[rules-users] iterating over objects in a StatelessKnowledgeSession

[Michal Bali]

Hi Mark,

I want this for a unit test. It will verify that the stateless session
contains only expected objects after execution. I don't want to write a new
query that will be used only in the unit test.

Currently it is possible to iterate over all objects in a
StatefulKnowledgeSession through its getObjects method. However it is not
supported by default on the StatelessKnowledgeSession.

I've created a custom command for getting the objects. Its execute method
looks like this:
public Iterator< ? > execute(ReteooWorkingMemory session) {
    Iterator<?> objects = session.iterateObjects( filter );
    session.getBatchExecutionResult().getResults().put(identifier, objects);
    return objects;
}

Another thing to note is that StatelessKnowledgeSession.execute(Command
command) method first executes all given commands and then calls
session.fireAllRules. So if you want to insert some objects and run a query
you'll pass some insert commands and a query command. However the query will
be executed before the fireAllRules call and so it won't return
anything.Alternatively you could pass in a fireAllRules command as
well, which will
work fine. The fireAllRules will be executed twice but that is not a big
deal.
Another issue is that the query command makes it difficult to pass in query
arguments that are known only after the rules execution. Because you have to
specify the query before the fireAllRules execution. I guess you could
create your own command and do all logic there but this is not very nice.
Just my 2c.

Best Regards,
Michal


2009/3/17 Mark Proctor <mproctor at codehaus.org>

>  Michal Bali wrote:
>
> Hi,
>
> I am trying this on trunk. There is currently no way how to iterate objects
> in a StatelessKnowledgeSession.
>
> I've tried to use the GetObjectsCommand, however when it is executes the
> result is lost in the ether :). The collection of objects is not handed back
> to the user.
>
> I guess it should probably be added to the BatchExecutionResults? It will
> then be possible to access this collection of objects.
>
> You have ot specify what it is you want as an out, either as an 'out' on an
> inserted fact or global or a query.
>
>
> Please let me know if there is a different way how to iterate over objects
> in a StatelessKnowledgeSession. I'd like to use an ObjectFilter as well.
>
> Extend the Query interface and use that to filter the iterator on a
> returned query.
>
>
> Best Regards,
> Michal
>
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