How to merge two XmlDocuments in C#

Question

I want to merge two XmlDocuments by inserting a second XML doc to the end of an existing Xmldocument in C#. How is this done?

Answer 1

Bad news. As long as the xml documents can have only one root element you cannot just put content of one document at the end of the second. Maybe this is what you are looking for? It shows how easily you can merge xml files using Linq-to-XML

Alternatively if you are using XmlDocuments you can try make it like this:

XmlDocument documentA;
XmlDocument documentB;

foreach(var childNode in documentA.DocumentElement.ChildNodes)
   documentB.DocumentElement.AppendChild(childNode);

Answer 2

Something like this:

foreach (XmlNode node in documentB.DocumentElement.ChildNodes)
{
    XmlNode imported = documentA.ImportNode(node, true);
    documentA.DocumentElement.AppendChild(imported);
}

Note that this ignores the document element itself of document B - so if that has a different element name, or attributes you want to copy over, you'll need to work out exactly what you want to do.

EDIT: If, as per your comment, you want to embed the whole of document B within document A, that's relatively easy:

XmlNode importedDocument = documentA.ImportNode(documentB.DocumentElement, true);
documentA.DocumentElement.AppendChild(importedDocument);

This will still ignore things like the XML declaration of document B if there is one - I don't know what would happen if you tried to import the document itself as a node of a different document, and it included an XML declaration... but I suspect this will do what you want.

Answer 3

Inserting an entire XML document at the end of another XML document is actually guaranteed to produce invalid XML. XML requires that there be one, and only one "document" element. So, assuming that your files were as follows:

A.xml

<document>
   <element>value1</element>
   <element>value2</element>
</document>

B.xml

<document>
   <element>value3</element>
   <element>value4</element>
</document>

The resultant document by just appending one at the end of the other:

<document>
   <element>value1</element>
   <element>value2</element>
</document>
<document>
   <element>value3</element>
   <element>value4</element>
</document>

Is invalid XML.

Assuming, instead, that the two documents share a common document element, and you want to insert the children of the document element from B into A's document element, you could use the following:

var docA = new XmlDocument();
var docB = new XmlDocument();

foreach (var childEl in docB.DocumentElement.ChildNodes) {
    var newNode = docA.ImportNode(childEl, true);
    docA.DocumentElement.AppendChild(newNode);
}

This will produce the following document given my examples above:

<document>
   <element>value1</element>
   <element>value2</element>
   <element>value3</element>
   <element>value4</element>
</document>