[rules-users] Applying rules on the data in an RDBMS

[Michael Anstis]

Sure, I agree, this would be an example:-

rule "Family smurf"
when
    MyFact( smurf == "pupa" )
    ExternalObject( ) from placeHolder.namedQuery("Smurfs")
then
    //Do something
end

If MyFact is updated in other rules the list will be refreshed "from" the
named query.

So the preference might be to load the Objects into WM first:-

rule "bootstrap"
salience -100
when
    $list : List( ) from placeHolder.namedQuery("Smurfs")
then
    for(ExternalObject o : $list ) {
        insert( o );
    }
end

rule "Family smurf"
when
    MyFact( smurf == "pupa" )
    ExtenalObject( )
then
    //Do something
end

You could also have a layer of caching between the rules and RDBMS too; so
your only performing a read from cache with the "from" keyword and not RDBMS
itself.

How you choose is obviously up to you and the volatility of your data read
from RDBMS.



2011/2/14 Mauricio Salatino <salaboy at gmail.com>

> Beware with the use of the FROM Conditional Element, because if you are
> using another fact that doesn't come from the DB and you change them, the
> FROM CE will be continuously evaluated causing the execution of tons of
> queries multiple times.
> My two cents.
> Greetings
>
> 2011/2/14 Michael Anstis <michael.anstis at gmail.com>
>
> You can access Objects from external resources using the "from" keyword (in
>> fact the use of this with Hibernate named queries is a documented use-case,
>> IIRC).
>>
>> The Objects are not however inserted into WorkingMemory using "from" are
>> should therefore be time-constant as their properties will not be included
>> in truth maintenance.
>>
>> If you require the Objects as Facts in WorkingMemory for the inference
>> engine to reason with, you can write rules using "from" that insert into
>> WorkingMemory.
>>
>>
>> On 14 February 2011 11:27, hyjshanghai <hyjshanghai at gmail.com> wrote:
>>
>>>
>>> As far as I know, Drools can only reason over facts in the working
>>> memory. It
>>> can not directly "select" from RDBMS. You have to load in all data items
>>> from the database and validate them in memory by Drools.
>>> --
>>> View this message in context:
>>> http://drools-java-rules-engine.46999.n3.nabble.com/Applying-rules-on-the-data-in-an-RDBMS-tp2468317p2491888.html
>>> Sent from the Drools - User mailing list archive at Nabble.com.
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>>
>>
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>
>
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