FLWOR expression order is lost

> basex 'declare function local:nodes() {let $data := (<test a="2"/>, <test a="1"/>) let $nodes := trace(for $n in $data order by xs:integer($n/@a/data()) return $n) return $nodes }; local:nodes()/@a/data()'

> I noticed that the order of my FLWOR expression is not kept when I do an > xpath on the node list: > >> basex 'declare function local:nodes() {let $data := (<test a="2"/>, <test >> a="1"/>) let $nodes := trace(for $n in $data order by >> xs:integer($n/@a/data()) return $n) return $nodes }; >> local:nodes()/@a/data()' > > <test a="1"/> > > <test a="2"/> > > 2 > > 1 > > > I would expect it to return it in order. > Is it a bug or or some optimization allowed by XQuery? > > I tried it on the latest snapshot (BaseX90-20171020.102055.zip). > > Best regards, > Iwan

Le vendredi 20 octobre 2017 à 19:02 +0200, Christian Grün a écrit : > Hi Iwan, > > The nodes of a path expression will always be returned in document > order. See the following query as example: > > let $xml := <xml><a>2</a><a>1</a></xml> > return ( > '[A]', sort($xml/a), > '[B]', sort($xml/a) / self::node() > ) > > The result in BaseX is: > > [A] > <a>1</a> > <a>2</a> > [B] > <a>2</a> > <a>1</a> > > While the results of the first sort function will be in the order you > would expect, the nodes of the second result were reordered. > > The order of nodes that occur in distinct XML tree (such as in your > example) is implementation-defined, so it could happen that another > query processor returns "1" before "2". However, the reason would not > be that your sorting was preserved. Instead, it would reflect another > internal ordering of the elements that you assigned to $data. More > information on the document order can be found in the spec [1]. > > You can use the map operator to get rid of the implicit reordering > step. In addition, it will be more efficient: > > local:nodes() ! @a ! data() > > Hope this helps, > Christian > > [1] https://www.w3.org/TR/xquery-31/#id-document-order > > > > > I noticed that the order of my FLWOR expression is not kept when I > > do an > > xpath on the node list: > > > > > basex 'declare function local:nodes() {let $data := (<test > > > a="2"/>, <test > > > a="1"/>) let $nodes := trace(for $n in $data order by > > > xs:integer($n/@a/data()) return $n) return $nodes }; > > > local:nodes()/@a/data()' > > > > <test a="1"/> > > > > <test a="2"/> > > > > 2 > > > > 1 > > > > > > I would expect it to return it in order. > > Is it a bug or or some optimization allowed by XQuery? > > > > I tried it on the latest snapshot (BaseX90-20171020.102055.zip). > > > > Best regards, > > Iwan

> So I should not rely on the order of a sequence (of XML trees) if I do > a path expression on it?

> Le vendredi 20 octobre 2017 à 19:02 +0200, Christian Grün a écrit : >> Hi Iwan, >> >> The nodes of a path expression will always be returned in document >> order. See the following query as example: >> >> let $xml := <xml><a>2</a><a>1</a></xml> >> return ( >> '[A]', sort($xml/a), >> '[B]', sort($xml/a) / self::node() >> ) >> >> The result in BaseX is: >> >> [A] >> <a>1</a> >> <a>2</a> >> [B] >> <a>2</a> >> <a>1</a> >> >> While the results of the first sort function will be in the order you >> would expect, the nodes of the second result were reordered. >> >> The order of nodes that occur in distinct XML tree (such as in your >> example) is implementation-defined, so it could happen that another >> query processor returns "1" before "2". However, the reason would not >> be that your sorting was preserved. Instead, it would reflect another >> internal ordering of the elements that you assigned to $data. More >> information on the document order can be found in the spec [1]. >> >> You can use the map operator to get rid of the implicit reordering >> step. In addition, it will be more efficient: >> >> local:nodes() ! @a ! data() >> >> Hope this helps, >> Christian >> >> [1] https://www.w3.org/TR/xquery-31/#id-document-order >> >> >> >> > I noticed that the order of my FLWOR expression is not kept when I >> > do an >> > xpath on the node list: >> > >> > > basex 'declare function local:nodes() {let $data := (<test >> > > a="2"/>, <test >> > > a="1"/>) let $nodes := trace(for $n in $data order by >> > > xs:integer($n/@a/data()) return $n) return $nodes }; >> > > local:nodes()/@a/data()' >> > >> > <test a="1"/> >> > >> > <test a="2"/> >> > >> > 2 >> > >> > 1 >> > >> > >> > I would expect it to return it in order. >> > Is it a bug or or some optimization allowed by XQuery? >> > >> > I tried it on the latest snapshot (BaseX90-20171020.102055.zip). >> > >> > Best regards, >> > Iwan