[Validator] Any plan on constraint DSL or OCL support?

bquenin · **Joined:** Fri Dec 20, 2013 4:41 pm **Posts:** 4

Hi,

Everything is in the title. Hibernate validator seems a really nice project to validate constraints however, I haven't seen any ways to express constraints using a language. It would be great to have a language support such as the OCL standard for instance.

Just wondering if it has been discussed or considered already.

Thanks,
BQ.

Gunnar · **Joined:** Sat Jan 24, 2009 12:46 pm **Posts:** 388

Hi bquenin,

Sorry for the late reply, we were all in year's end holiday mode :)

Hibernate Validator provides an API for programmatic constraint declaration (http://docs.jboss.org/hibernate/stable/validator/reference/en-US/html_single/#section-programmatic-api) which allows to declare constraints using Java ("internal DSL") like this:

Code:

ConstraintMapping constraintMapping = ...;

constraintMapping
    .type( Car.class )
        .property( "manufacturer", FIELD )
            .constraint( new NotNullDef() )
        .property( "licensePlate", FIELD )
            .ignoreAnnotations()
            .constraint( new NotNullDef() )
            .constraint( new SizeDef().min( 2 ).max( 14 ) )
    .type( RentalCar.class )
        .property( "rentalStation", METHOD )
                .constraint( new NotNullDef() );

//... bootstrap validator using mapping

There is no support for external constraint languages such as OCL (besides the XML descriptors), but it should be possible to implement an OCL parser based on the programmatic API. Personally I feel this shouldn't be part of HV core as its quite specific and would probably not be used by many people.

Out of interest, what is your use case for using OCL instead of the means of constraint declaration provided by Bean Validation and HV (annotations, XML and API)?

--Gunnar

bquenin · **Joined:** Fri Dec 20, 2013 4:41 pm **Posts:** 4

Hi Gunnar,

And thanks for your answer. I think you're right, it is definitely possible to implement an OCL parser using HV as a "resolver".

The need here is to be able to express constraints as a language, but not Java code, as a user would use it. Also, the dynamic aspect of the constraint (constraint can change over time, typically initiated by a user) is something I was looking for.

Using Java code to achieve this seems inadequate.

API could be a way, but contraints are not easily "buildable" without a dedicated language (again I speak of a user).

If you think I'm wrong, please feel free to tell me why :)

Regards,
BQ.

Gunnar · **Joined:** Sat Jan 24, 2009 12:46 pm **Posts:** 388

Hey,

I don't think there is a wrong or right answer here. It really depends on the exact use case and its circumstances.

My point is, the Java API allows to implement all sorts of "front ends" for declaring constraints on a given model in a dynamic manner. You could build an OCL parser using the API as back end, you could create a small DSL in a language such as JRuby based on top of it etc.

If you decide to implement something along these lines on your side, I'd be very interested in any insights and findings you get, i.e. does the API satisfy all the needs, where could it be improved etc.

--Gunnar