XQuery wrap result in computed node - xquery

Question

I am trying to do some simple pagination in XQuery. I would like my root element of the returned XML to have (as attributes) various properties about the pagination (current page etc).
However I can't seem to find a way to add these dynamic attributes to my root element.
I've tried playing with the
element name {expr} and attribute name {expr}
functions, but can't seem to get them to work.
<result>{
let $results :=
for $item in doc('mydoc')/root/item
return $item
let $requested-page-nbr := 2
let $items-per-page := 10
let $count := count($results)
let $last-page-nbr := fn:ceiling($count div $items-per-page)
let $actual-page-nbr := if ($requested-page-nbr gt $last-page-nbr) then $last-page-nbr else $requested-page-nbr
let $start-item := $items-per-page * $actual-page-nbr - ( $items-per-page - 1 )
let $natural-end-item := $actual-page-nbr * $items-per-page
let $actual-end-item := if ($count ge $natural-end-item) then $natural-end-item else $count
for $j in ($start-item to $actual-end-item )
let $current := item-at($results, $j)
return
<document-summary
requested-page-nbr="{$requested-page-nbr}"
items-per-page="{$items-per-page}"
count="{$count}"
last-page-nbr="{$last-page-nbr}"
actual-page-nbr="{$actual-page-nbr}"
start-item="{$start-item}"
natural-end-item="{$natural-end-item}"
actual-end-item="{$actual-end-item}">
{($current)}
</document-summary>
}</result>

Answer 1

to add an attribute to the root:
<result>{attribute page {3}}</result>
in your case you probably want to do something like: (?)
...
return (
attribute page {$actual-page-nbr},
for $j in ($start-item to $actual-end-item )
let $current := item-at($results, $j)
return
<document-summary
requested-page-nbr="{$requested-page-nbr}"
items-per-page="{$items-per-page}"
count="{$count}"
last-page-nbr="{$last-page-nbr}"
actual-page-nbr="{$actual-page-nbr}"
start-item="{$start-item}"
natural-end-item="{$natural-end-item}"
actual-end-item="{$actual-end-item}">
{($current)}
</document-summary>)
...
does that answer your question?

Answer 2

I don't think that is the proper XQuery way...
This XQuery:
declare variable $requested-page-nbr external;
declare variable $items-per-page external;
declare variable $items := /root/item;
declare variable $firsties := $items[position() mod $items-per-page = 1];
for $first in $firsties
let $actual-page-nbr := index-of($firsties,$first)
let $group := $first|
$first/following-sibling::item[position() < $items-per-page]
let $previous := ($actual-page-nbr - 1) * $items-per-page
where $actual-page-nbr = $requested-page-nbr
return
<result>
<document-summary requested-page-nbr="{$requested-page-nbr}"
items-per-page="{$items-per-page}"
count="{count($items)}"
last-page-nbr="{count($firsties)}"
actual-page-nbr="{$actual-page-nbr}"
start-item="{$previous + 1}"
natural-end-item="{$previous + $items-per-page}"
actual-end-item="{$previous + count($group)}">{
$group
}</document-summary>
</result>
With this input:
<root>
<item>1</item>
<item>2</item>
<item>3</item>
<item>4</item>
<item>5</item>
<item>6</item>
<item>7</item>
<item>8</item>
<item>9</item>
<item>10</item>
<item>11</item>
<item>12</item>
<item>13</item>
</root>
With $requested-page-nbr set to 2 and $items-per-page set to 3, output:
<result>
<document-summary requested-page-nbr="2"
items-per-page="3"
count="13"
last-page-nbr="5"
actual-page-nbr="2"
start-item="4"
natural-end-item="6"
actual-end-item="6">
<item>4</item>
<item>5</item>
<item>6</item>
</document-summary>
</result>
With $requested-page-nbr set to 4 and $items-per-page set to 4, output:
<result>
<document-summary requested-page-nbr="4"
items-per-page="4"
count="13"
last-page-nbr="4"
actual-page-nbr="4"
start-item="13"
natural-end-item="16"
actual-end-item="13">
<item>13</item>
</document-summary>
</result>

Answer 3

As for returning a "page" of results, where you are using
{($current)}
we are using something like the following
{ subsequence($results, $start-item, $items-per-page) }