11:20 p.m.
According to MVEL they've added a convenience for checking the
"emptiness" of a value (see: http://mvel.codehaus.org/Value+Tests )
In MVEL you'd simply write: myMap == empty
This seemed like a MUCH cleaner way to write some of the LHS of the
rules, so I thought I'd try it out.
Given the following rule:
rule "Check Empties - Original"
when
$grabBag : MyGrabBag(someMap != null)
eval ($grabBag.getSomeMap().size() == 0)
then
end
This could be rewritten:
rule "Check Empties - Simple"
when
MyGrabBag(someMap == empty)
then
end
The IDE (Eclipse 3.4.2 w/ Drools plugin) seems to recognize "empty" is
a keyword (it makes it bold), but the drools compiler in the IDE
reports:
BuildError: Unable to create restriction '[VariableRestriction: == empty
]' for field 'someMap' in the rule 'Check Empties - Simple'
BuildError: Unable to return Declaration for identifier 'empty'
Am I assuming incorrectly that the LHS is fully MVEL compliant?
3:37 p.m.
Sometimes this is indeed not clear, so I will try to explain here. Drools
uses MVEL to resolve some expressions and semantic code. Although we would
like to make it 100% compatible and enable it to use mvel everywhere, that
is easier said than done (but we do have someone working on that).
Anytime you want to force Drools to fallback into MVEL (or java, as the
other supported dialect) you need to place your code inside an eval(). For
some well known situations, Drools does this automatically, but that is not
the case with empty.
For now, in your case, you could either do:
MyGrabBag( someMap != null, someMap.empty == true )
Or if you are using mvel as your rule dialect:
MyGrabBag( eval( someMap == empty ) )
[]s
Edson
2009/8/18 Pegram, Macon <zmpegram(a)choosehmc.com>
According to MVEL they’ve added a convenience for checking the
“emptiness” of a value (see: http://mvel.codehaus.org/Value+Tests )
In MVEL you’d simply write: myMap == empty
This seemed like a MUCH cleaner way to write some of the LHS of the rules,
so I thought I’d try it out.
Given the following rule:
*rule* "Check Empties - Original"
*when *
$grabBag : MyGrabBag(someMap != null)
*eval* ($grabBag.getSomeMap().size() == 0)
*then*
*end*
* *
This could be rewritten:
* *
*rule* "Check Empties - Simple"
*when *
MyGrabBag(someMap == *empty*)
*then*
*end*
The IDE (Eclipse 3.4.2 w/ Drools plugin) seems to recognize “empty” is a
keyword (it makes it bold), but the drools compiler in the IDE reports:
BuildError: Unable to create restriction '[VariableRestriction: == empty ]'
for field 'someMap' in the rule 'Check Empties - Simple'
BuildError: Unable to return Declaration for identifier 'empty'
Am I assuming incorrectly that the LHS is fully MVEL compliant?
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--
Edson Tirelli
JBoss Drools Core Development
JBoss by Red Hat @ www.jboss.com
3:52 p.m.
Edson,
Thanks for clarifying this. I appreciate it.
Macon
2009/8/19 Edson Tirelli <tirelli(a)post.com>
Sometimes this is indeed not clear, so I will try to explain here.
Drools uses MVEL to resolve some expressions and semantic code. Although we
would like to make it 100% compatible and enable it to use mvel everywhere,
that is easier said than done (but we do have someone working on that).
Anytime you want to force Drools to fallback into MVEL (or java, as the
other supported dialect) you need to place your code inside an eval(). For
some well known situations, Drools does this automatically, but that is not
the case with empty.
For now, in your case, you could either do:
MyGrabBag( someMap != null, someMap.empty == true )
Or if you are using mvel as your rule dialect:
MyGrabBag( eval( someMap == empty ) )
[]s
Edson
2009/8/18 Pegram, Macon <zmpegram(a)choosehmc.com>
> According to MVEL they’ve added a convenience for checking the
> “emptiness” of a value (see: http://mvel.codehaus.org/Value+Tests )
>
>
>
> In MVEL you’d simply write: myMap == empty
>
>
>
> This seemed like a MUCH cleaner way to write some of the LHS of the rules,
> so I thought I’d try it out.
>
>
>
> Given the following rule:
>
> *rule* "Check Empties - Original"
>
> *when *
>
> $grabBag : MyGrabBag(someMap != null)
>
> *eval* ($grabBag.getSomeMap().size() == 0)
>
> *then*
>
> *end*
>
> * *
>
> This could be rewritten:
>
> * *
>
> *rule* "Check Empties - Simple"
>
> *when *
>
> MyGrabBag(someMap == *empty*)
>
> *then*
>
> *end*
>
>
>
> The IDE (Eclipse 3.4.2 w/ Drools plugin) seems to recognize “empty” is a
> keyword (it makes it bold), but the drools compiler in the IDE reports:
> BuildError: Unable to create restriction '[VariableRestriction: == empty
> ]' for field 'someMap' in the rule 'Check Empties - Simple'
>
> BuildError: Unable to return Declaration for identifier 'empty'
>
>
>
> Am I assuming incorrectly that the LHS is fully MVEL compliant?
>
>
>
> _______________________________________________
> rules-users mailing list
> rules-users(a)lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
>
--
Edson Tirelli
JBoss Drools Core Development
JBoss by Red Hat @ www.jboss.com
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Pegram, Macon