Wolfgang,

   As you know, there are a ton of problems when you go down the "date" route. Probably the reason java never had a decent built-in date framework (fingers crossed for JSR-310).

   Anyway, back to the point, the syntax sugar for string-based strings is a really simple way for people to use really simple dates in their rules. But, yes, with that, you can't define which calendar, timezone, daylight savings, etc, rules should use. It will just use the defaults for the JVM instance. You will probably never see *me* using that. But there are people that just want something that simple and in this case, it is there.

   MVEL page is:

http://mvel.codehaus.org/

   I don't think that mvel has anything specific to dates, but I might be wrong.

   The only thing "not available" in Drools are the control structures (if/while/etc) that we disable explicitly.

    Edson

2009/11/8 Wolfgang Laun <wolfgang.laun@gmail.com>
For the sake of clarification: Are you saying that there is, or should be, some magic which would make a constraint like

   Map ( this["departureDate"] == "07-Jan-2009" )
behave as a comparison between two java.util.Date values if the LHS Object is of this type? And also if it is a GregorianCalendar object?

Since even you are "not sure" regarding MVEL: What is the definite reference for MVEL in Drools? I have a vague recollection of reading somewhere that not all of MVEL is available...

-W


2009/11/8 Edson Tirelli <ed.tirelli@gmail.com>


     Ok, without discussing the merits of using (or not) maps, the reason you are having problems with dates is that the "string-based" date is syntax sugar in Drools parser/compiler. Although, when you create expressions using nested accessors or [] for collection/map element access, drools wraps the whole thing into an "eval" and delegates to MVEL. We do some transformations to bridge the gap between drools operators and mvel operators, but I don't think drools has anything to "transform" the string-based date into something mvel understands.

     Having said that, we should probably add this functionality to the "MVELDumper" class for better integration. Would you please open a jira for that? Also, patches are welcome in case someone would like to help. This is an isolated part of the code and easy to understand.

    Meanwhile, best you can do is avoid the use of this Map syntax + string-based dates, or write your expressions directly in a way the mvel understands (not sure mvel has a special syntax for dates).
 
    Same explanation for the NPE.

    Edson

2009/11/8 Leonardo Gomes <leonardo.f.gomes@gmail.com>

Hi Wolfgang,

Here's the context:

We're replacing a very basic home-made rule engine with drools. Today,
fact data can be added dynamically b/c for all rules our fact is
nothing more than a Map and we can register new fact data through an
UI where you say what's the key and what's the type of the value.
Rules can also be created dynamically and operate against those newly
created attributes of my fact.

Incoming requests are key / value structures and we have a service
that will look at the list of registered fact data and try to find
that information in the incoming request by looking for the keys and
getting the corresponding values, then populating the Map I just
talked about which will be injected in the working memory for
evaluation against our rules.

That's why, in Drools, I need to have my rules accessing data from a
Map. By using MVEL, as I said, it works fine with strings, integers
and list of strings, but I'm having problems with dates and would like
some advice on that case.

Here's another example of things that work:

rule "test rule"
       when
               Map ( this["airportCode"] == "GIG"
                       , this["numberOfPassengers"] > 1
                       , this["class"] in ("BUSINESS", "FIRST CLASS") )
       then
               m.addMessage("rule matched");
end

And here's where I have problems,

Map ( this["departureDate"] ) == "07-Jan-2009" )


Thanks a lot,
Leo.



On Sun, Nov 8, 2009 at 10:56 AM, Wolfgang Laun <wolfgang.laun@gmail.com> wrote:
> On Sat, Nov 7, 2009 at 6:00 PM, Leonardo Gomes <leonardo.f.gomes@gmail.com>
> wrote:
>>
>> Hello,
>>
>> I'm feeding my working memory with Maps (unfortunately, this is a
>> requirement and I can't use beans).
>>
>
> Before people start racking their brains to overcome all the resulting
> difficulties: Could you please explain what this requirement is meant to
> achieve?
> -W
>
>
>>
>> To access the values in this maps I use the following MVEL expression :
>>
>>                Map ( this["airportCode"] == "GIG"
>>                        , this["numberOfPassengers"] > "1"
>>                        , this["class"] memberOf ("BUSINESS", "FIRST") )
>>
>> And it works fine, except for dates where I get a ClassCastException,
>> even tough I'm using the right pattern:
>>
>> Map ( this["departureDate"] > "07-Nov-2009" )   --- fails
>>
>> Is there anything I need to do to make the dynamic cast of dates work,
>> in this particular case?
>>
>> --
>>
>> Morever, I get NPEs if there's no value for a given key. For example,
>> the expression Map ( this ["name"] == 'Leonardo' ) would fail if
>> there's no entry with "name" as the key.
>>
>> Any help is welcome!
>>
>> Thanks in advance,
>> Leo.
>> _______________________________________________
>> rules-users mailing list
>> rules-users@lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>
>

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--
 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @ www.jboss.com

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--
 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @ www.jboss.com