I wrote a method to read XML and write information to an object. The XML contains elements with the information, but some of the information is encapsulated and I can't figure out how to get to the information out of it. The XML contains about 200 "results".
XML structure
<result id="xxxxx">
<name>Name</name>
<age>25</age>
<info>
<x>Some text</x>
<y>More Text</y>
</info>
</result>
Code
XDocument rootDocument = XDocument.Load(file);
var xy = from r in rootDocument.Descendants("result")
select new
{
Name = r.Element("name")
Age = r.Element("age"),
x = r.Element("info").Element("x"),
y = r.Element("info").Element("y"),
};
foreach (var r in xy)
{
Object o = new Object()
{
Name = r.Name,
Age = r.Age,
x = r.x,
y = r.y
};
}
Error
Object reference not set to an instance of an object.
The Error occurs at the line
x = r.Element("info")...
and the following one.
You could do the following:
var query = from r in rootDocument.Descendants("result")
select new
{
Name = (string)r.Element("name"),
Age = (int?)r.Element("age"),
x = (string)r.Elements("info").Elements("x").SingleOrDefault(),
y = (string)r.Elements("info").Elements("x").SingleOrDefault(),
};
var resultList = query.ToList();
Notes:
Once you have selected an XElement with a primitive value, you can convert the element to a c# primitive such as string or int? by using one of XElement's explicit casting operators, like so:
Name = (string)r.Element("name")
Age = (int?)r.Element("age")
The fact that you are seeing an Object reference not set to an instance of an object exception suggests that an element is unexpectedly missing. That could easily happen if one of the <result> elements were missing an <info> child element. The expression
r.Elements("info").Elements("x")
returns all child elements named <x> of child element(s) named <info>. Then SingleOrDefault() returns the only element of that sequence, or a default value if the sequence is empty. This protects against the situation when an <info> is missing.
Similarly, if the <age> element is missing, trying to cast it to int would throw a null reference exception since int is a value type. Casting to int? instead returns null instead of throwing the exception.
The final ToList() evaluates the query and returns the results in a list.
Sample fiddle.
Related
I have an xml schema like below
<library>
<book>
<id>1</id>
<name>abc</name>
<read>
<data>yes</data>
<num>20</num>
</read>
</book>
<book>
<id>20</id>
<name>xyz</name>
<read>
<data>yes</data>
<num>32</num>
</read>
</book>
</library>
Now if the id is 20 i need to take the value of tag <num> under <read>
I done the code as below
var xmlStr = File.ReadAllText("e_test.xml");
var str = XElement.Parse(xmlStr);
var result = str.Elements("book").Where(x => x.Element("id").Value.Equals("20")).ToList();
this give the whole <book> tag with id 20. From this how can I extract only the value of tag <num>.
ie is i need to get the value 32 in to a variable
Before you try to extract the num value, you need to fix your Where clause - at the moment you're comparing a string with an integer. The simplest fix - if you know that your XML will always have an id element which has a textual value which is an integer - is to cast the element to int.
Next, I'd use SingleOrDefault to make sure there's at most one such element, assuming that's what your XML document should have.
Then you just need to use Element twice to navigate down via read and then num, and cast the result to int again:
// Or use XDocument doc = ...; XElement book = doc.Root.Elements("book")...
XElement root = XElement.Load("e_test.xml")
XElement book = root.Elements("book")
.Where(x => (int) x.Element("id") == 20)
.SingleOrDefault();
if (book == null)
{
// No book with that ID
}
int num = (int) book.Element("read").Element("num");
If you're not dead set on using Linq, how about this XPath? XPath is probably more widely understood, and is really simple. The XPath to find your node would be:
/library/book[id=20]/read/num
Which you could use in C# thus:
var doc = new XmlDocument();
doc.LoadXml(myString);
var id = 20;
var myPath = "/library/book[id=" + id + "]/read/num";
var myNode = doc.SelectSingleNode(myPath);
Then you can do whatever you like with myNode to get its value etc..
Helpful reference:
http://www.w3schools.com/xsl/xpath_syntax.asp
I am trying to parse the xml below to load the id_name/rel_no pairs into an anonymous type collection. I am having a problem when looping through the collection and when element is missing in one of the elements. Is there a way not to load a particular pair when one of the elements id_name or rel_no is missing?
