Oh, yes. Thank you Martin.
That is obviously a good point.
The input is a database with several thousands of documents stored in it.
The filters are a dynamic sequence of xpath expressions to be applied on
the documents expressed as function references.
I need to check whether I can compress all this into a simple predicate
as you've shown in your example.
where clause would have been much more easier in conjunction with the
map operator (!) but if it works I'm going to coope with the predicate.
Thanks for your suggestion in the meanwhile.
Here a simplified example of my current approach where you could think
of /$filters/ as a sequence of boolean functions to be applied to the
documents in the db.
let $seq :=
for $doc in db:open("adatabase")
where not(false() = ($filters ! (.($doc)))
return $doc
let $out :=
for tumbling window $w in $seq
start $first at $s when ($s = 1 + ($page - 1) * $count)
end $last at $e when $e - $s = $count - 1
return $w
Regards,
Marco.
On 28/08/2018 14:19, Martin Honnen wrote:
On 28.08.2018 11:04, Marco Lettere wrote:
here's a question related to XQuery, sorry for being slightly off-topic.
I'm struggling to find a way to combine the windowing clause and
FLOWR in order to get a paged result of a subset of items which
respect a given filter.
Of course I'm able to get this by first applying the filter to the
whole input and then a second FLOWR for the windowing clause.
So what is the filter condition? What is the input sequence?
The closer I get is [1] which is not what I'd need because I get
2,4,6,8,10 as result for page 1 but I'd really want 10 results per
page thus 2,4,6,8,10,12,14,16,18,20.
Thanks for any help on this in the meanwhile I'll stick to my naive
solution.
Marco.
[1]
let $page := 1
let $count := 10
return
for tumbling window $w in (1 to 100)
start $first at $s when ($s = 1 + ($page - 1) * $count)
end $last at $e when ($e - $s = $count - 1)
return
$w ! (if (. mod 2 = 0 ) then . else ())
Can't you simply use the filter as a predicate on the expression you
use in the windowing for clause?
Does
let $page-size := 10
for tumbling window $page in (1 to 100)[. mod 2 = 0]
start at $sp when $sp mod $page-size = 1
end at $np when ($np + 1) mod $page-size = 1
return <page>{$page}</page>
help?
It returns
<page>2 4 6 8 10 12 14 16 18 20</page>
<page>22 24 26 28 30 32 34 36 38 40</page>
<page>42 44 46 48 50 52 54 56 58 60</page>
<page>62 64 66 68 70 72 74 76 78 80</page>
<page>82 84 86 88 90 92 94 96 98 100</page>
