Question

My XML file consists of a structure that resembles something like the following:

<root>
    <Manager name="1">
        <Manager name="2">
            <Employee name="3">
        </Manager>
        <Manager name="abe">
        </Manager>
        <Employee name="4">
        <Employee name="5">
    </Manager>
</root>

The XML feeds a treeview, and depending on where in the treeview a user clicks, I either want to retrieve the Employee clicked on (which is easy, as I can use treeview.SelectedNode), or otherwise in case the click was on the root node, or a manager node, the first employee under the manager.

I.e.

• Clicking on root should show details of Employee 4 (the first Employee record is directly under Manager 1 directly under root).
• Clicking on Manager 1 also should show Employee 4.
• Clicking Manager 2 should show Employee 3.
• Clicking Manager Abe yields no results.
• Employee 5 only shows when there is a click directly on that employee.

It could also be possible that Manager 1 does not have any direct employees under him. In that case, clicking on root should yield the first Employee under the first manager with employees. So if we assume Employee 4 and Employee 5 were not under Manager 1, clicking on root would yield Employee 3.

I tried using some different variants of Element, Elements, Descendant and Descendants, and am a bit stuck.

I suppose that I could write scenarios for every individual combination (I.e. rootClicked, managerClicked and employeeClicked), which is what I did originally, but I’m looking for something that will hopefully be easier to maintain, code-wise.

I had good hopes that using root.Element(“Employee”) would help, but that threw a Could not find an implementation of the query pattern for source type 'System.Xml.Linq.XEelement'. 'select' not found error.

Would anyone be able to supply me with that little nudge I need to solve my issue?

Answer 1

Using XPath:

ClickedNode.XPathEvaluate
    ("self::Employee | self::Manager/Employee[1] | self::root/Manager[1]/Employee[1]")

---

Update:

Answer to the edited question:

Use:

 ClickedNode[self::Employee]
|
 ClickedNode[not(self::Employee)]/descendant-or-self::Manager[Employee][1]/Employee[1]

This selects either:

a. The clicked node, if it is an `Employee’

Or:

b. The first child Employee of the first desendant-or-self of the clicked node, that is a manager and has a child Employee

And, if ClickedNode is an XElement (or XNode), then do:

  ClickedNode.XPathEvaluate
        (self::*[self::Employee]
      | self::node()[not(self::Employee)]
                       /descendant-or-self::Manager[Employee][1]/Employee[1]
        )

---

Finally, here is a complete C# code:

A static class named TestLinqXpath:

using System.Xml.Linq;
using System.Xml.XPath;

namespace TestLinqXpath
{
    public  static class TestLinqXpath
    {
        public static XElement SelectNearestDescendantEmployee(XElement clicked)
        {
            string Expr =
@"(self::*[self::Employee]
 | self::node()[not(self::Employee)]
           /descendant-or-self::Manager[Employee][1]/Employee[1]
   )";
            XElement result = clicked.XPathSelectElement(Expr);

            return result;
        }
    }
}

and extensive test:

using System;
using System.Xml.Linq;
using System.Xml.XPath;

namespace TestLINQ_Xml
{
    class Program
    {
        static void Main(string[] args)
        {
            Test();
        }

        static void Test()
        {
            string xml = 
@"<root>
    <Manager name='1'>
        <Manager name='2'>
            <Employee name='3'/>
        </Manager>
        <Manager name='abe'>
        </Manager>
        <Employee name='4'/>
        <Employee name='5'/>
    </Manager>
</root>";
            XElement top = XElement.Parse(xml);

            XElement cliked1 = top;
            XElement res1 = TestLinqXpath.TestLinqXpath.SelectNearestDescendantEmployee(cliked1);
            Console.WriteLine(res1.ToString());

            XElement cliked2 = top.XPathSelectElement("Manager[@name='1']");
            XElement res2 = TestLinqXpath.TestLinqXpath.SelectNearestDescendantEmployee(cliked2);
            Console.WriteLine(res2.ToString());

            XElement cliked3 = top.XPathSelectElement(".//Manager[@name='2']");
            XElement res3 = TestLinqXpath.TestLinqXpath.SelectNearestDescendantEmployee(cliked3);
            Console.WriteLine(res3.ToString());

            XElement cliked4 = top.XPathSelectElement(".//Manager[@name='abe']");
            XElement res4 = TestLinqXpath.TestLinqXpath.SelectNearestDescendantEmployee(cliked4);
            Console.WriteLine((res4 != null) ? res4.ToString() : "null");

            XElement cliked5 = top.XPathSelectElement(".//Employee[@name='5']");
            XElement res5 = TestLinqXpath.TestLinqXpath.SelectNearestDescendantEmployee(cliked5);
            Console.WriteLine(res5.ToString());
        }
    }
}

When this test is run, the wanted, correct results are produced:

<Employee name="4" />
<Employee name="4" />
<Employee name="3" />
null
<Employee name="5" />