How to: Find Preceding Siblings (XPath-LINQ to XML)

This topic compares the XPath preceding-sibling axis to the LINQ to XML child System.Xml.Linq.XNode.ElementsBeforeSelf axis.

The XPath expression is:

preceding-sibling::*

Note that the results of both XPathSelectElements and System.Xml.Linq.XNode.ElementsBeforeSelf are in document order.

Example

The following example finds the FullAddress element, and then retrieves the previous elements using the preceding-sibling axis.

This example uses the following XML document: Sample XML File: Customers and Orders (LINQ to XML).

XElement co = XElement.Load("CustomersOrders.xml");

XElement add = co.Element("Customers").Element("Customer").Element("FullAddress");

// LINQ to XML query
IEnumerable<XElement> list1 = add.ElementsBeforeSelf();

// XPath expression
IEnumerable<XElement> list2 = add.XPathSelectElements("preceding-sibling::*");

if (list1.Count() == list2.Count() &&
        list1.Intersect(list2).Count() == list1.Count())
    Console.WriteLine("Results are identical");
else
    Console.WriteLine("Results differ");
foreach (XElement el in list2)
    Console.WriteLine(el);

Dim co As XElement = XElement.Load("CustomersOrders.xml")
Dim add As XElement = co.<Customers>.<Customer>. _
        <FullAddress>.FirstOrDefault

' LINQ to XML query
Dim list1 As IEnumerable(Of XElement) = add.ElementsBeforeSelf()

' XPath expression
Dim list2 As IEnumerable(Of XElement) = add.XPathSelectElements("preceding-sibling::*")

If list1.Count() = list2.Count() And _
        list1.Intersect(list2).Count() = list1.Count() Then
    Console.WriteLine("Results are identical")
Else
    Console.WriteLine("Results differ")
End If
For Each el As XElement In list2
    Console.WriteLine(el)
Next

This example produces the following output:

Results are identical
<CompanyName>Great Lakes Food Market</CompanyName>
<ContactName>Howard Snyder</ContactName>
<ContactTitle>Marketing Manager</ContactTitle>
<Phone>(503) 555-7555</Phone>

See Also

Concepts

LINQ to XML for XPath Users

Build Date:

2012-08-02