Maxim Grinev <ma...@...> writes:
>
> Hi Jocelyn,
>
> we do not support nested updates in Sedna because:
> 1) it is not trivial to implement them as, for example, the nested update
> might delete the sequence over which the outer expression is iterating.
> 2) Semantic is unclear in many cases. For example, in your expression it is
> not clear what should be the result if the document exists - update cannot
> return any reasonable result because it is for side-effect.
>
> We think that it is not that bad because in all cases you can rewrite your
> query with nested update into a list of update, query and host language
> statements. For example:
> 1) run the query "collection('mydocs')/d...@id = '1000']...@timestamp =
> '2006-06-12T14:15:30']" from your host language program (i.e. Java) and
> analyze the result to find out whether the document exists
> 2) if the document exists, run the update statement and then the following
> query: <response><ok/></response>
> 3) if the document does not exists, run the following query:
> <collision>true</collision>
> (: also perhaps returning the modified $doc :)
>
> In many practical cases you can rewrite a query with nested update into a
> list of updates and a query without using host language statements if you
> slightly modify the logic of the query. We have a number of quite complex
> applications where we have avoided using any host language and nested
> updates.
>
> If you have problems to rewrite some query, let us know and we will help you
> or tell you that it is impossible without using a host language.
>
> Maxim
>
> > -----Original Message-----
> > From: sedna-discussion-boun...@... [mailto:sedna-
> > discussion-boun...@...] On Behalf Of Raymond, Jocelyn
> > Sent: Tuesday, June 13, 2006 7:53 PM
> > To: sedna-discuss...@...
> > Subject: [Sedna-discussion] Conditional replace (update)
> >
> > Hi Sedna Team,
> > I would like to know if it is possible to do conditional replace in Sedna.
> > I was thinking along the line of the following:
> >
> > let $doc := collection('mydocs')/d...@id = '1000']...@timestamp = '2006-06-
> > 12T14:15:30']
> > return
> > <response>
> > {if($doc) then (: if the $doc exist, it means that no one else
> > changed it :)
> > UPDATE replace $doc with <new doc with new timestamp./>
> > else <collision>true</collision> (: also perhaps returning the
> > modified $doc :)
> > }
> > </response>
> >
> > What I am trying to accomplish is to avoid replacing $doc that have been
> > modified by another party (thus the timestamp). Thus I would like to
> > check if the doc did changed since the user was working on it and
> > therefore take proper action. If the timestamp is the same it means that
> > no one else changed the $doc since the last read otherwise it was
> > "saved/changed" by another user. This is a primitive "lock" mechanism but
> > essential nonetheless. I have tried several "version" of the above
> > without success yet.
> > If this is not possible in Sedna, do you have any other alternative or
> > perhaps suggestion? (NOTE: my users are on our intranet over https thus
> > we cannot know when they are modifying $doc).
> >
> > Thank you,
> > Jocelyn Raymond
> >
> > PS: I know you must be close to deliver your first stable version of Sedna
> > and must be very busy. Thus don't worry if you do not return to me right
> > away. I can't wait to see your first stable version especially indexing
> > on xs:date O. Your Team is doing a very good job!
> >
> >
> > _______________________________________________
> > Sedna-discussion mailing list
> > sedna-discuss...@...
> > https://lists.sourceforge.net/lists/listinfo/sedna-discussion
>
>
Hey Guys,
I'm not sure if I understood this correct. You wrote that nested updates in
Sedna are not supported. So it's not possible to execute a delete statement with
a condition?
I will provide a little example:
This is my xml document:
<books>
<book type="hardcover">
<title>A Burnt-Out Case</title>
<author>Graham Greene</author>
<isbn>0370014995</isbn>
<price>13.00</price>
</book>
<book type="softcover">
<title>American Psycho</title>
<author>Bret Easton Ellis</author>
<isbn>0679735771</isbn>
<price>14.00</price>
</book>
</books>
And now I want to delete the book with the title "American Psycho". I tried a
few different statements but non of them worked properly. My statements looked
like this one:
for $b in doc('books')//books/book
where $b/title = 'American Psycho'
return ( update delete $b)
Thank's!
BR, Flo
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