[rules-users] unsolved myth regarding transitive closure using insertlogical...

[Greg Barton]

Implementations of equals() and hashCode() should always agree:

http://www.javapractices.com/topic/TopicAction.do?Id=28

--- On Tue, 2/22/11, Simon Chen <simonchennj at gmail.com> wrote:

> From: Simon Chen <simonchennj at gmail.com>
> Subject: Re: [rules-users] unsolved myth regarding transitive closure using insertlogical...
> To: "Rules Users List" <rules-users at lists.jboss.org>
> Date: Tuesday, February 22, 2011, 2:24 PM
> On Sun, Feb 20, 2011 at 10:11 PM,
> Mark Proctor <mproctor at codehaus.org>
> wrote:
> > On 21/02/2011 03:03, Simon Chen wrote:
> >> On Sun, Feb 20, 2011 at 8:20 PM, Ansgar Konermann
> >> <ansgar.konermann at googlemail.com>
>  wrote:
> >>> On 19.02.2011 16:01, Simon Chen wrote:
> >>>> The example you gave seems to be the
> one-hop case. For the two-hop
> >>>> case, we need something like this
> >>>>
> >>>> when
> >>>>      edge(a, b), reach(b, c), not
> exists reach(a, c)
> >>>> then
> >>>>      insertLogical( reach(a,c) )
> >>>>
> >>>> So, where do you put your logical around?
> It should include both
> >>>> edge(a,b) and reach(b,c), right?
> >>>>
> >>>> Another thought, can we have something
> like
> >>>> testExistsAndInsertLogical() to replace
> insertLogical()? But this may
> >>>> be buggy, as the conditions are all met,
> so the rule actually fired...
> >>>>
> >>> Hi,
> >>>
> >>> from my experience, insertLogical does exactly
> what
> >>> testExistsAndInsertLogical would suggest. If
> the same object is already
> >>> in the working memory, it keeps this object
> and does not insert another
> >>> instance. This behaviour is not stated
> explicitly in the documentation,
> >>> but I did a learning test a few weeks ago and
> IIRC it clearly showed
> >>> this behaviour (at least for 5.0.1). -- I
> consider this behaviour a
> >>> feature and would like it to be kept this
> way.
> >> I am using Drools 5.1.1, and I don't think
> insertLogical prevents
> >> duplicates automatically. This also boils down to
> the question of how
> >> Drools decides whether two objects are indeed the
> same. For strings
> >> and integers, it is straightforward, but not much
> so for complex
> >> objects. Is there a way to pass in a comparison
> function?
> > InsertLogical operates on equality mode, that is
> determined by the
> > pojo's equals() method implementation. If an object
> already exists that
> > is equal, it will use that and the justification
> counter for that
> > existing object is increased.
> 
> Mark,
> 
> I did a bit debugging using the drools source code, which
> is neatly
> written btw. I now know what caused my problem. When
> logically
> inserting an object, the current implementation would
> compare the
> object with saved EqualityKeys in the
> TruthMaintenanceSystem. The
> comparison is done through hashCode(), not equals(). So, a
> duplicate
> (by value) object can be inserted, because the hashcode is
> different.
> 
> I am not sure if this is a design decision, but I would
> rather using
> equals() here. I overrode the hashCode() implementation of
> my objects,
> and it is working now...
> 
> Thanks.
> -Simon
> 
> >
> > Mark
> >>> With this, all which is necessary to implement
> transitive closure is to
> >>> remove the contradicting part of the
> precondition to avoid oscillation.
> >>> If it turns out that insertLogical does not
> perform a "does fact already
> >>> exist" check and thus might potentially insert
> duplicates, put exists( )
> >>> around the two preconditions and also use
> "exists( reach(x,y) )" to
> >>> check whether y is reachable from x.
> >> I don't quite follow. Can you elaborate with an
> actual rule?
> >>
> >> Thanks!
> >> -Simon
> >>
> >>> Kind regards
> >>>
> >>> Ansgar
> >>>
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> >>> https://lists.jboss.org/mailman/listinfo/rules-users
> >>>
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> >>
> >>
> >
> >
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> >
> 
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