如何添加ISortedEnumerable <XElement> 到XElement？

Question

I'm trying to sort XElement's children using Linq and then replace existing children with sorted.

First I create XElement:

XElement WithLinq =
            new XElement("Names",
                from cust in Customers.AsEnumerable()
                select
                    new XElement("Customer",
                        new XAttribute("ID", cust.ID),
                        new XElement("Name", cust.Name),
                        new XElement("Purchases",
                        from pur in cust.Purchases
                        select
                            new XElement("Purchase",
                                new XElement("Produkt",pur.Description),
                                new XAttribute("ID",pur.ID),
                                new XElement("Price",pur.Price),
                                new XComment("teraz daty"),
                                new XElement("Date",pur.Date), //Formatuje DateTime zgodnie z normami XMLa
                                new XElement("DataAleNieDoKonca",pur.Date.ToString(CultureInfo.InvariantCulture)))))    
                        );

Then I sort Nodes:

var NowaKolejnosc = WithLinq.Elements().Last().Elements().OrderBy(n => n.Name).ThenBy(n => n.Value);

And replace them:

WithLinq.Elements().Last().ReplaceNodes(NowaKolejnosc);

But I get a runtime exception: ArgumentException: 'Co najmniej jeden obiekt musi implementować element IComparable.' Translation: At least one object must implement IComparable.

I don't understand what is causing an exception and how to fix it.

Answer 1

The error is occurring because XElement.Name is of type System.Xml.Linq.XName . XName does not implement IComparable .

XName wraps a System.String value and it overrides ToString to return that System.String value.

Since System.String implements IComparable we can leverage this knowledge to invoke OrderBy correctly and successfully. This has the desired semantics because, logically, we want to compare the wrapped strings.

WithLinq.Elements().Last().Elements().OrderBy(n => n.Name.ToString()).ThenBy(n => n.Value)

When using multiple ordering LINQ operators, I find it much more readable to use the query expression syntax.

from element in WithLinq.Elements().Last().Elements()
orderby element.Name.ToString(), element.Value
select element

Answer 2

This is a comment to build on the accepted answer by Aluan Haddad.

Suggestion: consider using XName.LocalName in place of XName.ToString() :

Working directly with the element.Name.LocalName property may be suitable, provided that the XML does not use namespaces or the namespaces in the XML are not needed for a specific operation.

When processing large (> 1GB) XML files, I've found moderate performance gains by swapping XName.ToString() for XName.LocalName .

Albeit anecdotally, this change saved around a half-dozen minutes on a 1 hour long program that required repeated sorts and comparisons. In other contexts, YMMV.

For some context, here are the differences via the reference source :

/// <summary>
/// Returns the expanded XML name in the format: {namespaceName}localName.
/// </summary>
public override string ToString() {
    if (ns.NamespaceName.Length == 0) return localName;
    return "{" + ns.NamespaceName + "}" + localName;
}

/// <summary>
/// Gets the local (unqualified) part of the name.
/// </summary>
/// <seealso cref="XName.Namespace"/>
public string LocalName {
    get { return localName; }
}