Getting A ColdFusion XML Document Reference From An XML Node In Order To Create A New XML Element

This weekend, I was experimenting with some sexy ColdFusion XML manipulation when I ran into a bit of a problem. I found myself in a situation in which I needed to create a new XML element based on an existing XML element. The problem with doing this is that in order to create a new XML element in ColdFusion, you need a reference to the XML document in which the new element will be created (XML elements are "owned" by an XML document). So, if you only have an existing XML element, you need to finagle your way back up to the original XML document reference.

In ColdFusion, XML can be a bit confusing because there is a subtle yet very important difference between a ColdFusion XML document and the XML data that it contains. This difference is made even less obvious when you consider that xmlSearch() can be used to search both XML documents and XML nodes. Most of the time, this difference doesn't matter to us; but, when we need to create a new XML element, understanding this difference is critical. To see why, take a look at the following code:

In this demo, we have a ColdFusion XML document referenced in the variable, girls. When then try to create two new XML elements for said XML document using xmlElemNew(). One call to xmlElemNew() uses the girls variable while the other uses the root XML element. When we run this code, we get the following output:

isHotNode Exists: YES

isCuteNode Exists: NO

As you can see, when using the XML document reference, xmlElemNew() was able to create and return a new XML element. When using an XML element, on the other hand, xmlElemNew() returned null. In other words, ColdFusion could not create a new XML element based on another XML element.

I think this is a significant shortcoming of the xmlElemNew() function; but, we can get around it. Look at how we got the root XML element in the above demo:

The XML element that we used in the latter part of our demo - the root XML element - is a child of the XML document. This then begs the question - is the ColdFusion XML document a parent of the root XML element? To test this, we can rerun the above code using an xmlParent reference:

This time, when creating the isCuteNode XML element, we dip down into the root XML element but then try to climb our way back up to the XML document using xmlParent:

When we run this code, we get the following output:

isHotNode Exists: YES

isCuteNode Exists: YES

Woohoo! ColdFusion was able to create both XML elements. This tells us that the XML document reference required by the xmlElemNew() function can be obtained from the root XML element.

In the preceding example, it was easy to get the XML document reference because we started with the root XML node; but, what if we don't have the root XML node? What if we have some deeply nested XML element? This was exactly the situation I found myself in over the weekend - I had to create a new XML element based on some arbitrary existing XML node reference.

In that kind of a situation, a single call to xmlParent probably won't do the trick (unless you have the root XML element). As such, we need a way to get to the root XLM element such that we can get to the parent XML document. Luckily, xmlSearch() allows us to do just that. By using the XPath query, "/*", we can select the root XML element from any XML node starting point:

This demo uses two approaches for obtaining the XML document reference. Both use xmlSearch(); but, each gets the XML document reference in a slightly different way. The first uses the ".." path traversal directive to jump from the root XML element to the XML document reference; the second uses only the "/*" traversal directive and then uses the xmlParent property to get the XML document reference (much like our second demo). When we run this code, we can see that both approaches work:

xmlDocNodes: YES

xmlRootNodes: YES

We now know that we can get the XML document reference based on any XML element; but, this is kind of sloppy. As a last step in our exploration, let's encapsulate this logic in a nice ColdFusion user defined function (UDF), xmlGetDoc():

Notice in this demo that we are testing our xmlGetDoc() UDF with both an XML element reference and an XML document reference. Since xmlSearch() works with both types of values, our xmlGetDoc() UDF does not need to care about the subtle differences between XML documents and XML nodes. When we run the above code, we get the following output:

isXmlDoc: YES

isXmlDoc: YES

As you can see, we were able to obtain the XML document reference from both an existing XML node and an existing XML document value.

To me, it seems like a shortcoming that the xmlElemNew() function cannot create a new XML element based on any existing XML node reference. Since XML nodes can be searched, aggregated, and passed by reference, it would make more sense for the xmlElemNew() function to be more flexible. However, until the behavior of xmlElemNew() changes, at least we can manually locate the parent XML document.

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