Help Merging XML Data

Question

I have two XMLDocuments that contain some similar information but there are other nodes that contain different information between the two.

I am using XMLSerialization to put my data into a structure as shown here

I know you can merge XML files by using a DataSet as shown here but I want to somehow serialize the first document I see into my class and then append the second document to my class structure.

Any ideas how to do that or is there a better approach? On the second document where the information is similar I am happy to overwrite it with the second document data for example each document has a DATE so my Date property can be that of the second document.

Here is the data

<ROOT>
<ID>2</ID>
<PART>4a</PART>
<NAME>JEFF</NAME>
<ADDRESS>
    <ST>10001</ST>
    <ID>123456789</ID>
</ADDRESS>
<PARTNUMBER>001</PARTNUMBER>
<DATE>2009 -06-05T16.18.05</DATE>
</ROOT>


<ROOT>
<ID>2</ID>
<PART>4b</PART>
<NAME>JEFF</NAME>
<RELATIVE>
    <ST>10001</ST>
    <ID>1234567890QWERTYUIOP</ID>
</RELATIVE>
<PARTNUMBER>002</PARTNUMBER>
<DATE>2009 -06-05T16.17.41</DATE>
</ROOT>

Answer 1

Thomas' answer is really great. However although it worked perfectly well on the given XML, I found it had some trouble on XML with attributes (although the code does theoretically deal with it).

However this line would throw an InvalidCastException trying to convert from XAttribute to XNode:

var nodes = attributes.Concat(elements).ToArray();

Nonetheless I found that the following changes worked for me. Instead of

var attributes = e2.Attributes().Union(e1.Attributes(), attrComparer).Cast<XNode>();
...
var nodes = attributes.Concat(elements).ToArray();
...
if (value != null)
    return new XElement(e1.Name, nodes, value);
else
    return new XElement(e1.Name, nodes);

Try this:

var attributes = e2.Attributes().Union(e1.Attributes(), attrComparer);
...
// var nodes = attributes.Concat(elements).ToArray();
...
if (value != null)
    return new XElement(e1.Name, attributes, elements, value);
else
    return new XElement(e1.Name, attributes, elements);

Seems to work for me, though I'm no expert on these matters. This is just an FYI for anyone else who comes across this.

EDIT: In addition, note that doc.Dump() doesn't exist for me and breaks when compiling. I'm using .NET 3.5; perhaps Tom's answer depended on a different version (3.0?), and that might also account for the error messages I got?

Answer 2

You can do something like that :

void Main()
{
    string xml1 = @"<ROOT>
    <ID>2</ID>
    <PART>4a</PART>
    <NAME>JEFF</NAME>
    <ADDRESS>
        <ST>10001</ST>
        <ID>123456789</ID>
    </ADDRESS>
    <PARTNUMBER>001</PARTNUMBER>
    <DATE>2009 -06-05T16.18.05</DATE>
    </ROOT>";


    string xml2 = @"<ROOT>
    <ID>2</ID>
    <PART>4b</PART>
    <NAME>JEFF</NAME>
    <RELATIVE>
        <ST>10001</ST>
        <ID>1234567890QWERTYUIOP</ID>
    </RELATIVE>
    <PARTNUMBER>002</PARTNUMBER>
    <DATE>2009 -06-05T16.17.41</DATE>
    </ROOT>";

    var doc1 = XDocument.Parse(xml1);
    var doc2 = XDocument.Parse(xml2);

    XDocument doc = MergeDocuments(doc1, doc2);
    doc.Dump();
}

static XDocument MergeDocuments(XDocument doc1, XDocument doc2)
{
    var root = MergeElements(doc1.Root, doc2.Root);
    return new XDocument(root);
}

static XElement MergeElements(XElement e1, XElement e2)
{
    var attrComparer = new XAttributeEqualityComparer();
    var nameComparer = new XNameComparer();

    var attributes = e2.Attributes().Union(e1.Attributes(), attrComparer).Cast<XNode>();

    var elements1 = e1.Elements().OrderBy(e => e.Name, nameComparer).ToArray();
    var elements2 = e2.Elements().OrderBy(e => e.Name, nameComparer).ToArray();
    var elements = new List<XNode>();
    int i1 = 0, i2 = 0;
    while (i1 < elements1.Length && i2 < elements2.Length)
    {
        XElement e = null;
        int compResult = nameComparer.Compare(elements1[i1].Name, elements2[i2].Name);
        if (compResult < 0)
        {
            e = elements1[i1];
            i1++;
        }
        else if (compResult > 0)
        {
            e = elements2[i2];
            i2++;
        }
        else
        {
            e = MergeElements(elements1[i1], elements2[i2]);
            i1++;
            i2++;
        }
        elements.Add(e);
    }
    while (i1 < elements1.Length)
    {
        elements.Add(elements1[i1]);
        i1++;
    }
    while (i2 < elements2.Length)
    {
        elements.Add(elements2[i2]);
        i2++;
    }

    var nodes = attributes.Concat(elements).ToArray();
    string value = null;
    if (elements.Count == 0)
    {
        if (!string.IsNullOrEmpty(e1.Value))
            value = e1.Value;
        if (!string.IsNullOrEmpty(e2.Value))
            value = e2.Value;
    }
    if (value != null)
        return new XElement(e1.Name, nodes, value);
    else
        return new XElement(e1.Name, nodes);
}

class XNameComparer : IComparer<XName>
{
    public int Compare(XName x, XName y)
    {
        int result = string.Compare(x.Namespace.NamespaceName, y.Namespace.NamespaceName);
        if (result == 0)
            result = string.Compare(x.LocalName, y.LocalName);
        return result;
    }
}

class XAttributeEqualityComparer : IEqualityComparer<XAttribute>
{
    public bool Equals(XAttribute x, XAttribute y)
    {
        return x.Name == y.Name;
    }

    public int GetHashCode(XAttribute x)
    {
        return x.Name.GetHashCode();
    }
}