I'm working with an existing XML document which has a structure (in part) like so:
<Group>
<Entry>
<Name> Bob </Name>
<ID> 1 </ID>
</Entry>
<Entry>
<Name> Larry </Name>
</Entry>
</Group>
I'm using LINQ to XML to query the XDocument to retrieve all these entries as follows:
var items = from g in xDocument.Root.Descendants("Group").Elements("Entry")
select new
{
name = (string)g.element("Name").Value,
id = g.Elements("ID").Count() > 0 ? (string)g.Element("ID").Value : "none"
};
The "ID" elements aren't always there and so my solution to this was the Count() jazz above. But I'm wondering if someone has a better way to do this. I'm still getting comfortable with this new stuff and I suspect that there may be a better way to do this than how I'm currently doing it.
Is there a better/more preferred way to do what I want?
XElement actually has interesting explicit conversion operators that do the right thing in this case.
So, you rarely actually need to access the .Value property.
This is all you need for your projection:
var items =
from g in xDocument.Root.Descendants("Group").Elements("Entry")
select new
{
name = (string) g.Element("Name"),
id = (string) g.Element("ID") ?? "none",
};
And if you'd prefer to use the value of ID as an integer in your anonymous type:
var items =
from g in xDocument.Root.Descendants("Group").Elements("Entry")
select new
{
name = (string) g.Element("Name"),
id = (int?) g.Element("ID"),
};
In a similar situation I used an extension method:
public static string OptionalElement(this XElement actionElement, string elementName)
{
var element = actionElement.Element(elementName);
return (element != null) ? element.Value : null;
}
usage:
id = g.OptionalElement("ID") ?? "none"
How about:
var items = from g in xDocument.Root.Descendants("Group").Elements("Entry")
let idEl = g.Element("ID")
select new
{
name = (string)g.element("Name").Value,
id = idEl == null ? "none" : idEl.Value;
};
if this barfs, then FirstOrDefault() etc might be useful, else just use an extension method (as already suggested).
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 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 the following xml:
<?xml version="1.0" encoding="utf-8" ?>
<layout>
<menu name="Employees" url="Employees.aspx" admin="0">
</menu>
<menu name="Projects" url="Projects.aspx" admin="1">
</menu>
<menu name="Cases" url="Cases.aspx" admin="1">
</menu>
<menu name="CaseView" url="CaseView.aspx" admin="1" hidden="1" parent="Projects">
</menu>
<menu name="Management" url="" admin="1">
<item name="Groups" url="Groups.aspx" admin="1" parent="Management"/>
<item name="Statuses" url="Statuses.aspx" admin="1"/>
</menu>
</layout>
Here I have CaseView and Groups that both have a 'parent' attribute.
Currently I iterate like this:
IEnumerable<XElement> menus =
doc.Element("layout").Elements();
foreach (var menu in menus)
{
string name = menu.Attribute("name").Value;
string active = "";
string url = menu.Attribute("url").Value;
if(activePage == url)
{
active = "class=\"active\"";
}
...
What I want is:
if(activePage == url || ActiveIsChildOf(name, activePage))
{
active = "class=\"active\"";
}
Essentially this method needs to find if an element with activePage as its url attribute exists. If it does, see if it has a parent attribute; if it does, check if the parent == name.
Is there some way to find an element by attribute or something?
ex:
XElement e = doc.GetByAttribute("url",activePage)
Thanks
Since you are using Linq to XML, you can use Descendants method - it returns all child elements, not just the direct children. After that, you can use LINQ to filter the results.
XDocument doc;
string activePage;
var activeMenu = doc.Descendants("menu")
.FirstOrDefault(o => o.Attribute("url").Value == activePage);
You might need to check if o.Attribute("url") does not return null (it does when the attribute does not exist) if you cannot guarantee that the source XML does not have such attribute for all menu elements.
