Weily,
Rules are usually seen as a disjunction of conjunctions. So, your
example would require 3 rules, one for each attribute that may be null.
As a syntax sugar, there exists the OR operator, so you can write a
single rule (but internally it will continue to be 3 rules:
$s : ( Student( $startDate : startDate ->(...), examDate == null)) ||
Student( $startDate : startDate ->(...), reExamDate == null)) ||
Student( $startDate : startDate ->(...), dailyHours == null)))
Why am I emphasysing that this is just syntax sugar? Because in the
above example, if more than one of your attributes is null, the rule
will fire multiple times (once for each null attribute) as there are in
fact 3 rules internally, one for each logical branch. Also, it will
affect your variables binding. Please note that I didn't bound the null
attribute as it would be different in each logical branch. So, be
carefull that top level OR's behavior may cause surprise for those not
used to it in rules engines.
BTW, this is not a JBRules characteristic. Rete Rules engines in
general behave like that.
So, if the above matches your needed behavior, thats ok. Otherwise,
using JBRules 3.0.x you will need to use eval:
$s: Student( $startDate : startDate ->(...),
$ed : examDate,
$rd: reExamDate,
$dh: dailyHours)
eval( ($ed == null ) || ( $rd == null ) || ($dh == null ) )
I think the above is what you are trying to achieve. In 3.1, the
difference is that you will be able to put that "eval" inside the
pattern (without the eval keyword). But the effect is the same... it is
just a bit more optimized:
$s: Student( $startDate : startDate ->(...),
$ed : examDate,
$rd: reExamDate,
$dh: dailyHours,
( ($ed == null ) || ( $rd == null ) || ($dh == null ) )
)
Hope it helps.
[]s
Edson
weily li wrote:
Thanks Edson!
But I still can't find a complete workaround for current biz need:
Here Student is a complicate POJO, and there is a one-to-many mapping
between Student and exam ( we use hibernate as the data access layer).
The complete biz requirement for the question is:
we want to filter out such students, who has started the
training in last 7 days, and if he still hasn't submitted all detail
index information.
So I hope there is such a rule:
$s : (Student($startDate : startDate
->(utilService.dateWithin($startDate,(new Date()),7,
utilService.UNIT_DAY)))
&& ( Student($examDate :examDate == null)
|| Student($reExamTimes: reExamTimes == null)
|| Student($dailyHours : dailyHours == null) ));
which will tell us these students,
whose startDate is in last 7 days.
and at least one of the index,examDate, reExamTimes and dailyHours,
is null.
Could you give more suggestions for it?
Thanks!
BTW, is there such rule sample which is closer real biz world?
Best Regards
Weily
On 11/24/06, *Edson Tirelli* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Weily,
When you use AND between patterns, you are saying the engine: find
one fact that match the first pattern and find another fact that
matches
the second pattern. If you want the same fact to match more than one
"constraint", simply write all constraints inside the same pattern. I
guess this is what you are looking for:
when
$student: Student(examDate == null, $startDate : startDate
->(utilService.dateWithin($startDate,(new Date()),7,
utilService.UNIT_DAY)))
then
println("...")
end
The above will match each single fact that complies to both
constraints.
BTW, if you indeed want to match more than one fact using AND
between
patterns, you don't need to explicit writing the AND as it is already
implicit:
when
$s1 : Student(examDate == null)
$s2 : Student($startDate : startDate
->(utilService.dateWithin($startDate,(new Date()),7,
utilService.UNIT_DAY))))
then
println("...")
end
Above example will match all possible combinations of 2 facts, as
long as the first fact matches the first pattern (and it will be bound
to variable $s1) and the second fact matches second pattern (and
it will
be bound to variable $s2). The above is exactly the same of:
when
$s1 : Student(examDate == null) AND
$s2 : Student($startDate : startDate
->(utilService.dateWithin($startDate,(new Date()),7,
utilService.UNIT_DAY))))
then
println("...")
end
Regarding syntax, we are working on parser improvements just to
avoid
any confusion like the one you reported in the first e-mail, but the
semantics of conditional elements (and, or, not, exists, etc) will not
change and it is important you understand them.
Hope it helps.
[]s
Edson
weily li wrote:
> Hi ALL,
>
> Here is several test cases:
>
> facts feeded: 5 Students.
>
> 1.
> When
> Student(examDate == null);
> Then
> println("..");
> <expected>: one line printed out
> <result>: one line printed out
>
> 2.
> When
> Student($startDate : startDate
> ->(utilService.dateWithin($startDate,(new Date()),7,
> utilService.UNIT_DAY)))
> Then
> println("...")
> <expected>: three lines printed out
> <result>: three lines printed out
>
> 3.
> when
> (Student(examDate == null) and Student($startDate : startDate
> ->(utilService.dateWithin($startDate,(new Date()),7,
> utilService.UNIT_DAY))))
> then
> println("...")
> <expected>: one line printed out
> <result>: three lines printed out(same as scenario 2)
>
> 4.
> when
> $s : (Student(examDate == null) and Student($startDate : startDate
> ->(utilService.dateWithin($startDate,(new Date()),7,
> utilService.UNIT_DAY))))
> then
> println($s.get....)
>
> At scenario 4, it should assign the Student which meet all
columns to
> $s. right?
>
> Could anyone help explain how to make 'AND' work as expected?
>
> Thanks
> Best Regards
> Weily
>
>
>
--
---
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 <http://www.jboss.com>
IT executives: Red Hat still #1 for value
http://www.redhat.com/promo/vendor/
---------------------------------------------------------------------
To unsubscribe from this list please visit:
http://xircles.codehaus.org/manage_email
<http://xircles.codehaus.org/manage_email>
--
---
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
IT executives: Red Hat still #1 for value
http://www.redhat.com/promo/vendor/
---------------------------------------------------------------------
To unsubscribe from this list please visit:
http://xircles.codehaus.org/manage_email
