Question

I’m failing in my first attempt to get the fn:id() XQuery function to do something.

So far I have a document called bar.xml;

<bar>
    <foo id="a"/>
    <foo id="b"/>
    <foo id="c"/>
</bar>

And an XQuery;

doc('bar.xml')/fn:id(("a", "c"))

But everything I try just seems to return an empty set.

I have yet to learn XML schemas. Can fn:id() work without declaring a separate schema file for bar.xml?

Answer 1

You need to indicate that your id attributes are ids.

One way to do this is to add a schema or DTD to the document that specifies this.

The other (far easier) way is to use xml:id in place of id in your document.

On a related note, you may wish to use element-with-id() instead of id(). element-with-id() does what id() was originally intended to do, and id remains in the specification for compatibility reasons.