Update functions - Error handling and counting
Hello, I am playing with XQUF in BaseX ann I encountered following problems. 1) XQuery is functional language and updating function can return empty sequence. How can I count and return result how many nodes was inserted or updated ? Example: declare %private %updating function cfv:upsertVehicles ($vehicles as node()*) as empty-sequence() { let $db := db:open("db")/cars for $v in $vehicles let $dbVehicle := $db/car[vin = $v/vin] return if (not(exists($dbVehicle))) then (insert node $v as last into $db) else if (exists($dbVehicle)) then (replace node $dbVehicle with $v) else () }; I have similar problem with error handling. How can I catch and return any error. Regards Bogdan Bogucki
Hi Bogdan,
1) XQuery is functional language and updating function can return empty sequence. How can I count and return result how many nodes was inserted or updated ?
BaseX provides the update:output function for that purpose [1]. A solution could look as follows: declare %updating function cfv:upsertVehicles( $vehicles as element(car)* ) as empty-sequence() { let $db := db:open("db")/cars let $existing := $vehicles[$db/car/vin = vin] return ( (: replace existing vehicles :) for $updated in $existing let $old := $db/car[vin = $updated/vin] return replace node $old with $updated, (: insert new vehicles :) insert node ($vehicles except $existing) into $db, (: return count :) update:output(count($vehicles)) ) };
I have similar problem with error handling. How can I catch and return any error.
Due to the semantics of XQuery Update, logical errors will be raised before your updates are eventually executed [2]. No updates will be performed if the execution is expected to fail. Best, Christian [1] http://docs.basex.org/wiki/Update_Module#update:output [2] http://docs.basex.org/wiki/XQuery_Update#Error_Messages
Hi Christian, Thank you it helps me a lot. I found that update:output-cache() is in module db. Wiki describe output-cache() in update module. Best Regards Bogdan Bogucki -----Wiadomość oryginalna----- Od: Christian Grün [mailto:christian.gruen@gmail.com] Wysłano: 24 sierpnia 2018 23:41 Do: Bogdan Bogucki DW: BaseX Temat: Re: [basex-talk] Update functions - Error handling and counting Hi Bogdan,
1) XQuery is functional language and updating function can return empty sequence. How can I count and return result how many nodes was inserted or updated ?
BaseX provides the update:output function for that purpose [1]. A solution could look as follows: declare %updating function cfv:upsertVehicles( $vehicles as element(car)* ) as empty-sequence() { let $db := db:open("db")/cars let $existing := $vehicles[$db/car/vin = vin] return ( (: replace existing vehicles :) for $updated in $existing let $old := $db/car[vin = $updated/vin] return replace node $old with $updated, (: insert new vehicles :) insert node ($vehicles except $existing) into $db, (: return count :) update:output(count($vehicles)) ) };
I have similar problem with error handling. How can I catch and return any error.
Due to the semantics of XQuery Update, logical errors will be raised before your updates are eventually executed [2]. No updates will be performed if the execution is expected to fail. Best, Christian [1] http://docs.basex.org/wiki/Update_Module#update:output [2] http://docs.basex.org/wiki/XQuery_Update#Error_Messages
I found that update:output-cache() is in module db. Wiki describe output-cache() in update module.
Thanks for the info. I have updated our documentation. The function is now called update:cache(), and the legacy function db:output-cache() will be removed in a future version of BaseX.
Hi Christian, I have question about updates. I use updating function upsertVehicles in loop. Function downloadVehicles download from url and pass to upsertVehicles function. declare %updating function cfv:downloadData () as empty-sequence() { for $URL in doc("config.xml")/urls return (cfv:downloadVehicles($URL) => cfv:upsertVehicles(), admin:write-log("Inserted: " || serialize(update:cache()))) }; When does cache is purged ? In my case cache contains information from previous iterations. If upsertVehicles fail only updates from this function are reverted. What is the scope of the PUL ? Is this query, function or all invocation chain of updating functions ? I have problem with update:cache(). What is the return type ? Sequence of items or sequence of sequence [....] of items ? When I try get one item like this: update:cache()[1] I receive error: Item expected, sequence found: (0, 0). Best Regards Bogdan Bogucki -----Wiadomość oryginalna----- Od: BaseX-Talk [mailto:basex-talk-bounces@mailman.uni-konstanz.de] W imieniu Bogdan Bogucki Wysłano: 25 sierpnia 2018 17:58 Do: 'Christian Grün' DW: 'BaseX' Temat: [basex-talk] ODP: Update functions - Error handling and counting Hi Christian, Thank you it helps me a lot. I found that update:output-cache() is in module db. Wiki describe output-cache() in update module. Best Regards Bogdan Bogucki -----Wiadomość oryginalna----- Od: Christian Grün [mailto:christian.gruen@gmail.com] Wysłano: 24 sierpnia 2018 23:41 Do: Bogdan Bogucki DW: BaseX Temat: Re: [basex-talk] Update functions - Error handling and counting Hi Bogdan,
1) XQuery is functional language and updating function can return empty sequence. How can I count and return result how many nodes was inserted or updated ?
BaseX provides the update:output function for that purpose [1]. A solution could look as follows: declare %updating function cfv:upsertVehicles( $vehicles as element(car)* ) as empty-sequence() { let $db := db:open("db")/cars let $existing := $vehicles[$db/car/vin = vin] return ( (: replace existing vehicles :) for $updated in $existing let $old := $db/car[vin = $updated/vin] return replace node $old with $updated, (: insert new vehicles :) insert node ($vehicles except $existing) into $db, (: return count :) update:output(count($vehicles)) ) };
I have similar problem with error handling. How can I catch and return any error.
Due to the semantics of XQuery Update, logical errors will be raised before your updates are eventually executed [2]. No updates will be performed if the execution is expected to fail. Best, Christian [1] http://docs.basex.org/wiki/Update_Module#update:output [2] http://docs.basex.org/wiki/XQuery_Update#Error_Messages
Hi Bogdan,
When does cache is purged ? In my case cache contains information from previous iterations.
The update:cache function is non-deterministic: It will return different results before and after items have been cached [1]. I have only used this function for a few tests and in some XQUnit test cases. I don’t think there’ll be a reasonable use for it in productive code.
What is the scope of the PUL ?
Please have a look at other available online resources first (e.g. [2,3,4]).
When I try get one item like this: update:cache()[1] I receive error: Item expected, sequence found: (0, 0).
Thanks for the hint, the static return type for this function in our code base will be fixed in our next stable snapshot. Cheers Christian [1] http://docs.basex.org/wiki/Update_Module#update:cache [2] http://docs.basex.org/wiki/XQuery_Update#Concepts [3] https://www.w3.org/TR/xquery-update-10/#dt-pending-update-list [4] http://www.xmlmind.com/tutorials/XQueryUpdate/index.html
participants (2)
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Bogdan Bogucki -
Christian Grün