Question

I have an application which extracts data from an XML file using XPath. If a node in that XML source file is missing I want to return the value ‘N/A’ (much like the Oracle NVL function). The trick is that the application doesn’t support XSLT; I’d like to do this using XPath and XPath alone.

Is that possible?

Answer 1

It can be done but only if the return value when the node does exist is the string value of the node, not the node itself. The XPath

substring(concat('N/A', /foo/baz), 4 * number(boolean(/foo/baz))) 

will return the string value of the baz element if it exists, otherwise the string ‘N/A’.

To generalize the approach:

substring(concat($null-value, $node),           (string-length($null-value) + 1) * number(boolean($node))) 

where $null-value is the null value string and $node the expression to select the node. Note that if $node evaluates to a node-set that contains more than one node, the string value of the first node is used.