How would you compare two XML Documents?

StackOverflow https://stackoverflow.com/questions/167946

Question

As part of the base class for some extensive unit testing, I am writing a helper function which recursively compares the nodes of one XmlDocument object to another in C# (.NET). Some requirements of this:

  • The first document is the source, e.g. what I want the XML document to look like. Thus the second is the one I want to find differences in and it must not contain extra nodes not in the first document.
  • Must throw an exception when too many significant differences are found, and it should be easily understood by a human glancing at the description.
  • Child element order is important, attributes can be in any order.
  • Some attributes are ignorable; specifically xsi:schemaLocation and xmlns:xsi, though I would like to be able to pass in which ones are.
  • Prefixes for namespaces must match in both attributes and elements.
  • Whitespace between elements is irrelevant.
  • Elements will either have child elements or InnerText, but not both.

While I'm scrapping something together: has anyone written such code and would it be possible to share it here?

On an aside, what would you call the first and second documents? I've been referring to them as "source" and "target", but it feels wrong since the source is what I want the target to look like, else I throw an exception.

Was it helpful?

Solution

Microsoft has an XML diff API that you can use

OTHER TIPS

try XMLUnit. This library is available for both Java and .Net

Comparing XML documents is complicated. Google for xmldiff (there's even a Microsoft solution) for some tools. I've solved this a couple of ways. I used XSLT to sort elements and attributes (because sometimes they would appear in a different order, and I didn't care about that), and filter out attributes I didn't want to compare, and then either used the XML::Diff or XML::SemanticDiff perl module, or pretty printed each document with every element and attribute on a separate line, and using Unix command line diff on the results.

This code doesn't satisfy all your requirements, but it's simple and I'm using for my unit tests. Attribute order doesn't matter, but element order does. Element inner text is not compared. I also ignored case when comparing attributes, but you can easily remove that.

public bool XMLCompare(XElement primary, XElement secondary)
{
    if (primary.HasAttributes) {
        if (primary.Attributes().Count() != secondary.Attributes().Count())
            return false;
        foreach (XAttribute attr in primary.Attributes()) {
            if (secondary.Attribute(attr.Name.LocalName) == null)
                return false;
            if (attr.Value.ToLower() != secondary.Attribute(attr.Name.LocalName).Value.ToLower())
                return false;
        }
    }
    if (primary.HasElements) {
        if (primary.Elements().Count() != secondary.Elements().Count())
            return false;
        for (var i = 0; i <= primary.Elements().Count() - 1; i++) {
            if (XMLCompare(primary.Elements().Skip(i).Take(1).Single(), secondary.Elements().Skip(i).Take(1).Single()) == false)
                return false;
        }
    }
    return true;
}

I am using ExamXML for comparing XML files. You can try it. The authors, A7Soft, also provide API for comparing XML files

https://github.com/CameronWills/FatAntelope Another alternative library to the Microsoft XML Diff API. It has a XML diffing algorithm to do an unordered comparison of two XML documents and produce an optimal matching.

It is a C# port of the X-Diff algorithm described here: http://pages.cs.wisc.edu/~yuanwang/xdiff.html

Disclaimer: I wrote it :)

Another way to do this would be -

  1. Get the contents of both files into two different strings.
  2. Transform the strings using an XSLT (which will just copy everything over to two new strings). This will ensure that all spaces outside the elements are removed. This will result it two new strings.
  3. Now, just compare the two strings with each other.

This won't give you the exact location of the difference, but if you just want to know if there is a difference, this is easy to do without any third party libraries.

Not relevant for the OP since it currently ignores child order, but if you want a code only solution you can try XmlSpecificationCompare which I somewhat misguidedly developed.

For comparing two XML outputs in automated testing I found XNode.DeepEquals.

Compares the values of two nodes, including the values of all descendant nodes.

Usage:

var xDoc1 = XDocument.Parse(xmlString1);
var xDoc2 = XDocument.Parse(xmlString2);

bool isSame = XNode.DeepEquals(xDoc1.Document, xDoc2.Document);
//Assert.IsTrue(isSame);

Reference: https://docs.microsoft.com/en-us/dotnet/api/system.xml.linq.xnode.deepequals?view=netcore-2.2

Based @Two Cents answer and using this link XMLSorting i have created my own XmlComparer

Compare XML program

private static bool compareXML(XmlNode node, XmlNode comparenode)
    {

        if (node.Value != comparenode.Value)
            return false;

            if (node.Attributes.Count>0)
            {
                foreach (XmlAttribute parentnodeattribute in node.Attributes)
                {
                    string parentattributename = parentnodeattribute.Name;
                    string parentattributevalue = parentnodeattribute.Value;
                    if (parentattributevalue != comparenode.Attributes[parentattributename].Value)
                    {
                        return false;
                    }

                }

            }

          if(node.HasChildNodes)
            {
            sortXML(comparenode);
            if (node.ChildNodes.Count != comparenode.ChildNodes.Count)
                return false;
            for(int i=0; i<node.ChildNodes.Count;i++)
                {

                string name = node.ChildNodes[i].LocalName;
                if (compareXML(node.ChildNodes[i], comparenode.ChildNodes[i]) == false)
                    return false;
                }

            }



        return true;
    }

Sort XML program

 private static void sortXML(XmlNode documentElement)
    {
        int i = 1;
        SortAttributes(documentElement.Attributes);
        SortElements(documentElement);
        foreach (XmlNode childNode in documentElement.ChildNodes)
        {
            sortXML(childNode);

        }
    }



  private static void SortElements(XmlNode rootNode)
    {



            for(int j = 0; j < rootNode.ChildNodes.Count; j++) {
                for (int i = 1; i < rootNode.ChildNodes.Count; i++)
                {
                    if (String.Compare(rootNode.ChildNodes[i].Name, rootNode.ChildNodes[1 - 1].Name) < 0)
                    {
                        rootNode.InsertBefore(rootNode.ChildNodes[i], rootNode.ChildNodes[i - 1]);

                    }


                }
            }
           // Console.WriteLine(j++);


    }
 private static void SortAttributes(XmlAttributeCollection attribCol)
    {
        if (attribCol == null)
            return;
        bool changed = true;
        while (changed)
        {
            changed = false;
            for (int i = 1; i < attribCol.Count; i++)
        {
                if (String.Compare(attribCol[i].Name, attribCol[i - 1].Name) < 0)
                {
                    //Replace
                    attribCol.InsertBefore(attribCol[i], attribCol[i - 1]);
                    changed = true;

                }
            }
        }
    }

I wrote this XSLT 1.0 based comparison sheet that you compare b.xml to the input xml outputting differences of items in the input that are not in b.xml.

https://github.com/sflynn1812/xslt-diff

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