[MarkLogic Dev General] weird xpath behaviour

[Geert Josten]

Hi Szabolcs,



Evan pointed out the following to me recently. / at the start of an XPath
expression is interpreted within MarkLogic as ‘collection()/’. A / within a
predicate,  however, is not. It is effectively interpreted as ‘root()/ ‘.



Kind regards,

Geert







*Van:* general-bounces at developer.marklogic.com [mailto:
general-bounces at developer.marklogic.com] *Namens *Szabolcs Illes
*Verzonden:* donderdag 23 februari 2012 13:54
*Aan:* general at developer.marklogic.com
*Onderwerp:* [MarkLogic Dev General] weird xpath behaviour



Hi,



I have seen this before, but came across again, so I thought ask this time.
Same/similar xquery but different results:



*Version 1:*



let $ids := /HorseRacingCard/Meeting[@country eq "England" and
AdvancedGoing]/@id

return (/HorseRacing/Meeting[@id = $ids] )[1]



returns expected results.



*Version 2*: Same as 1 but ids vatriable is just inlined



(/HorseRacing/Meeting[@id = /HorseRacingCard/Meeting[@country eq "England"
and AdvancedGoing]/@id ] )[1]



returns nothing [ slow, but that’s expected: ]



Other than Version 2 is NOT optimal since the expression inside the
predicate is evaluated for each sequence item, I guess it should return the
same results.



*Version 3:*

(/HorseRacing/Meeting[@id =* fn:collection()/*HorseRacingCard/Meeting[@country
eq "England" and AdvancedGoing]/@id ] )[1]



Returns expected results and it’s fast, expression is only evaluated once



Can someone shed some light why Version 2 is not returning any results?
Could it be a bug in the optimizer?



Thanks,

Szabolcs
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