关于项目的XQuery

Question

I know how to use the For instruction to create a loop on a collection or on a document but I have troubles to create a loop on an item()*

content of item()*:

<Placemark>
    <blabla id="1">
        <value>abcd</value>
    </blabla>
    <blabla id="2">
        <value>abcd</value>
    </blabla>
    ...
</Placemark>
<Placemark>
    ...
</Placemark>

Now I need for example the <blabla> elements only. With a classic loop on a document, I access like this :

for $x in doc("/db/data.xml")/Placemark
return $x

but with a loop on a item()*, it doesn't work like this :

declare function local:fct($content as item()*) as item()* {
    for $x in $content/Placemark
    return $x
};

I have no error, just a blank result. Someone know why it doesn't work?

Answer 1

Because your loop is already iterating over Placemark items, your solution asks for Placemark children of Placemark , which is empty.

declare function local:fct(
  $content as element(Placemark)*
) as element(blabla)* {
    for $x in $content
    return $x/blabla
};

Answer 2

If you were passing the parent of the Placemark elements to the function as the value of the $content parameter, your code would be fine. But it looks as if you're calling the function with some expression like local:fct(doc(...)//Placemark) , which means the members of the $content sequence are themselves the Placemark elements. Your function then asks for their Placemark children; there are none, so the empty sequence is what you get.

The revised function suggested by wst is a fine way to fix the problem; passing in the parents of the Placemark elements as the value of $content would be another fine way.