xquery parameter query

Question

I'm trying to query an exist-db with xquery by taking parameters from the URL and building up seach parameters

xquery version "1.0";
declare namespace request="http://exist-db.org/xquery/request";
declare namespace xs="http://www.w3.org/2001/XMLSchema";
declare option exist:serialize "method=xml media-type=text/xml omit-xml-declaration=no indent=yes";

let $param1:= request:get-parameter("param1",'0')

let $person :=
    if($param1 = '0') 
    then "'*'"
    else concat('contributions/person/@val="',$param1,'"')

return

<xml>
{
    for $x in subsequence(//foo/bar[$person],1,3)
    return $x
}
</xml>

The code above shows that I get the parameter from the url $param1.

variable $person checks to see if there was a parameter and based on that creates a query parameter. This variable works fine, from testing it prints out either '*' for no param or

contributions/person/@val='hello, world'

When I run the query it prints out as if the value is '*'. In the for $x part, can I pass a variable like that? I've tried putting concat($person,'') with the same results. Hardcoding the full path gives me the results I'm looking for, but I'm looking to create something more dynamic.

To note: there is only one variable, $person, but there will be others once I get it to work

I think the problem is that $person is now a string and now a path. But I can't seem to not keep it as a string. — user9418
– user9418, Commented Oct 22, 2012 at 15:14

wst · Accepted Answer · 2012-10-22 15:17:37Z

1

I think ideally you would avoid dynamic string evaluation. In this example, some pretty simple reorganization would solve the problem without it:

<xml>
{
  for $x in subsequence(//foo/bar[
    if ($param1 = '0')
    then *
    else (contributions/person/@val = $param1)
  ],1,3)
  return $x
}
</xml>

However, you can use eval(), but keep in mind there are security risks:

<xml>
{
  for $x in subsequence(eval(
    concat('//foo/bar[',$person,']')
  ),1,3)
  return $x
}
</xml>

answered Oct 22, 2012 at 15:17

wst

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5 Comments

user9418 Over a year ago

May have spoken too soon. If I wanted to check $param2 with the same expression but contribution/link/@val = 'test'. How would I do that? I did 'and if($param2 = "0")' but I get this error message :- error FORG0006: effectiveBooleanValue: first item of '(false, false)' is not a node, and sequence length > 1

wst Over a year ago

@user9418 If I understand you correctly, I think you just need if (($param1 = '0') and ($param2 = '0'))

user9418 Over a year ago

What I'm trying to achieve is more of a faceted search like pastebin.com/CYAdpUi5 but based off of your example I'm getting an error message in oxygen on the first then. When I run the query I get 'Parse error: element name containing whitespace: unexpected token: then at line: 15 column: 25'

user9418 Over a year ago

OK, managed to get it to work pastebin.com/8jTcWjuy - performance is a bit slow. But thanks for your help

Joe Wicentowski Over a year ago

Probably not the most efficient code (referring to your pastebin link that you just said works). For example, the for loop is unnecessary - just directly call the subsequence function instead of iterating over its results just to return them all. Also, you test for whether ($param1 = '0') twice; I bet you meant the second one to test $param2, no? Lastly, you might check the "How to Optimize your Queries" article on eXist-db's site exist-db.org/exist/tuning.xml - sections 4.3 and 4.6 are applicable.

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