Re: [rules-users] determining what field changed
There is no functional difference between modify and update. "update" is the
new syntax. See section 3.3.3.1.3 of the expert doc:
https://hudson.jboss.org/hudson/job/drools/lastSuccessfulBuild/artifact/trunk/target/docs/drools-expert/html_single/index.html#d0e1264
(scroll down a bit)
As for general suggestions to prevent rule re-firing, there are several
options. The most general is "make your conditions the negation of your
action." In other words, the conditions say "the objects are in state A, and
not in state B yet" and state B is what you do to them in the action. So, to
modify your example:
rule "Rule1"
when
do : DataObject(FieldA > x, fieldB != value);
then
modify(do.fieldB = value)
end
So something like:
rule "Rule2"
when
do : DataObject(fieldB == value, fieldC != someValue);
then
modify(do.fieldC = someValue)
end
rule "Rule3"
when
do : DataObject(fieldC == someValToMatchForC, do.fieldA !=
someNewValueForA);
then
modify(do.fieldA = someNewValueForA)
end
So you're always telling the engine to fire the rule if the objects are in some
state, and NOT in the state you're about to put them in.
Another general pattern is to have the objects hold some artificial state (or
match them with an object that holds the artificial state) that restricts rule
firing to transitions in a certain logical path. One simple way to do this is
to have a String (or preferably an Enum) value in the object that informs the
rules what artificial state the object is in.
rule "Rule1"
when
do : DataObject(FieldA > x, state == "StageA");
then
do.setFieldB(value);
do.setStage("StageB");
update(do);
end
So something like:
rule "Rule2"
when
do : DataObject(fieldB == value, state == "StageB");
then
do.setFieldC(someValue)
do.setStage("StageC");
update(do);
end
rule "Rule3"
when
do : DataObject(fieldC == someValToMatchForC, state == "StageC");
then
do.setFieldA(someNewValueForA);
do.setStage("StageD");
update(do);
end
This isn't as restrictive as you might think.
There are also the flow control mechanisms available for rule flow and agenda
grouping, but they don't reach down to the object level. However, mattering on
how many conflicting objects you have in memory at once, they can be quite
useful for this purpose as well. (Basically, you force the entire engine into
limited processing states, instead of individual objects.)
--- On Wed, 9/16/09, Chris Richmond wrote:
> From: Chris Richmond
> Subject: Re: [rules-users] determining what field changed
> To: "'Rules Users List'"
> Date: Wednesday, September 16, 2009, 3:52 PM
> In general do you have any
> suggestions for getting around multiple update
> detects being made? In other words I have a rule to
> detect if my DataObject
> has fieldA > X and if so, then modify fieldB. Then
> another rule that checks
> if fieldB = value and then updates field C.
>
> So something like:
>
> rule "identify modified DATAOBJECT"
> when
> do : DataObject(FieldA > x);
> then
> modify(do.fieldB = value)
> end
>
> So something like:
>
> rule "identify modified DATAOBJECT"
> when
> do : DataObject(fieldB == value);
> then
> modify(do.fieldC = someValue)
> end
>
>
> rule "identify modified DATAOBJECT"
> when
> do : DataObject(fieldC ==
> someValToMatchForC);
> then
> modify(do.fieldA = someNewValueForA)
> end
>
>
>
> But of course this leads to some sort of cross product
> execution as each one
> is run all over again after another makes a change and
> ramps out of control
>
> One question. I have been using modify() and I notice
> you had explicit:
> do.setN00b(false);
> update(do);
>
> What is the difference and will that matter to my
> scenario?
>
> Thanks,
>
> Chris
>
>
> -Original Message-
> From: rules-users-boun...@lists.jboss.org
> [mailto:rules-users-boun...@lists.jboss.org]
> On Behalf Of Greg Barton
> Sent: Wednesday, September 16, 2009 10:14 AM
> To: Rules Users List
> Subject: Re: [rules-users] determining what field changed
>
> Not really. Without modifying the objects you could
> do this outside the
> rules using a WorkingMemoryEventListener, which has
> objectInserted() and
> objectUpdated() methods. Event if you can modify the
> DataObject to add an
> "I'm a new object" flag, and set it immediately on
> insertion, then you could
> do differentiate with two rules:
>
> rule "identify new DATAOBJE
Re: [rules-users] determining what field changed
In general do you have any suggestions for getting around multiple update
detects being made? In other words I have a rule to detect if my DataObject
has fieldA > X and if so, then modify fieldB. Then another rule that checks
if fieldB = value and then updates field C.
So something like:
rule "identify modified DATAOBJECT"
when
do : DataObject(FieldA > x);
then
modify(do.fieldB = value)
end
So something like:
rule "identify modified DATAOBJECT"
when
do : DataObject(fieldB == value);
then
modify(do.fieldC = someValue)
end
rule "identify modified DATAOBJECT"
when
do : DataObject(fieldC == someValToMatchForC);
then
modify(do.fieldA = someNewValueForA)
end
But of course this leads to some sort of cross product execution as each one
is run all over again after another makes a change and ramps out of control
One question. I have been using modify() and I notice you had explicit:
do.setN00b(false);
update(do);
What is the difference and will that matter to my scenario?