I get InvalidOperationException (sequence contains no elements) when the loop gets to that particular pair with missing element.
Thanks for any suggestions.
XDocument xdata = XDocument.Parse(data);
var query = from dox in xdata.Descendants("Inc")
select new
{
IDName= dox.Element("id_name").Value,
RelNo= dox.Descendants("rel_no").First().Value
};
XML
<Data>
<Inc>
<id_name>test</id_name>
<Relationships>
<Relationship>
<rel_no>004</rel_no>
</Relationship>
</Relationships>
</Inc>
<Inc>
<id_name>test2</id_name>
<Relationships>
<Relationship>
</Relationship>
</Relationships>
</Inc>
<Inc>
<id_name>test3</id_name>
<Relationships>
<Relationship>
<rel_no>006</rel_no>
</Relationship>
</Relationships>
</Inc>
</Data>
Accessing in a loop
foreach (var record in query)
{
}
var xdata = XDocument.Parse(data);
var items = xdata.Descendants("Inc")
.Select(d => new
{
DName = (string)d.Element("id_name"),
RelNo = ((string)d.Descendants("rel_no").FirstOrDefault() ?? "")
})
.ToList();
I have generated such xml file
<?xml version="1.0" encoding="utf-8"?>
<Requestes>
<Single_Request num="1">
<numRequest>212</numRequest>
<IDWork>12</IDWork>
<NumObject>21</NumObject>
<lvlPriority>2</lvlPriority>
<NumIn1Period>21</NumIn1Period>
</Single_Request>
</Requestes>
My aim is to get IDWork,numRequest and etc elements. I tried to get them this way:
foreach (XElement el in doc.Root.Elements())
{
if (el.Name == "Single_Request")
{
string num = el.Elements("numRequest").Value;
// but he says, that he cant do this .Value because it doest exist at all
}
}
How to fix this?
You have this error, because Elements("numRequest") returns collection of elements, not single element. You should use Element("numRequest") instead.
Also I suggest you to use query for getting elements by name instead of enumerating all elements and verifying their names:
var request = doc.Root.Element("Single_Request");
var num = (int)request.Element("numRequest");
Usually you use anonymous types or custom objects to group values parsed from xml:
var query = from r in doc.Root.Elements("Single_Request")
where (int)r.Attribute("num") == 1 // condition
select new {
NumRequest = (int)request.Element("numRequest"),
IdWork = (int)request.Element("IDWork"),
NumObject = (int)request.Element("NumObject")
};
var request = query.SinlgleOrDefault();
// use request.IdWork
I have an XML document that contains a series of item nodes that look like this:
<data>
<item>
<label>XYZ</label>
<description>lorem ipsum</description>
<parameter type="id">123</parameter>
<parameter type="name">Adam Savage</parameter>
<parameter type="zip">90210</parameter>
</item>
</data>
and I want to LINQ it into an anonymous type like this:
var mydata =
(from root in document.Root.Elements("item")
select new {
label = (string)root.Element("label"),
description = (string)root.Element("description"),
id = ...,
name = ...,
zip = ...
});
What's the best way to pull each parameter type according to the value of its 'type' attribute? Since there are many parameter elements you wind up with root.Elements("parameter") which is a collection. The best way I can think to do it is like this by method below but I feel like there must be a better way?
(from c in root.Descendants("parameter") where (string)c.Attribute("type") == "id"
select c.Value).SingleOrDefault()
I would use the built-in query methods in LINQ to XML instead of XPath. Your query looks fine to me, except that:
If there are multiple items, you'd need to find the descendants of that instead; or just use Element if you're looking for direct descendants of the item
You may want to pull all the values at once and convert them into a dictionary
If you're using different data types for the contents, you might want to cast the element instead of using .Value
You may want to create a method to return the matching XElement for a given type, instead of having several queries.
