8:37 a.m.
To avoid misunderstandings: yes, equals() is written according to hashCode,
i.e., according to the usual Java conventions.
If
- an object of class Two contains a member of class One, and
- one object Two and one object One are facts, and
- a rule modifies One, changing its hashCode
then
another rule containing the patterns
$one: One()
$two: Two( $x: one == $one )
does NOT fire (any more).
If you use the constraint
one == $one || != $one
the rule will fire, and you can observe that hashCode results for $one and
$x are the same and that $one.equals( $x ) returns true.
Reproduced using 5.1.1 and 5.2.x
-W
3:37 p.m.
As One is a field of Two. When you change One you are also changing Two,
so you most notify the engine for Two too.
MArk
On 22/06/2011 14:37, Wolfgang Laun wrote:
To avoid misunderstandings: yes, equals() is written according to
hashCode, i.e., according to the usual Java conventions.
If
- an object of class Two contains a member of class One, and
- one object Two and one object One are facts, and
- a rule modifies One, changing its hashCode
then
another rule containing the patterns
$one: One()
$two: Two( $x: one == $one )
does NOT fire (any more).
If you use the constraint
one == $one || != $one
the rule will fire, and you can observe that hashCode results for $one
and $x are the same and that $one.equals( $x ) returns true.
Reproduced using 5.1.1 and 5.2.x
-W
_______________________________________________
rules-dev mailing list
rules-dev(a)lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-dev
1:03 a.m.
Eeek!
Assume this: A is a field of B is a field of C is a field of D is a...
Object references remain the same, in all objects; I simply modify A, and
"when you change [A] you are also changing [B], so I must notify the
engine for [B]" but that's a field of C... D... E... and so on, until
'I' for infinity?!
*It's just a change in some fact object's hashCode that causes this problem.
*
-W
On 22 June 2011 22:37, Mark Proctor <mproctor(a)codehaus.org> wrote:
As One is a field of Two. When you change One you are also changing
Two,
so
you most notify the engine for Two too.
MArk
On 22/06/2011 14:37, Wolfgang Laun wrote:
To avoid misunderstandings: yes, equals() is written according to
hashCode,
i.e., according to the usual Java conventions.
If
- an object of class Two contains a member of class One, and
- one object Two and one object One are facts, and
- a rule modifies One, changing its hashCode
then
another rule containing the patterns
$one: One()
$two: Two( $x: one == $one )
does NOT fire (any more).
If you use the constraint
one == $one || != $one
the rule will fire, and you can observe that hashCode results for $one and
$x are the same and that $one.equals( $x ) returns true.
Reproduced using 5.1.1 and 5.2.x
-W
_______________________________________________
rules-dev mailing list
rules-dev(a)lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
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3:24 a.m.
On 23/06/2011 07:03, Wolfgang Laun wrote:
Eeek!
Assume this: A is a field of B is a field of C is a field of D is a...
Object references remain the same, in all objects; I simply modify A, and
"when you change [A] you are also changing [B], so I must notify the
engine for [B]" but that's a field of C... D... E... and so on, until
'I' for infinity?!
_*/It's just a change in some fact object's hashCode that causes this
problem./*_
If you don't want any indexing in your rule engine. If you want
indexing, you have to notify the engine. Changes to nested accessors
have always been invisible to the engine. If a nested access changes,
you must notify the engine of the root fact.
Mark
-W
On 22 June 2011 22:37, Mark Proctor <mproctor(a)codehaus.org
<mailto:mproctor@codehaus.org>> wrote:
> As One is a field of Two. When you change One you are also changing
Two, so
> you most notify the engine for Two too.
>
> MArk
> On 22/06/2011 14:37, Wolfgang Laun wrote:
>
> To avoid misunderstandings: yes, equals() is written according to
hashCode,
> i.e., according to the usual Java conventions.
>
> If
>
> - an object of class Two contains a member of class One, and
> - one object Two and one object One are facts, and
> - a rule modifies One, changing its hashCode
>
> then
>
> another rule containing the patterns
> $one: One()
> $two: Two( $x: one == $one )
>
> does NOT fire (any more).
