2014-05-27 19:42 GMT+02:00 Davide Sottara <dsotty@gmail.com>:

Consider that a trait is an interface applied to some class. In the context of the pair:
A "hard" field is a property (get/set) exposed by the interface AND the underlying class
A "soft" (or "virtual") field is a property exposed by the interface BUT NOT by the underlying class
A "hidden" field is a field of the underlying class NOT exposed by the interface

Hard and Soft fields can be accessed using the interface, hidden fields are accessible using the map-like
construct fields[ "fieldName" ].

This said,
the mapping is by default done using the property name and (then) the property type.
However, this mapping can be decoupled using the annotation @Alias() on either the class OR the trait.
E.g.
declare Core
name : String @Alias( "any-Id-or-even-an-IRI-here" )
end

declare trait SomeTrait
label : String @Alias( "..." ) // if two "aliases" match, this will be considered a hard field
end

The "accessor", i.e. the ability to bind a trait property to a (possibly deeply) nested path is what I'm working
on these days, I have the same requirement from another urgent use case

For the time being, you can probably create a "shortcut" accessor pair in your implementation class,
to execute the complex expression, and @Alias it to the trait field.

Please let me know if you find any issue/bugs and any feature request you may have!
Best
Davide

On 05/27/2014 07:57 AM, Horváth Péter Gergely wrote:
Hi Davide,

Drools trait functionality is one of the powerful concepts which makes Drools a good candidate for the project. So keep up the good work! :) However I'm not sure if its current level of flexibility would be sufficient for our use case. I've checked the documentation, but haven't really found the term virtual field -- could you please elaborate on this?

Do you think we could somehow hook into the evaluation of the aliases or the "fields" Map? Sometimes you would need slightly more than merely aliasing fields to something else; e.g. calculating values for the purpose of rule processing or extracting a value from a more complex object tree etc. Citing the example -- GoldenCustomer( fields[ "age" ] > 18 ) -- being able to get a reference to the target object and the field map expression "age" would be quite close to what I imagined. Our custom code could then perform the appropriate translation and return the requested value, hiding the fact whether "age" is an actual field in the Customer object itself/retrieved from an encapsulated complex object e.g. replacing expression "customer.personalInformation.birthData.age"/calculated on the flight.

What do you think?

Cheers,

Peter

2014-05-26 17:58 GMT+02:00 Davide Sottara <dsotty@gmail.com>:

We are working on the trait framework for cases like this. Essentially,
it allows to use
interfaces when writing rules AND to inject the interfaces dynamically
at runtime,
at the instance level. It relies on transparent proxies which wrap the
data classes
and implement the required interfaces. A simple field aliasing mechanism
is provided
(work in progress). For more complex transformations, "virtual" fields
can be added.
See section 7.7.8 of the manual for more details and let me know if it
can help
with your use case.
Best,
Davide

On 05/26/2014 09:55 AM, Wolfgang Laun wrote:
> Even a relatively sophisticated transformation would be easier to implement
> and most certainly safer from changes in the unstable Drools API than some
> hook-and-intercept mechanism built into Drools.
>
> Notice that violent structural departure of the model the BUs see from what
> you call "persistence model" might make it impossible for the BUs to come
> up with rules that can be transformed to match the other model at all;
> if it is possible, rules might still incur a heavy performance penalty.
>
> It is (IMHO) a myth that "Rules" is a foolproof way of establishing
> business logic
> independent from the data model and application environment with which
> this logic should be able to cooperate. As long as everything is kept in the
> abstract (i.e., formulated in terms of mathematics) it will look good, but
> any implementation may throw a spanner in the works, or worse.
>
> -W
>
> On 26/05/2014, Péter Gergely, Horváth <h.peter@mailbox.hu> wrote:
>> Hi Wolfgang,
>>
>> Thank you for your input. You are right that some of the cases could simply
>> be covered by regexp-replace, but I'm afraid, not all of them. Interfaces
>> could also help, but we have a requirement that the business rules should
>> not be tightly coupled to the underlying persistence model. (I understand
>> that some might say this is not ideal, but that is our current situation)
>>
>> I am wondering whether it is possible to hook into Drools engine and
>> intercept field value reference expression evaluations in run time (e.g if
>> "foo.bars" is used in an expression, we could return "foo.barList") ? By
>> injecting some custom code, we could make the necessary decisions and
>> extract the proper value from an object. Unfortunately these parts of
>> Drools are pretty much undocumented.
>>
>> Regards,
>> Peter
>>
>>
>>
>> 2014-05-26 13:57 GMT+02:00 Wolfgang Laun <wolfgang.laun@gmail.com>:
>>
>>> What you describe can be done with /bin/sed.
>>>
>>> Notice that the DSL processor doesn't require you to translate entire
>>> patterns; there is a mechanism for translating "keywords", which is
>>> just arbitrary tokens to whatever replacement text.
>>>
>>> If a "bar" must be translated to a "barList" in the context of a class
>>> "Foo" but not in any other context, a more sophisticated translation
>>> is required in any case (with /bin/sed still being sufficient if
>>> patterns aren't split across lines).
>>>
>>> Some say that good design makes use of Interfaces, which leaves room
>>> for actual implementations being changed as long as the interfaces are
>>> implemented. Here, note that rules can be written against interface
>>> types.
>>>
>>> -W
>>>
>>>
>>> On 26/05/2014, Péter Gergely, Horváth <h.peter@mailbox.hu> wrote:
>>>> Hi All,
>>>>
>>>> We are evaluating Drools 6 for our use case, and face challenges where
>>>> we
>>>> would need some ideas from more experienced users of Drools.
>>>>
>>>> We have an application with a massive code base and a large number of
>>> model
>>>> (entity) classes. We are in the process of moving away from inherited
>>>> legacy technologies and refactoring the old code base. As a part of
>>>> this
>>>> work we would like extract some of the hard-coded business logic to
>>>> external rules, that is why we are looking at Drools as a potential
>>>> solution.
>>>>
>>>> What we would like to have is some kind of abstraction or mapping
>>>> between
>>>> actual entities and rules the business users can define so that they do
>>> not
>>>> have to know the _exact_ details of the data model (field names,
>>>> precise
>>>> relations etc). This would be important for us so that we can refactor
>>> the
>>>> old model classes without affecting business rules; also it would make
>>> life
>>>> easier for the business users. While IDE support might make refactoring
>>>> easier, we definitely want to have a separation between rules and
>>> entities.
>>>> Given our situation, writing and maintaining "stable" wrapper/adapter
>>>> classes for the sole purpose of rule processing is out of question. I
>>> have
>>>> checked the documentation of Drools DSL support and for me it seems to
>>>> be
>>>> overkill for our use case: we do not really need a custom language, but
>>>> simply an abstraction between rules and the data model classes.
>>>>
>>>> What I could imagine is a piece of code, (a custom property resolver? -
>>> no
>>>> sure how it is called) which maps property expressions to actual
>>> properties
>>>> based on a custom annotation on the entity class or something like
>>>> that,
>>> so
>>>> that a rule containing "Foo.bars" expression does not have to change
>>>> even
>>>> if we decide to rename "Foo.bars" to "Foo.barList" in the model
>>>> classes.
>>>> (This was just a simple example of a potential use cases)
>>>>
>>>> Could you please share your thoughts on this topic and point me into
>>>> the
>>>> right direction?
>>>>
>>>> Thanks,
>>>> Peter
>>>>
>>> _______________________________________________
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>>> rules-users@lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>
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