[rules-dev] Constraint efficiency: (was: "New in 5.2.0" - What works, what doesn't?)

[Wolfgang Laun]

Edson,

On 6 May 2011 01:14, Edson Tirelli <ed.tirelli at gmail.com> wrote:

>
>    Wolfgang,
>
>    These are remaining bugs that must be fixed before final. Goal is to
> support free form expressions as long as they return a boolean value (for
> traditional constraints), or any value (for positional). Period.
>

(Well, as it's past 5.2.0M2...)

Given that any expression is valid, will there still be a distinction w.r.t.
efficiency, as there was with traditional constraints as opposed to eval()?
If yes, how can I tell whether a constraint expression is "good" or "bad"?

One might assume that all legacy forms will be handled as efficiently as
now, but it's possible that not only
   field == ($var + 1)
but also
   field == $var + 1
is efficient. Or, similarly,
   field == $var
and (now) also
   $var == field

But certainly not
   field - 1 == $var
Or, at least, not until some later version ;-)

I repeat this quote (from 5.2.0 Drools Introduction and General User Guide) and
my question, what does it mean? Where is this "documented"? Is this somehow
related to the efficiency issue?

<quote>
As previously we had to document the restricted limitations of a field
constraint on the LHS compared to expressions used inside of an 'eval' or
used on the RHS.
 </quote>

Wolfgang



>
>    Edson
>
> 2011/5/5 Wolfgang Laun <wolfgang.laun at gmail.com>
>
>> In the 5.2.0 Drools Introduction and General User Guide, there's section
>> 2.1.3.1, Free Form expressions in Constraints (New Parser). It contains
>> several examples:
>> #1 Person( age * 2 > $anotherPersonsAge + 2 )
>> #2 Person( addresses["home"].streetName.startsWith( "High Park" ) )
>> #3 Person( isAdult() )
>>
>> #1 does not compile: Unable to build constraint as  'age * 2' is invalid :
>> [Rule name='exa1']
>>
>> #2 works - although I'd very much prefer not to be swamped with MVEL
>> extensions unless I ask for it.
>>
>> #3 does not compile: Unable to Analyse Expression isAdult():
>> [Error: no such identifier: isAdult]
>> [Near : {... isAdult() ....}]
>>
>> Neither rule name nor line number is provided.
>>
>> Would it please be possible to have a precise statement what one *can*write as a constraint?
>>
>>
>> <quote>
>> As previously we had to document the restricted limitations of a field
>> constraint on the LHS compared to expressions used inside of an 'eval' or
>> used on the RHS.
>>  </quote>
>>
>> I'm sorry, but I do not understand the meaning of this sentence. What does
>> it mean, please?
>>
>> Cheers
>> Wolfgang
>>
>>
>
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