>
> If you use the constraint
> one == $one || != $one
> the rule will fire, and you can observe that hashCode results for
$one and
> $x are the same and that $one.equals( $x ) returns true.
>
> Reproduced using 5.1.1 and 5.2.x
>
> -W
>
>
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
_______________________________________________
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3:32 a.m.
If I have
class Type {
int field;
setField( int f ){ field = f; }
}
and do
modify( $type ){ setField( 42 ) }
where is there a "nested accessor"?
-W
On 23 June 2011 10:24, Mark Proctor <mproctor(a)codehaus.org> wrote:
**
On 23/06/2011 07:03, Wolfgang Laun wrote:
Eeek!
Assume this: A is a field of B is a field of C is a field of D is a...
Object references remain the same, in all objects; I simply modify A, and
"when you change [A] you are also changing [B], so I must notify the
engine for [B]" but that's a field of C... D... E... and so on, until
'I' for infinity?!
*It's just a change in some fact object's hashCode that causes this
problem.*
If you don't want any indexing in your rule engine. If you want indexing,
you have to notify the engine. Changes to nested accessors have always been
invisible to the engine. If a nested access changes, you must notify the
engine of the root fact.
Mark
-W
On 22 June 2011 22:37, Mark Proctor <mproctor(a)codehaus.org> wrote:
> As One is a field of Two. When you change One you are also changing Two,
so
> you most notify the engine for Two too.
>
> MArk
> On 22/06/2011 14:37, Wolfgang Laun wrote:
>
> To avoid misunderstandings: yes, equals() is written according to
hashCode,
> i.e., according to the usual Java conventions.
>
> If
>
> - an object of class Two contains a member of class One, and
> - one object Two and one object One are facts, and
> - a rule modifies One, changing its hashCode
>
> then
>
> another rule containing the patterns
> $one: One()
> $two: Two( $x: one == $one )
>
> does NOT fire (any more).
>
> If you use the constraint
> one == $one || != $one
> the rule will fire, and you can observe that hashCode results for $one
and
> $x are the same and that $one.equals( $x ) returns true.
>
> Reproduced using 5.1.1 and 5.2.x
>
> -W
>
>
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
_______________________________________________
rules-dev mailing
listrules-dev@lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
rules-dev mailing list
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https://lists.jboss.org/mailman/listinfo/rules-dev
3:50 a.m.
On 23/06/2011 09:32, Wolfgang Laun wrote:
If I have
class Type {
int field;
setField( int f ){ field = f; }
}
and do
modify( $type ){ setField( 42 ) }
where is there a "nested accessor"?
$one: One()
$two: Two( $x: one == $one )
If you change a field on object "one". that field is a nested accessor
to Two.
one.field1 = "x"
is the same as doing
two.one.field1 = "x"
so to "two" changing the field of 1 is a nested accessor.
Think about how indexing works.
left == right
when two objects are == each other indexing creates a bucket for the
left and a bucket for the right. If you change the hashcode of the one
on the right, how will it find the bucket on the left?
Mark
-W
On 23 June 2011 10:24, Mark Proctor <mproctor(a)codehaus.org
<mailto:mproctor@codehaus.org>> wrote:
On 23/06/2011 07:03, Wolfgang Laun wrote:
> Eeek!
>
> Assume this: A is a field of B is a field of C is a field of D is
> a...
>
> Object references remain the same, in all objects; I simply
> modify A, and
> "when you change [A] you are also changing [B], so I must notify the
> engine for [B]" but that's a field of C... D... E... and so on,
> until
> 'I' for infinity?!
>
> _*/It's just a change in some fact object's hashCode that causes
> this problem./*_
If you don't want any indexing in your rule engine. If you want
indexing, you have to notify the engine. Changes to nested
accessors have always been invisible to the engine. If a nested
access changes, you must notify the engine of the root fact.