You can also skip the argument to Descendants() to check all elements - in your sample data that would allow you to check both menu and item elements. For example:
var activeMenu = doc.Descendants()
.Where(o => o.Name == "menu" || o.Name == "item")
.FirstOrDefault(o => o.Attribute("url").Value == activePage);
If xpath is too cryptic, you can use LINQ:
IEnumerable<XElement> hits =
(from el in XMLDoc.root.Elements("item")
where (string)el.Attribute("url") == activePage
select el);
or like this:
XElement xml = XElement.Load(file);
XElement xele = xml.Elements("item").FirstOrDefault(e => ((string)e.Attribute("url")) == activePage);
if(null != xele )
{
// do something with it
}
And you probably want it case-insensitive:
XElement xml = XElement.Load(file);
XElement xele = xml.Elements("item").FirstOrDefault(e => StringComparer.OrdinalIgnoreCase.Equals((string)e.Attribute("url") , activePage));
if(null != xele )
{
// do something with it
}
If you want both menu and item, use this:
XElement xml = XElement.Load(file);
XElement xele = xml.Elements().FirstOrDefault(e => StringComparer.OrdinalIgnoreCase.Equals((string)e.Attribute("url") , activePage));
if(null != xele )
{
// do something with it
}
You can simply use xPath. It's a query language for XML.
You can formulate something like this :
var xDoc = new XmlDocument();
xDoc.Load("XmlFile.xml");
//Fetch your node here
XmlNode = xDoc.SelectSingleNode(/layout/menu[#url='activepage'][1]);
It returns a set of node and the index 1 is to get the first node of the given set.
You can always use xDoc.SelectNodes if you want all the matching nodes.
Since you are using LINQ you can simply include System.Xml.XPath and select nodes with XPathSelectElement or XPathSelectElements.
You can do that with XPath:
doc.SelectNodes("//*[#url='" + activePage + "']")
It will return all document items that have activePage as url attribute.
A case insensitive search example, converting xml to a dictionary:
Dim expandos = XDocument.Parse(Request("Xml")).Root.Elements.Select(
Function(e)
Dim expando As Object = New ExpandoObject,
dic = e.Attributes.ToDictionary(Function(a) a.Name.LocalName, Function(a) a.Value,
StringComparer.InvariantCultureIgnoreCase)
expando.PedidoId = dic("PedidoId")
expando.FichaTecnicaModeloId = dic("FichaTecnicaModeloId")
expando.Comodo = dic("Comodo")
expando.Cliente = dic("Cliente")
Return expando
End Function)
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 );
}
}
I'm having trouble trying to update my xml file with a new value. I have a class Person, which only contains 2 strings, name and description. I populate this list and write it as an XML file. Then I populate a new list, which contains many of the same names, but some of them contains descriptions that the other list did not contain. How can I check if the name in the current XML file contains a value other than "no description", which is the default for "nothing"?
Part of the xml file:
<?xml version="1.0" encoding="utf-8"?>
<Names>
<Person ID="2">
<Name>Aaron</Name>
<Description>No description</Description>
</Person>
<Person ID="2">
<Name>Abdi</Name>
<Description>No description</Description>
</Person>
</Names>
And this is the method for writing the list to the xml file:
public static void SaveAllNames(List<Person> names)
{
XDocument data = XDocument.Load(#"xml\boys\Names.xml");
foreach (Person person in names)
{
XElement newPerson = new XElement("Person",
new XElement("Name", person.Name),
new XElement("Description", person.Description)
);
newPerson.SetAttributeValue("ID", GetNextAvailableID());
data.Element("Names").Add(newPerson);
}
data.Save(#"xml\boys\Names.xml");
}
In the foreach loop how do I check if the person's name is already there, and then check if the description is something other than "no description", and if it is, update it with the new information?
I'm not sure I understand properly what you want, but I'm assuming you want to update the description only when the name is already there and the description is currently No description (which you should probably change to an empty string, BTW).
You could put all the Persons into a Dictionary based by name:
var doc = …;
var persons = doc.Root.Elements()
.ToDictionary(x => (string)x.Element("Name"), x => x);
and then query it:
if (persons.ContainsKey(name))
{
var description = persons[name].Element("Description");
if (description.Value == "No description")
description.Value = newDescription;
}
That is, if you care about performance. If you don't, you don't need the dictionary:
var person = doc.Root.Elements("Person")
.SingleOrDefault(x => (string)x.Element("Name") == name);
if (person != null)
{
var description = person.Element("Description");
if (description.Value == "No description")
description.Value = newDescription;
}
You can use the Nodes-Method on XElement and check manually.
But i will advise you to use the XPathEvaluate-Extension Method
For XPath expression take a look at:
How to check if an element exists in the xml using xpath?
I think you could create a peoplelist which only contains people not in the xml.
like ↓
var containlist = (from p in data.Descendants("Name") select p.Value).ToList();
var result = (from p in peoplelist where !containlist.Contains(p.Name) select p).ToList();
so that , you would no need to change anything with your exist method ...
just call it after..
SaveAllNames(result);