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,
Quoted text · Bogdan Bogucki · 1 line
> 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))
)
};Quoted text · Bogdan Bogucki · 1 line
> 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 at 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,
Quoted text · Christian Grün · 1 line
> 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))
)
};Quoted text · Christian Grün · 1 line
> 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
Quoted text · Bogdan Bogucki · 1 line
> 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 at 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 at 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,
Quoted text · Bogdan Bogucki · 1 line
> 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))
)
};Quoted text · Bogdan Bogucki · 1 line
> 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,
Quoted text · Bogdan Bogucki · 1 line
> 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.
Quoted text · Bogdan Bogucki · 1 line
> What is the scope of the PUL ?
Please have a look at other available online resources first (e.g. [2,3,4]).
Quoted text · Bogdan Bogucki · 2 lines
> 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
Written for BaseX 9.0. BaseX may have changed since: please check the current documentation.