Peter Boncz wrote:
> Hi Maurice,
>
> That is not possible.. without adding extensions such as proposed in XQueryP
> or
> XQuery-Bang.
>
> Why is it that running the update followed by a query is not acceptable?
>
Running an update followed by a query is acceptable. My point is that
the update and the query are both "requests" ... *asynchronous* requests
if you use XRPC as communication mechanism. I don't mind sending the
update and the query in separated requests, but it seems to me
inefficient and cumbersome for a developer that he needs to program it
in such a way that he sends the update, necessarily waits for it to be
completed, then sends the query and waits for the result. The developer
is not interested in the response to the update. Hence, it would be IMO
better if this developer can simply send the update, and without waiting
for it to be completed, send the query and wait for the result of the
query. In this way, he assumes however that the query 'sees' the result
of the update ... and I am not convinced that this is what he will get,
because: it is not guaranteed that the update request is received by the
server before the query request, and that the update request is finished
before the query request starts. Like I said, I'm only mimicking an
application sending "UPDATE;SELECT" to a relational database.
> Another idea is to use fn:put() in the update, and then just a HTTP GET to get
> the XML result out. That is still a single query.
>
>
Why is this a single query? I need to send one XRPC message that calls a
function in a module that does the fn:put(), and another request with
HTTP GET to get the result out ... and the application has to wait for
the response of the XRPC message, before doing the HTTP GET, right?
We are now discussing full-fledged transactions and what I would expect
from MXQ if it would support full-fledged transactions. My original
question was much simpler. I want the result of a query to be both
stored and sent back to the application. This requires 2 requests that
need to be executed serially: fn:put(query,"doc.xml") ; doc("doc.xml")
Wouldn't it be very helpful, whatever restrictions or visibility
constraints, if this simple thing could be done in one function, hence
one XRPC-request? I don't see any technical objections to allow the
XQuery expression below (i.e., remove the typing constraints) and say
that the semantics is that it results in (1) an update tape applied
afterwards, and (2) a query result (everything in the sequence that is
not an update), and hence that updates done in a query are not visible
to the query itself.
let $answer := query
return (fn:put($answer,"doc"), $answer)
This would already make live much easier for a developer in many simple
cases.
Maurice.
--
----------------------------------------------------------------------
Dr.Ir. M. van Keulen - Assistant Professor, Data Management Technology
Univ. of Twente, Dept of EEMCS, POBox 217, 7500 AE Enschede, Netherlands
Email: [EMAIL PROTECTED], Phone: +31 534893688, Fax: +31 534892927
Room: ZI 3039, WWW: http://www.cs.utwente.nl/~keulen
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