[bv-dev] Feature Suggestion :: Implicit constraints

[Gunnar Morling]

Hi,

2014-07-29 15:31 GMT+02:00 Richard Fanning <Richard.Fanning at fineos.com>:

>  Hi there,
>
> We are starting to use bean validation in our product and something we
> would like to do is what I’ve coined as “implicit constraints”. I’d like to
> run this by the mailing list and get your thoughts on this as a potential
> feature in the spec.
>
> The use case we have is we have a “DateTime” object which represents Date
> & Time. Our DateTime object pre-dates JDK 8 (and JodaTime).  A DateTime for
> us has some constraints
>
>
>     1. The DateTime cannot me before LOW_DATE à 01-01-1970 00:00:00
>    2. The DateTime cannot me after HIGH_DATE à 31-12-2150 23:59:59
>
>
> Not sure of the exact history of these constraints but it would seem like
> we are trying to invent a new y2k J
>
> These constraints were enforced prior to our usage of Bean Validation as
> these were burnt into the setter of generated POJO’s (domain objects) but
> now that we are moving from generated domain objects to JPA style POJO’s
> we’d like to use Bean Validation to apply the same constraints.
>
Assume we have an object which has a DateTime property as shown below
>
> *public* *class* TestObject {
>
>         *private* DateTime myDateTime;
>
>         *public* DateTime getMyDateTime() {
>                 *return* myDateTime;
>         }
>
>         *public* *void* setMyDateTime(DateTime myDateTime) {
>                 *this*.myDateTime = myDateTime;
>         }
>
> }
>
> We’d like if developers did not need to add an annotation all DateTime
> properties to constrain with the implicit constraints.. i.e.
>
> @Date
> *private* DateTime myDateTime;
>
> In our opinion this annotation serves no additional purpose and would be
> an extra onus on the developer to add this so they ensure the value meets
> internal DateTime criteria.
>
> Looking at the 1.1 spec I cannot see any way of applying constraints
> without annotating (well you can use HV XML but that would need to be done
> for all fields).. Is that correct.
>

Yes, the spec defines constraint declaration via annotations and XML.
Hibernate Validator in addition has a (public) API for programmatic
constraint declaration.

>
> I’ve managed to implement “implicit constraints” by using non-standard
> Hibernate Validator API’s (i.e. using reflection I added an additional
> MetaDataProvider which added ConstrainedElements ( to the
> BeanConfiguration)). I can share this on GitHub is anyone is interested in
> taking a look.
>

You should better use the HV constraint API for this [1]. You could inspect
your beans using reflection and define a @Date constraint for each DateTime
property you find. MetaDataProvider et al. are internal APIs which may
change without notice between releases.

Standardizing this API might be a useful addition as it allows to implement
cases as yours in a portable manner. Not sure whether the spec should
explicitly support this requirement, as it may be very specific.

Appreciate any feedback you might have.
>
> Thanks
>
> Rich
>

--Gunnar

[1]
http://docs.jboss.org/hibernate/validator/5.1/reference/en-US/html_single/#section-programmatic-api


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