Thanks,
Chris
-Original Message-
From: rules-users-boun...@lists.jboss.org
[mailto:rules-users-boun...@lists.jboss.org] On Behalf Of Greg Barton
Sent: Wednesday, September 16, 2009 10:14 AM
To: Rules Users List
Subject: Re: [rules-users] determining what field changed
Not really. Without modifying the objects you could do this outside the
rules using a WorkingMemoryEventListener, which has objectInserted() and
objectUpdated() methods. Event if you can modify the DataObject to add an
"I'm a new object" flag, and set it immediately on insertion, then you could
do differentiate with two rules:
rule "identify new DATAOBJECT"
when
do : DataObject(n00b == true);
then
do.setN00b(false);
update(do);
System.err.println("DataObject assertion detected: " + do);
end
rule "identify modified DATAOBJECT"
when
do : DataObject(n00b == false);
then
System.err.println("DataObject modification detected: " + do);
end
Which would still catch a spurious modification notification on assert! At
that point the semi-risky alternative is to not call update() in the
"identify new DATAOBJECT" rule action. That way, the "identify modified
DATAOBJECT" is not immediately activated, but it would be activated the next
time update() is called on the object. I say semi-risky because it's not
often a good idea to put a WM object into a state that the rete is not aware
of, but in this case it would do what you want.
--- On Wed, 9/16/09, Chris Richmond wrote:
> From: Chris Richmond
> Subject: [rules-users] determining what field changed
> To: "'Rules Users List'"
> Date: Wednesday, September 16, 2009, 2:41 PM
>
> Is it possible
> to determine what fields from an object
> changed within a rule.
>
> So I am using
> this to determine if any DataObject has
> changed:
>
> //IDENTIFY ANY DATAOBJECT
> CHANGES
>
> rule
> "identify any DATAOBJECT"
> when
> $do :
> DataObject();
> then
> System.err.println("ANY
> DataObject change detected:" + $do);
> End
>
> However this
> also fires when any new DataObject() is
> injected into the system and the rules are fired. I
> would like to be able to
> only have a rule fire when an object is first
> created
>
> Vs. when it is
> modified and is there a way to detect what
> values of an object have changed if I dont
> explicitly know what fields
> of DataObject changed ahead of time?
>
> Thanks,
> Chris
>
> -Inline Attachment Follows-
>
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Re: [rules-users] determining what field changed
Not really. Without modifying the objects you could do this outside the rules
using a WorkingMemoryEventListener, which has objectInserted() and
objectUpdated() methods. Event if you can modify the DataObject to add an "I'm
a new object" flag, and set it immediately on insertion, then you could do
differentiate with two rules:
rule "identify new DATAOBJECT"
when
do : DataObject(n00b == true);
then
do.setN00b(false);
update(do);
System.err.println("DataObject assertion detected: " + do);
end
rule "identify modified DATAOBJECT"
when
do : DataObject(n00b == false);
then
System.err.println("DataObject modification detected: " + do);
end
Which would still catch a spurious modification notification on assert! At
that point the semi-risky alternative is to not call update() in the "identify
new DATAOBJECT" rule action. That way, the "identify modified DATAOBJECT" is
not immediately activated, but it would be activated the next time update() is
called on the object. I say semi-risky because it's not often a good idea to
put a WM object into a state that the rete is not aware of, but in this case it
would do what you want.
--- On Wed, 9/16/09, Chris Richmond wrote:
> From: Chris Richmond
> Subject: [rules-users] determining what field changed
> To: "'Rules Users List'"
> Date: Wednesday, September 16, 2009, 2:41 PM
>
> Is it possible
> to determine what fields from an object
> changed within a rule.
>
> So I am using
> this to determine if any DataObject has
> changed:
>
> //IDENTIFY ANY DATAOBJECT
> CHANGES
>
> rule
> "identify any DATAOBJECT"
> when
> $do :
> DataObject();
> then
> System.err.println("ANY
> DataObject change detected:" + $do);
> End
>
> However this
> also fires when any new DataObject() is
> injected into the system and the rules are fired. I
> would like to be able to
> only have a rule fire when an object is first
> created
>
> Vs. when it is
> modified and is there a way to detect what
> values of an object have changed if I don’t
> explicitly know what fields
> of DataObject changed ahead of time?
>
> Thanks,
> Chris
>
> -Inline Attachment Follows-
>
> ___
> rules-users mailing list
> rules-users@lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
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[rules-users] determining what field changed
Is it possible to determine what fields from an object changed within a
rule.
So I am using this to determine if any DataObject has changed:
//IDENTIFY ANY DATAOBJECT CHANGES
rule "identify any DATAOBJECT"
when
$do : DataObject();
then
System.err.println("ANY DataObject change detected:" + $do);
End
However this also fires when any new DataObject() is injected into the
system and the rules are fired. I would like to be able to only have a rule
fire when an object is first created
Vs. when it is modified and is there a way to detect what values of an
object have changed if I don't explicitly know what fields of DataObject
changed ahead of time?
Thanks,
Chris
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