Michael,
Yes, it is surelly heavier to make database calls in the LHS of a
rule when compared to handling objects in memory. Sometimes, though, it
is not possible or not worth to load your objects from the database in
advance and you need to go for loading as needed in LHS. Although, the
best would be to use "from" CE, as it caches some results and allow
Rahul to do more or less what he wants.
Example: pretend you have Power and Temperature objects, you could
do something like:
rule "Device not working (condition id = 4)"
when
alertDefinition : AlertDefinition (conditionID== 4, eid : entityID)
Power( value < 1000 ) from dao.getPower( eid )
Temperature( deviceTemp > 50, ambTemp > 40 ) from dao.getTemperature(eid)
then
log("Triggered Device not working alert for "+ eid);
end
Hope it helps,
Edson
Anstis, Michael (M.) wrote:
It seems inefficient to make calls to a database from a rule LHS as (I'm
guessing [Edson?]) that the Rete network can't be built\optimised around
an evaluated predicate (trying to use the correct language, but possibly
failing badly). Would the AlertCondition not already have these
properties populated? Making the rule simpler too:
Rule "Device not working (condition id = 4)"
when
$ac : AlertCondition (conditionId ==4, $eid : entityID,
$p : power, $at : ambTemperature)
then
log("Triggered Device not working alert for " + $eid +
", power=" + $p + ", ambient temperature=" + $at);
end
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Rahul Phadnis
Sent: 22 February 2007 21:12
To: [email protected]
Subject: [rules-users] Rule definition help
I am very new to JBoss rules and I am trying to use it
for evaluating alert conditions.
I am asserting the AlertDefinition object as a fact
into the working memory.
The rules file would define a variety of alert
condition rules.
for example
rule "Device not working (condition id = 4)"
# the if part
when
alertDefinition : AlertDefinition (conditionID
== 4,
eid : entityID)
# here i would like to get the last power
reading from device
# with id == eid
eval (dao.getPower(eid).doubleValue() < 1000)
# then get temperature from the device
eval ((dao.getTemperature(eid) != null &&
dao.getTemperature(eid) > 50)
|| (dao.getAmbTemperature(eid) != null &&
dao.getAmbTemperature(eid) > 40)
)
then
# what do we do if the rule evaluates to true
log("Triggered Device not working alert for "
+ eid);
end
Here are my questions:
1. Am using the evals correctly? Can I possibly split
this into multiple rules to make it work better?
2. Can assign dao.getTemperature(eid) to a field. The
getTemperature call is expensive and doing it twice is
not right.
Any pointer would be appreciated.
-Rahul
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--
Edson Tirelli
Software Engineer - JBoss Rules Core Developer
Office: +55 11 3124-6000
Mobile: +55 11 9218-4151
JBoss, a division of Red Hat @ www.jboss.com
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