[rules-users] determining what field changed

[Chris Richmond]

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-bounces at lists.jboss.org
[mailto:rules-users-bounces at 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 <crichmond at referentia.com> wrote:

> From: Chris Richmond <crichmond at referentia.com>
> Subject: [rules-users] determining what field changed
> To: "'Rules Users List'" <rules-users at lists.jboss.org>
> 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 
> 
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> 
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> 


      

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