Mark
>
> -W
>
>
>
> On 22 June 2011 22:37, Mark Proctor <mproctor(a)codehaus.org
> <mailto:mproctor@codehaus.org>> wrote:
> > As One is a field of Two. When you change One you are also
> changing Two, so
> > you most notify the engine for Two too.
> >
> > MArk
> > On 22/06/2011 14:37, Wolfgang Laun wrote:
> >
> > To avoid misunderstandings: yes, equals() is written according
> to hashCode,
> > i.e., according to the usual Java conventions.
> >
> > If
> >
> > - an object of class Two contains a member of class One, and
> > - one object Two and one object One are facts, and
> > - a rule modifies One, changing its hashCode
> >
> > then
> >
> > another rule containing the patterns
> > $one: One()
> > $two: Two( $x: one == $one )
> >
> > does NOT fire (any more).
> >
> > If you use the constraint
> > one == $one || != $one
> > the rule will fire, and you can observe that hashCode results
> for $one and
> > $x are the same and that $one.equals( $x ) returns true.
> >
> > Reproduced using 5.1.1 and 5.2.x
> >
> > -W
> >
> >
> >
> >
> > _______________________________________________
> > rules-dev mailing list
> > rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> > https://lists.jboss.org/mailman/listinfo/rules-dev
> >
> >
> > _______________________________________________
> > rules-dev mailing list
> > rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> > https://lists.jboss.org/mailman/listinfo/rules-dev
> >
> >
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> https://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
rules-dev mailing list
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https://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
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4:19 a.m.
Well, you are saying that if you are using references to fact objects in
combination with constraints comparing such a reference to some other object
any (overridden) hashCode method *must not refer to mutable fields* of that
object.
Certainly: this restriction should not hurt - I'm inclined to regard mutable
hashCode methods as "suspicious" anyway.
But, nevertheless, it deserves a short paragraph in the "Expert" manual,
don't you think so?
Cheers
Wolfgang
On 23 June 2011 10:50, Mark Proctor <mproctor(a)codehaus.org> wrote:
**
On 23/06/2011 09:32, Wolfgang Laun wrote:
If I have
class Type {
int field;
setField( int f ){ field = f; }
}
and do
modify( $type ){ setField( 42 ) }
where is there a "nested accessor"?
$one: One()
$two: Two( $x: one == $one )
If you change a field on object "one". that field is a nested accessor to
Two.
one.field1 = "x"
is the same as doing
two.one.field1 = "x"
so to "two" changing the field of 1 is a nested accessor.
Think about how indexing works.
left == right
when two objects are == each other indexing creates a bucket for the left
and a bucket for the right. If you change the hashcode of the one on the
right, how will it find the bucket on the left?
Mark
-W
On 23 June 2011 10:24, Mark Proctor <mproctor(a)codehaus.org> wrote:
> On 23/06/2011 07:03, Wolfgang Laun wrote:
>
> Eeek!
>
> Assume this: A is a field of B is a field of C is a field of D is a...
>
> Object references remain the same, in all objects; I simply modify A, and
> "when you change [A] you are also changing [B], so I must notify the
> engine for [B]" but that's a field of C... D... E... and so on, until
> 'I' for infinity?!
>
> *It's just a change in some fact object's hashCode that causes this
> problem.*
>
> If you don't want any indexing in your rule engine. If you want indexing,
> you have to notify the engine. Changes to nested accessors have always been
> invisible to the engine. If a nested access changes, you must notify the
> engine of the root fact.
>
> Mark
>
>
> -W
>
>
>
> On 22 June 2011 22:37, Mark Proctor <mproctor(a)codehaus.org> wrote:
> > As One is a field of Two. When you change One you are also changing Two,
> so
> > you most notify the engine for Two too.
> >
> > MArk
> > On 22/06/2011 14:37, Wolfgang Laun wrote:
> >
> > To avoid misunderstandings: yes, equals() is written according to
> hashCode,
> > i.e., according to the usual Java conventions.
> >
> > If
> >
> > - an object of class Two contains a member of class One, and
> > - one object Two and one object One are facts, and
> > - a rule modifies One, changing its hashCode
> >
> > then
> >
> > another rule containing the patterns
> > $one: One()
> > $two: Two( $x: one == $one )
> >
> > does NOT fire (any more).
