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LINQ to XML axes overview - LINQ to XML
Use axis methods from the XElement, XDocument, and IEnumerable classes to find elements in an XML tree and retrieve their values.
07/20/2015
516792fb-461d-40a8-8a50-9993a51258fc

LINQ to XML axes overview

After you've created an XML tree or loaded an XML document into an XML tree, you can query it to find elements and attributes and retrieve their values. You retrieve collections through the axis methods, also called axes. Some of the axes are methods in the xref:System.Xml.Linq.XElement and xref:System.Xml.Linq.XDocument classes that return xref:System.Collections.Generic.IEnumerable%601 collections. Some of the axes are extension methods in the xref:System.Xml.Linq.Extensions class. The axes that are implemented as extension methods operate on collections and return collections.

As described in XElement class overview, an xref:System.Xml.Linq.XElement object represents a single element node. The content of an element can be complex (sometimes called structured content), or it can be a simple element. A simple element can be empty or can contain a value. If the node contains structured content, you can use the various axis methods to retrieve enumerations of descendant elements. The most commonly used axis methods are xref:System.Xml.Linq.XContainer.Elements%2A and xref:System.Xml.Linq.XContainer.Descendants%2A.

In addition to the axis methods, which return collections, there are two more methods that you'll commonly use in LINQ to XML queries. The xref:System.Xml.Linq.XContainer.Element%2A method returns a single xref:System.Xml.Linq.XElement. The xref:System.Xml.Linq.XElement.Attribute%2A method returns a single xref:System.Xml.Linq.XAttribute.

For many purposes, LINQ queries provide the most powerful way to examine a tree, extract data from it, and transform it. LINQ queries operate on objects that implement xref:System.Collections.Generic.IEnumerable%601, and the LINQ to XML axes return xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement collections, and xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XAttribute collections. You need these collections to do your queries.

In addition to the axis methods that retrieve collections of elements and attributes, there are axis methods that allow you to iterate through the tree in great detail. For example, instead of dealing with elements and attributes, you can work with the nodes of the tree. Nodes are a finer level of granularity than elements and attributes. When working with nodes, you can examine XML comments, text nodes, processing instructions, and more. This functionality is important, for example, to someone who is writing a word processor and wants to save documents as XML. However, the majority of XML programmers are primarily concerned with elements, attributes, and their values.

Methods for retrieving a collection of elements

The following is a summary of the methods of the xref:System.Xml.Linq.XElement class (or its base classes) that you call on an xref:System.Xml.Linq.XElement to return a collection of elements.

Method Description
xref:System.Xml.Linq.XNode.Ancestors%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the ancestors of this element. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the ancestors that have the specified xref:System.Xml.Linq.XName.
xref:System.Xml.Linq.XContainer.Descendants%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the descendants of this element. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the descendants that have the specified xref:System.Xml.Linq.XName.
xref:System.Xml.Linq.XContainer.Elements%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the child elements of this element. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the child elements that have the specified xref:System.Xml.Linq.XName.
xref:System.Xml.Linq.XNode.ElementsAfterSelf%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the elements that come after this element. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the elements after this element that have the specified xref:System.Xml.Linq.XName.
xref:System.Xml.Linq.XNode.ElementsBeforeSelf%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the elements that come before this element. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the elements before this element that have the specified xref:System.Xml.Linq.XName.
xref:System.Xml.Linq.XElement.AncestorsAndSelf%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of this element and its ancestors. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the elements that have the specified xref:System.Xml.Linq.XName.
xref:System.Xml.Linq.XElement.DescendantsAndSelf%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of this element and its descendants. An overload returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XElement of the elements that have the specified xref:System.Xml.Linq.XName.

Method for retrieving a single element

The following method retrieves a single child from an xref:System.Xml.Linq.XElement object.

Method Description
xref:System.Xml.Linq.XContainer.Element%2A?displayProperty=nameWithType Returns the first child xref:System.Xml.Linq.XElement object that has the specified xref:System.Xml.Linq.XName.

Method for retrieving a collection of attributes

The following method retrieves attributes from an xref:System.Xml.Linq.XElement object.

Method Description
xref:System.Xml.Linq.XElement.Attributes%2A?displayProperty=nameWithType Returns an xref:System.Collections.Generic.IEnumerable%601 of xref:System.Xml.Linq.XAttribute of all of the attributes.

Method for retrieving a single attribute

The following method retrieves a single attribute from an xref:System.Xml.Linq.XElement object.

Method Description
xref:System.Xml.Linq.XElement.Attribute%2A?displayProperty=nameWithType Returns the xref:System.Xml.Linq.XAttribute that has the specified xref:System.Xml.Linq.XName.