We have been using BaseX 7.7 beta for a while and recently we switched to 7.8.2 and found two queries failed with the existing unit tests. After research, we found that the query is now getting compiled into a different optimized query (from 7.7) and results in evaluating a variable, even if that variable will never be used, as it is inside an IF condition for particular input. Here is the query:
------------------------------------------------------------------ declare function local:addPrefix($arg as element()?){ concat("prefix-", $arg) };
let $a := <a> <b>1</b> <b>2</b> <b>3</b> </a>
let $prefixed-data:= <ele>{local:addPrefix($a/b)}</ele>
return if (exists($a/c)) then ( $prefixed-data ) else ( 'no input data' ) ------------------------------------------------------------------
In BaseX 7.7beta the output is 'no input data' which is correct. Here $prefixed-data does not get evaluated in BaseX 7.7 beta, as exists($a/c) is FALSE. The optimized query in GUI also shows '$prefixed-data' variable removed. Here is the optimized query in BaseX 7.7 beta:
*Compiling:* - rewriting for tail calls: Q{ http://www.w3.org/2005/xquery-local-functions%7DaddPrefix - rewriting fn:exists($a/c) - inlining let $prefixed-data := element ele { (local:addPrefix($a/b)) } - removing variable $prefixed-data *Optimized Query: * declare function local:addPrefix($arg as element()?) { fn:concat("prefix-", $arg) }; let $a := element a { (element b { ("1") }, element b { ("2") }, element b { ("3") }) } return if($a/c) then element ele { (local:addPrefix($a/b)) } else "no input data"
------------------------------------------------------------------
In BaseX 7.8.2 the query throws an error.
In 7.8.2, $prefixed-data gets evaluated even though the 'IF" condition is FALSE. See optimized query from GUI here:
*Error:* Stopped at C:/source/perforce/PSODepot/health-analyzer/ha-rel504/libs/catalog/src/main/resources/analysis/vsphere/6.5/CO-001/file3, 1/18: [XPTY0004] Cannot treat item() sequence as element()?: (<b>...</b>, <b>...</b>, <b>...</b>). Compiling: - inlining Q{http://www.w3.org/2005/xquery-local-functions%7DaddPrefix#1 - inlining let $arg_3 as element()? := $a_1/b - simplifying flwor expression - rewriting fn:exists($a_1/c) *Query:* declare function local:addPrefix($arg as element()?){ concat("prefix-", $arg) }; let $a := <a> <b>1</b> <b>2</b> <b>3</b> </a> let $prefixed-data:= <ele>{local:addPrefix($a/b)}</ele> return if (exists($a/c)) then ( $prefixed-data ) else ( 'no input data' ) *Optimized Query:* let $a_1 := element a { (element b { ("1") }, element b { ("2") }, element b { ("3") }) } let $prefixed-data_2 := element ele { (fn:concat("prefix-", ((: element()?, true :) $a_1/b))) } return if($a_1/c) then $prefixed-data_2 else "no input data" Query plan: <QueryPlan> <GFLWOR> <Let> <Var name="$a" id="1"/> <CElem> <QNm value="a" type="xs:QName"/> <CElem> <QNm value="b" type="xs:QName"/> <Str value="1" type="xs:string"/> </CElem> <CElem> <QNm value="b" type="xs:QName"/> <Str value="2" type="xs:string"/> </CElem> <CElem> <QNm value="b" type="xs:QName"/> <Str value="3" type="xs:string"/> </CElem> </CElem> </Let> <Let> <Var name="$prefixed-data" id="2"/> <CElem> <QNm value="ele" type="xs:QName"/> <FNStr name="concat(atom1,atom2[,...])"> <Str value="prefix-" type="xs:string"/> <TypeCheck type="element()?" function="true"> <IterPath> <VarRef> <Var name="$a" id="1"/> </VarRef> <IterStep axis="child" test="b"/> </IterPath> </TypeCheck> </FNStr> </CElem> </Let> <If> <IterPath> <VarRef> <Var name="$a" id="1"/> </VarRef> <IterStep axis="child" test="c"/> </IterPath> <VarRef> <Var name="$prefixed-data" id="2"/> </VarRef> <Str value="no input data" type="xs:string"/> </If> </GFLWOR> </QueryPlan>
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We wanted to make sure that this is due to the way queries are executed differently now in BaseX 7.8.2 and not a bug in BaseX 7.8.2. Removing the unused variable makes sense for optimization purposes, so it looks like 7.7 was doing the right thing. Can you confirm please?
Thanks, Srini