> >
> > If you use the constraint
> > one == $one || != $one
> > the rule will fire, and you can observe that hashCode results for $one
> and
> > $x are the same and that $one.equals( $x ) returns true.
> >
> > Reproduced using 5.1.1 and 5.2.x
> >
> > -W
> >
> >
> >
> >
> > _______________________________________________
> > rules-dev mailing list
> > rules-dev(a)lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-dev
> >
> >
> > _______________________________________________
> > rules-dev mailing list
> > rules-dev(a)lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-dev
> >
> >
>
>
> _______________________________________________
> rules-dev mailing
listrules-dev@lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-dev
>
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
_______________________________________________
rules-dev mailing
listrules-dev@lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
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4:28 a.m.
On 23/06/2011 10:19, Wolfgang Laun wrote:
Well, you are saying that if you are using references to fact objects
in combination with constraints comparing such a reference to some
other object any (overridden) hashCode method /*must not refer to
mutable fields*/ of that object.
hashCode method /*must not refer to mutable
fields*/ of that object.
That's not a good idea really. Hashcode's should refer to fields that
you constrain on, as a general good rule. and those fields are normally
mutable.
I don't really know what more to say than...
Nested accessors are "black box" if you modify a nested accessor you
must notify the root object(s) that are inserted into the engine.
If you want to write up some paragraphs talking people through how
hashcode's and hashmap's work. Specifiically if you change the hashcode
of an object that is in map you won't be able to find it in the map any
more - which is what is happening to you. Notification effectively takes
the root object out and put's it back in again, so it lives in the
correct index.
This is why other engines don't support Objects as fields, you can only
use values - strings, numbers etc. For them it's worse though, they have
to use techniques like shadow facts otherwise they get memory corruption
- but shadow facts only work on direct values, and cannot shadow objects
and nested fields. If you tried to do this stuff in other engines they
would just get corrupted. It's only because we do a tree-graph based
rete network for assymetrical retract that we can allow you to do this
without corruption, but you must still notify the engine.
Mark
Certainly: this restriction should not hurt - I'm inclined to regard
mutable hashCode methods as "suspicious" anyway.
But, nevertheless, it deserves a short paragraph in the "Expert"
manual, don't you think so?
Cheers
Wolfgang
On 23 June 2011 10:50, Mark Proctor <mproctor(a)codehaus.org
<mailto:mproctor@codehaus.org>> wrote:
On 23/06/2011 09:32, Wolfgang Laun wrote:
> If I have
> class Type {
> int field;
> setField( int f ){ field = f; }
> }
>
> and do
>
> modify( $type ){ setField( 42 ) }
>
> where is there a "nested accessor"?
$one: One()
$two: Two( $x: one == $one )
If you change a field on object "one". that field is a nested
accessor to Two.
one.field1 = "x"
is the same as doing
two.one.field1 = "x"
so to "two" changing the field of 1 is a nested accessor.
Think about how indexing works.
left == right
when two objects are == each other indexing creates a bucket for
the left and a bucket for the right. If you change the hashcode of
the one on the right, how will it find the bucket on the left?
Mark
>
> -W
>
> On 23 June 2011 10:24, Mark Proctor <mproctor(a)codehaus.org
> <mailto:mproctor@codehaus.org>> wrote:
>
> On 23/06/2011 07:03, Wolfgang Laun wrote:
>> Eeek!
>>
>> Assume this: A is a field of B is a field of C is a field of
>> D is a...
>>
>> Object references remain the same, in all objects; I simply
>> modify A, and
>> "when you change [A] you are also changing [B], so I must
>> notify the
>> engine for [B]" but that's a field of C... D... E... and so
>> on, until
>> 'I' for infinity?!
>>
>> _*/It's just a change in some fact object's hashCode that
>> causes this problem./*_
> If you don't want any indexing in your rule engine. If you
> want indexing, you have to notify the engine. Changes to
> nested accessors have always been invisible to the engine. If
> a nested access changes, you must notify the engine of the
> root fact.