Personally I don't think I'd even use a query expression for this. For example:
static XElement FindParameter(XElement element, string type)
{
return element.Elements("parameter")
.SingleOrDefault(p => (string) p.Attribute("type") == type);
}
Then:
var mydata = from item in document.Root.Elements("item")
select new {
Label = (string) item.Element("label"),
Description = (string) item.Element("description"),
Id = (int) FindParameter(item, "id"),
Name = (string) FindParameter(item, "name"),
Zip = (string) FindParameter(item, "zip")
};
I suspect you'll find that's neater than any alternative using XPath, assuming I've understood what you're trying to do.
use XPATH - it is very fast ( except xmlreader - but a lot of if's)
using (var stream = new StringReader(xml))
{
XDocument xmlFile = XDocument.Load(stream);
var query = (IEnumerable)xmlFile.XPathEvaluate("/data/item/parameter[#type='id']");
foreach (var x in query.Cast<XElement>())
{
Console.WriteLine( x.Value );
}
}
Load function is already defined in xmlData class
public class XmlData
{
public void Load(XElement xDoc)
{
var id = xDoc.XPathSelectElements("//ID");
var listIds = xDoc.XPathSelectElements("/Lists//List/ListIDS/ListIDS");
}
}
I'm just calling the Load function from my end.
XmlData aXmlData = new XmlData();
string input, stringXML = "";
TextReader aTextReader = new StreamReader("D:\\test.xml");
while ((input = aTextReader.ReadLine()) != null)
{
stringXML += input;
}
XElement Content = XElement.Parse(stringXML);
aXmlData.Load(Content);
in load function,im getting both id and and listIds as null.
My test.xml contains
<SEARCH>
<ID>11242</ID>
<Lists>
<List CURRENT="true" AGGREGATEDCHANGED="false">
<ListIDS>
<ListID>100567</ListID>
<ListID>100564</ListID>
<ListID>100025</ListID>
<ListID>2</ListID>
<ListID>1</ListID>
</ListIDS>
</List>
</Lists>
</SEARCH>
EDIT: Your sample XML doesn't have an id element in the namespace with the nss alias. It would be <nss:id> in that case, or there'd be a default namespace set up. I've assumed for this answer that in reality the element you're looking for is in the namespace.
Your query is trying to find an element called id at the root level. To find all id elements, you need:
var tempId = xDoc.XPathSelectElements("//nss:id", ns);
... although personally I'd use:
XDocument doc = XDocument.Parse(...);
XNamespace nss = "http://schemas.microsoft.com/SQLServer/reporting/reportdesigner";
// Or use FirstOrDefault(), or whatever...
XElement idElement = doc.Descendants(nss + "id").Single();
(I prefer using the query methods on LINQ to XML types instead of XPath... I find it easier to avoid silly syntax errors etc.)
Your sample code is also unclear as you're using xDoc which hasn't been declared... it helps to write complete examples, ideally including everything required to compile and run as a console app.
I am looking at the question 3 hours after it was submitted and 41 minutes after it was (last) edited.
There are no namespaces defined in the provided XML document.
var listIds = xDoc.XPathSelectElements("/Lists//List/ListIDS/ListIDS");
This XPath expression obviously doesn't select any node from the provided XML document, because the XML document doesn't have a top element named Lists (the name of the actual top element is SEARCH)
var id = xDoc.XPathSelectElements("//ID");
in load function,im getting both id and and listIds as null.
This statement is false, because //ID selects the only element named ID in the provided XML document, thus the value of the C# variable id is non-null. Probably you didn't test thoroughly after editing the XML document.
Most probably the original ID element belonged to some namespace. But now it is in "no namespace" and the XPath expression above does select it.
string xmldocument = "<response xmlns:nss=\"http://schemas.microsoft.com/SQLServer/reporting/reportdesigner\"><action>test</action><id>1</id></response>";
XElement Content = XElement.Parse(xmldocument);
XPathNavigator navigator = Content.CreateNavigator();
XmlNamespaceManager ns = new XmlNamespaceManager(navigator.NameTable);
ns.AddNamespace("nss", "http://schemas.microsoft.com/SQLServer/reporting/reportdesigner");
var tempId = navigator.SelectSingleNode("/id");
The reason for the null value or system returned value is due to the following
var id = xDoc.XPathSelectElements("//ID");
XpathSElectElements is System.xml.linq.XElment which is linq queried date. It cannot be directly outputed as such.
To Get individual first match element
use XPathSelectElement("//ID");
You can check the number of occurrences using XPathSelectElements as
var count=xDoc.XPathSelectElements("//ID").count();
you can also query the linq statement as order by using specific conditions
Inorder to get node value from a list u can use this
foreach (XmlNode xNode in xDoc.SelectNodes("//ListIDS/ListID"))
{
Console.WriteLine(xNode.InnerText);
}
For Second list you havnt got the value since, the XPath for list items is not correct