Thank you for your patience and support, Christian.
Then my second question has been answered as well. So basically, when the
XQuery execution involves multiple imports of a Java module, regardless of
packaging, BaseX may create multiple instances of the according Java class.
I slightly updated your queries as follows (it is not executable, but it shows
our current setup):
testquery.xq:
-----
import module namespace m1 = 'de.interactive_instruments.module.MyQueryModule';
import module namespace m2 = 'm2' at 'm2.xqm';
import module namespace m3 = 'm3' at 'm3.xqm';
m1:init(... some data ...),
m1:add('m1'),
m1:functionMno(),
m2:do(),
m3:do(),
m1:values()
-----
m2.xqm:
-----
module namespace m2 = 'm2';
import module namespace m1 = 'de.interactive_instruments.module.MyQueryModule';
declare function m2:do() {
... some xquery that uses a function from m1, e.g. m1:functionAbc() ...
};
-----
m3.xqm:
-----
module namespace m3 = 'm3';
import module namespace m1 = 'de.interactive_instruments.module.MyQueryModule';
declare function m3:do() {
... some xquery that uses a function from m1, e.g. m1:functionXyz() ...
};
-----
m1 is a Java module, with de.interactive_instruments.module.MyQueryModule being
the Java class that extends QueryModule.
m1 is initialised, i.e. fed with some information, using methods defined by
class MyQueryModule.
Once that is done, expressions from testquery.xq call additional methods of
MyQueryModule, either directly or indirectly (by calling functions from the
XQuery modules m2 and m3).
We end up having multiple instances, i.e. Java objects, of class MyQueryModule,
- presumably due to the multiple imports of that module - and only one of them
has been initialised with the necessary information. What we would have wanted
is a single instance/object of MyQueryModule, which has the information given
to it by calling initialisation functions in testquery.xq, and which would
therefore have this information regardless of where one of the m1 functions is
called afterwards (be it in testquery.xq, or the modules m2 and m3).
So some kind of QueryModule singleton construct would be handy, but I doubt
that would work with BaseX as-is (assuming that a default constructor is used
to create an object of MyQueryModule when one of its methods is invoked). I
guess we could also explicitly create the MyQueryModule object (as outlined in
the FileWriter example on
http://docs.basex.org/wiki/Java_Bindings#Namespace_Declarations) and pass it
around as a function parameter, but that would increase the level of complexity
in our XQuery code quite a bit, so I doubt that this would be desirable for us.
Maybe having a QueryModule implementation that acts as a façade to a singleton
which does the actual work ... but I digress.
From what I've learned so far in this conversation, we'd better just ensure
that there is only a single import of module m1.
Best regards,
Johannes
-----Ursprüngliche Nachricht-----
Von: Christian Grün [mailto:christian.gr...@gmail.com]
Gesendet: Mittwoch, 18. Dezember 2019 15:59
An: Johannes Echterhoff <echterh...@interactive-instruments.de>
Cc: BaseX <basex-talk@mailman.uni-konstanz.de>
Betreff: Re: [basex-talk] How many QueryModule instances can be created?
> It may also answer my second question, where I was referring to expath
> packaging and if that would make any difference - when compared to having a
> pure JAR with the Java classes (and required libraries). It sounds like
> expath packaging does not make a difference. Please correct me if I got this
> wrong.
Right: EXPath is just another way of packaging the code. The XQuery parser will
handle all modules equally, no matter if they have initially been packaged as
XAR or via our own packaging mechanisms.
After having read your initial mail for a second time, I noticed I may have got
your setup a little wrong. I think it will be easier to find a solution if we
manage to construct a little example that shows the behavior you reported.
Otherwise, there may be too many open questions to solve (how do you import and
initialize your Java Code? is initialization identical to creating a class
instance? is the initialization code embedded in global variables? etc).
I have attached a basic set of files that (I believe) simulates your setup.
Could you extend it for me, or comment back what I may have wrongly understood?