>
> Mark
>
>>
>> -W
>>
>>
>>
>> On 22 June 2011 22:37, Mark Proctor <mproctor(a)codehaus.org
>> <mailto:mproctor@codehaus.org>> wrote:
>> > As One is a field of Two. When you change One you are also
>> changing Two, so
>> > you most notify the engine for Two too.
>> >
>> > MArk
>> > On 22/06/2011 14:37, Wolfgang Laun wrote:
>> >
>> > To avoid misunderstandings: yes, equals() is written
>> according to hashCode,
>> > i.e., according to the usual Java conventions.
>> >
>> > If
>> >
>> > - an object of class Two contains a member of class
>> One, and
>> > - one object Two and one object One are facts, and
>> > - a rule modifies One, changing its hashCode
>> >
>> > then
>> >
>> > another rule containing the patterns
>> > $one: One()
>> > $two: Two( $x: one == $one )
>> >
>> > does NOT fire (any more).
>> >
>> > If you use the constraint
>> > one == $one || != $one
>> > the rule will fire, and you can observe that hashCode
>> results for $one and
>> > $x are the same and that $one.equals( $x ) returns true.
>> >
>> > Reproduced using 5.1.1 and 5.2.x
>> >
>> > -W
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > rules-dev mailing list
>> > rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
>> > https://lists.jboss.org/mailman/listinfo/rules-dev
>> >
>> >
>> > _______________________________________________
>> > rules-dev mailing list
>> > rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
>> > https://lists.jboss.org/mailman/listinfo/rules-dev
>> >
>> >
>>
>>
>> _______________________________________________
>> rules-dev mailing list
>> rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
>> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org>
> https://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
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https://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
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8:10 a.m.
On 23 June 2011 11:28, Mark Proctor <mproctor(a)codehaus.org> wrote:
**
On 23/06/2011 10:19, Wolfgang Laun wrote:
Well, you are saying that if you are using references to fact objects in
combination with constraints comparing such a reference to some other object
any (overridden) hashCode method *must not refer to mutable fields* of
that object.
hashCode method *must not refer to mutable fields* of that object.
That's not a good idea really. Hashcode's should refer to fields that you
constrain on, as a general good rule. and those fields are normally mutable.
(Aside: Which may mean that all attributes of, say, an article - price,
storage quantity,... - should be part of the hash code, since those sure are
used in constraints?)
I don't really know what more to say than...
Nested accessors are "black box" if you modify a nested accessor you must
notify the root object(s) that are inserted into the engine.
If you want to write up some paragraphs talking people through how
hashcode's and hashmap's work. Specifiically if you change the hashcode of
an object that is in map you won't be able to find it in the map any more -
which is what is happening to you. Notification effectively takes the root
object out and put's it back in again, so it lives in the correct index.
So the warning must be written saying something like what I try to compose
below.
<warning>
- There is a fact type A with a field b of class B and
- patterns for A use constraints comparing b with "==" to some other
object of type B and
- B overrides hashCode using a field c of B and
- this field is changed in an update of some object B.
In any situation like this, it is necessary to instruct the engine that any
fact of type A containing a reference to the changed fact B has changed.
In most real-world situation, this may not be possible. Then,
- either avoid constraining on object references by replacing this with
primary key field constraints,
- or refrain from using c in hashCode.
</warning>
This is why other engines don't support Objects as fields, you can only use
values - strings, numbers etc.
Jess supports type OBJECT in a deftemplate without shadow facts, but then a
deftemplate does not override hashCode, and so the problem does not arise in
the first place.
-W
For them it's worse though, they have to use techniques like
shadow facts
otherwise they get memory corruption - but shadow facts only work on direct
values, and cannot shadow objects and nested fields. If you tried to do this
stuff in other engines they would just get corrupted. It's only because we
do a tree-graph based rete network for assymetrical retract that we can
allow you to do this without corruption, but you must still notify the
engine.
Mark
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8 comments
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participants (2)
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