Best way to compare XElement objects
I had an issue comparing XElements for equality where one of the elements had child nodes that where self closing tags but the other had the open and close tags, e.g. [blah/] vs [blah][/blah]
The deep equals function was of course reporting them to be different so I needed a normalise function. I ended up using a variant of what is posted in this blog (by "marianor"):
http://weblogs.asp.net/marianor/archive/2009/01/02/easy-way-to-compare-two-xmls-for-equality.aspx
A minor change being that I use the deep equals function after normalising (rather than string compare) and also I added logic to treat elements that contain empty text the same as empty elements (to resolve the afore mentioned issue). The result is below.
private bool CompareXml(string xml)
{
var a = Normalize(currentElement);
var b = Normalize(newElement);
return XElement.DeepEquals(a, b);
}
private static XElement Normalize(XElement element)
{
if (element.HasElements)
{
return new XElement(element.Name, element.Attributes().Where(a => a.Name.Namespace == XNamespace.Xmlns)
.OrderBy(a => a.Name.ToString()),element.Elements().OrderBy(a => a.Name.ToString())
.Select(e => Normalize(e)));
}
if (element.IsEmpty || string.IsNullOrEmpty(element.Value))
{
return new XElement(element.Name, element.Attributes()
.OrderBy(a => a.Name.ToString()));
}
return new XElement(element.Name, element.Attributes()
.OrderBy(a => a.Name.ToString()), element.Value);
}
I found this excellent article useful. It contains a code sample that implements an alternative to XNode.DeepEquals that normalises the XML trees before comparison which makes non-semantic content irrelevant.
To illustrate, the implementation of XNode.DeepEquals returns false for these semantically-equivalent documents:
XElement root1 = XElement.Parse("<Root a='1' b='2'><Child>1</Child></Root>");
XElement root2 = XElement.Parse("<Root b='2' a='1'><Child>1</Child></Root>");
However, using the implementation of DeepEqualsWithNormalization from the article, you'll get the value true because the ordering of attributes is not considered significant. This implementation is included below.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;
using System.Xml.Schema;
public static class MyExtensions
{
public static string ToStringAlignAttributes(this XDocument document)
{
XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;
settings.OmitXmlDeclaration = true;
settings.NewLineOnAttributes = true;
StringBuilder stringBuilder = new StringBuilder();
using (XmlWriter xmlWriter = XmlWriter.Create(stringBuilder, settings))
document.WriteTo(xmlWriter);
return stringBuilder.ToString();
}
}
class Program
{
private static class Xsi
{
public static XNamespace xsi = "http://www.w3.org/2001/XMLSchema-instance";
public static XName schemaLocation = xsi + "schemaLocation";
public static XName noNamespaceSchemaLocation = xsi + "noNamespaceSchemaLocation";
}
public static XDocument Normalize(XDocument source, XmlSchemaSet schema)
{
bool havePSVI = false;
// validate, throw errors, add PSVI information
if (schema != null)
{
source.Validate(schema, null, true);
havePSVI = true;
}
return new XDocument(
source.Declaration,
source.Nodes().Select(n =>
{
// Remove comments, processing instructions, and text nodes that are
// children of XDocument. Only white space text nodes are allowed as
// children of a document, so we can remove all text nodes.
if (n is XComment || n is XProcessingInstruction || n is XText)
return null;
XElement e = n as XElement;
if (e != null)
return NormalizeElement(e, havePSVI);
return n;
}
)
);
}
public static bool DeepEqualsWithNormalization(XDocument doc1, XDocument doc2,
XmlSchemaSet schemaSet)
{
XDocument d1 = Normalize(doc1, schemaSet);
XDocument d2 = Normalize(doc2, schemaSet);
return XNode.DeepEquals(d1, d2);
}
private static IEnumerable<XAttribute> NormalizeAttributes(XElement element,
bool havePSVI)
{
return element.Attributes()
.Where(a => !a.IsNamespaceDeclaration &&
a.Name != Xsi.schemaLocation &&
a.Name != Xsi.noNamespaceSchemaLocation)
.OrderBy(a => a.Name.NamespaceName)
.ThenBy(a => a.Name.LocalName)
.Select(
a =>
{
if (havePSVI)
{
var dt = a.GetSchemaInfo().SchemaType.TypeCode;
switch (dt)
{
case XmlTypeCode.Boolean:
return new XAttribute(a.Name, (bool)a);
case XmlTypeCode.DateTime:
return new XAttribute(a.Name, (DateTime)a);
case XmlTypeCode.Decimal:
return new XAttribute(a.Name, (decimal)a);
case XmlTypeCode.Double:
return new XAttribute(a.Name, (double)a);
case XmlTypeCode.Float:
return new XAttribute(a.Name, (float)a);
case XmlTypeCode.HexBinary:
case XmlTypeCode.Language:
return new XAttribute(a.Name,
((string)a).ToLower());
}
}
return a;
}
);
}
private static XNode NormalizeNode(XNode node, bool havePSVI)
{
// trim comments and processing instructions from normalized tree
if (node is XComment || node is XProcessingInstruction)
return null;
XElement e = node as XElement;
if (e != null)
return NormalizeElement(e, havePSVI);
// Only thing left is XCData and XText, so clone them
return node;
}
private static XElement NormalizeElement(XElement element, bool havePSVI)
{
if (havePSVI)
{
var dt = element.GetSchemaInfo();
switch (dt.SchemaType.TypeCode)
{
case XmlTypeCode.Boolean:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
(bool)element);
case XmlTypeCode.DateTime:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
(DateTime)element);
case XmlTypeCode.Decimal:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
(decimal)element);
case XmlTypeCode.Double:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
(double)element);
case XmlTypeCode.Float:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
(float)element);
case XmlTypeCode.HexBinary:
case XmlTypeCode.Language:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
((string)element).ToLower());
default:
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
element.Nodes().Select(n => NormalizeNode(n, havePSVI))
);
}
}
else
{
return new XElement(element.Name,
NormalizeAttributes(element, havePSVI),
element.Nodes().Select(n => NormalizeNode(n, havePSVI))
);
}
}
}
I started down the same path as @llasarov, but also didn't like the use of strings either. I discovered XElement.DeepEquals() here, so finding the question helped me.
I could see that it could be difficult if your test returns a massive XML structure, but in my opinion, this should not be done - the test should check as small a structure as possible.
Say you have a method that you expect to return an element that looks like <Test Sample="Value" />. You can use the XElement and XAttribute constructors to build your expected value pretty easily, like this:
[TestMethod()]
public void MyXmlMethodTest()
{
// Use XElement API to build expected element.
XElement expected = new XElement("Test", new XAttribute("Sample", "Value"));
// Call the method being tested.
XElement actual = MyXmlMethod();
// Assert using XNode.DeepEquals
Assert.IsTrue(XNode.DeepEquals(expected, actual));
}
Even if there are a handful of elements and attributes, this is manageable and consistent.