Xml – Merge XML documents

xml

I need to "merge" two XML documents, overwriting the overlapsed attributes and elements. For instance if I have document1:

<mapping>
    <key value="assigned">
        <a/>
    </key>
    <whatever attribute="x">
        <k/>
        <j/>
    </whatever>
</mapping>

and document2:

<mapping>
    <key value="identity">
        <a/>
        <b/>
    </key>
</mapping>

I want to merge the two like this:

<mapping>
    <key value="identity">
        <a/>
        <b/>
    </key>
    <whatever attribute="x">
        <k/>
        <j/>
    </whatever>
</mapping>

I prefer Java or XSLT-based solutions, ant will do fine, but if there's an easy way to do that in Rake, Ruby or Python please don't be shy 🙂

EDIT: actually I find I'd rather use an automated tool/script, even writing it by myself, because manually merging some 30 XML files is a bit unwieldy… 🙁

Best Solution

If you like XSLT, there's a nice merge script I've used before at: Oliver's XSLT page

XML escape characters

There are only five:

"   &quot;
'   &apos;
<   &lt;
>   &gt;
&   &amp;

Escaping characters depends on where the special character is used.

The examples can be validated at the W3C Markup Validation Service.

Text

The safe way is to escape all five characters in text. However, the three characters ", ' and > needn't be escaped in text:

<?xml version="1.0"?>
<valid>"'></valid>

Attributes

The safe way is to escape all five characters in attributes. However, the > character needn't be escaped in attributes:

<?xml version="1.0"?>
<valid attribute=">"/>

The ' character needn't be escaped in attributes if the quotes are ":

<?xml version="1.0"?>
<valid attribute="'"/>

Likewise, the " needn't be escaped in attributes if the quotes are ':

<?xml version="1.0"?>
<valid attribute='"'/>

Comments

All five special characters must not be escaped in comments:

<?xml version="1.0"?>
<valid>
<!-- "'<>& -->
</valid>

CDATA

All five special characters must not be escaped in CDATA sections:

<?xml version="1.0"?>
<valid>
<![CDATA["'<>&]]>
</valid>

Processing instructions

All five special characters must not be escaped in XML processing instructions:

<?xml version="1.0"?>
<?process <"'&> ?>
<valid/>

XML vs. HTML

HTML has its own set of escape codes which cover a lot more characters.

C# – Loose merge of XML documents

Sounds like a job for LINQ to XML!

var vidDoc = XDocument.Parse(vidXml);
var rssDoc = XDocument.Parse(rssXml);
var videos = vidDoc.XPathSelectElements("/videos/video");
var rssItems = rssDoc.XPathSelectElements("/rss/channel/item");
var matches = videos.Join(
    rssItems,
    video => video.Element(XName.Get("code")).Value,
    rssItem => rssItem.Element(XName.Get("code", "http://test.com")).Value,
    (video, item) => new {video, item});

foreach (var match in matches)
{
    var children = match.item.Elements()
        .Where(child => child.Name.NamespaceName == "http://test.com" &&
                        child.Name.LocalName != "code");

    foreach (var child in children)
    {
        //remove the namespace
        child.Name = XName.Get(child.Name.LocalName);
        match.video.Add(child);
    }
}

vidDoc.Save(Console.Out);

The above solution assumes that the RSS document looks something like this:

<rss xmlns:ns="http://test.com" version="2.0">
  <channel>
    <item>
      <title>AAA123</title>
      <link>http://test.com/AAA123</link>
      <pubDate>Sun, 26 Jul 2009 23:59:59 -0800</pubDate>
      <ns:code>AAA123</ns:code>
      <ns:type>Awesome</ns:type>
      <ns:group>Wonderful</ns:group>
    </item>
  </channel>
</rss>