = new XmlDocument();
doc.Load("SomeXml.xml");
return doc.DocumentElement.SelectSingleNode(xPathString).Value;
}
The issue becomes that you can't really store the XPath exactly how you would like if you plan on having more than one Client under Server. If you need that functionality, though, you could parse out your version of the XPath and do something like:
public IEnumerable<string> GetClientIdStrings(string elementXPath, string attribute)
{
var doc = new XmlDocument();
doc.Load(SomeXml.xml);
var clientIdStrings = new List<string>();
foreach(var node in doc.DocumentElement.SelectNodes(elementXPath))
{
clientIdStrings.Add(node.Attributes[attribute].Value);
}
return clientIdStrings;
}

How to parse the below xml string in c#

I have the below xml string in one string variable.
string xmlString = "<a:ORegions>
<a:ID>1</a:ID>
<a:regionCode>US</a:regionCode>
</a:ORegions>
<a:ORegions>
<a:ID>2</a:ID>
<a:regionCode>CANADA</a:regionCode>
</a:ORegions>
<a:ORegions>
<a:ID>3</a:ID>
<a:regionCode>ASIA</a:regionCode>
</a:ORegions>
Now i want to access regionCode values, that is US, CANADA, ASIA
How i can do that using c#. I am new to xml parsing.

You can deserialize that string (assuming you fix the various syntax errors) via the System.Xml namespace classes, particularly XmlDocument, such as with its Load method. To access the namespaces (a in a:Oregions and such is a namespace), you'll want an XmlNamespaceManager. You'd then register the namespaces (they must be defined somewhere) with the manager and use that when querying the XmlDocument.

Use LinqToXml
var doc = XDocument.Parse(xmlString);
You can then access elements, values and attributes within:
XNamespace xmlNamespace = "a";
//e.g. Retrieve's a list of regioncodes...
var ids = doc.Elements(xmlNamespace + "ORegions")
.Select(r => r.Element("regionCode").Value);

XmlDocument document = new XmlDocument();
document.Load(filePath);
foreach (XmlNode node in document.GetElementsByTagName("a:regionCode"))
Console.WriteLine(node.InnerText);

Selecting XML nodes?

I have a large XML file with a lot of these file nodes:
<File>
<Component>Main</Component>
<Path>C:\Logs\Main</Path>
<FileName>logfile1.log</FileName>
</File>
In my C# program I want to select a node with a certain file name, eg in the above example I would like to select the File node where the FileName is logfile1.log. Is there a way I can do this in my C#, or maybe I need to make the FileName as an attribute for each File node, e.g.:
<File name="logfile1.log">...</File>
Could anybody advise me on the best practise here? Thanks for any help!

Using query syntax;
var xml = XDocument.Load("input.xml");
var node = (from file in xml.Descendants("File")
where (string)file.Element("FileName") == "logfile1.log"
select file).Single();
Obviously the call to force the query (Single() in this case) should be swapped out to suit your own app.

XPath query would be a good choice for that. You can use xpath to search for either an element name or an attribute name.
something like:
var doc = new XPathDocument(path);
var xpath = doc.CreateNavigator();
//with element
var node = xpath.SelectSingleNode("//File[FileName='logfile1.log']");
//or with attribute
var node = xpath.SelectSingleNode("//File[#name='logfile1.log']");
Or, if there could be more than one you can use Select to find multiple matches and then iterate them.
var node = xpath.Select("//File...");

var doc = new XmlDocument();
doc.LoadXml(xml); // or Load(path)
var node = doc.SelectSingleNode("//File/FileName[.='logfile1.log']");
(see XPath selection by innertext)
or
var doc = XDocument.Load(path);
var node = doc.Elements("Path").FirstOrDefault(e => (string)e.Element("FileName") == "logfile1.log");