[bv-dev] Specifying no validator for cross-param constraint

[Gunnar Morling]

2013/2/8 Emmanuel Bernard <emmanuel at hibernate.org>

> Remember that I some point we discussed the ability to associate a
> constraint and its implementation via a registry or service locator
> mechanism.
> https://hibernate.onjira.com/browse/BVAL-252
>
> In that environment, the idea of a mandatory validatedBy element on
> @CrossParameterConstraint is not very appealing. We could:
>
> - make it an array but it's really the 0 or 1 semantic we are looking
>   for
> - accept any class so that we can use void.class as default value
> - use the @Validates approach
>

@Validates seems the best from these to me, as the other options change the
semantics/type-safety of the API.

I'm also starting to like the idea, that there is one way to define a
constraint annotation type (annotate it with @Constraint), while everything
related to the supported types is handled in the validator implementation.


>
> Emmanuel
>
> On Fri 2013-02-08 16:10, Hardy Ferentschik wrote:
> > Hi,
> >
> > Is this not where 'include-existing-validators="true"' in the XML config
> comes into play as well?
> > So it is still possible to configure via XML with the default constraint
> implementation in- or excluded.
> > I don't see a need for a provided NoOpValidator provided by the API. If
> you don't want to provide a
> > actual implementation you can create your own dummy.
> >
> > I still against option #1. So I guess I reasoned myself into #3
> >
> > --Hardy
> >
> >
> >
> >
> > On 8 Jan 2013, at 2:56 PM, Gunnar Morling <gunnar at hibernate.org> wrote:
> >
> > > All,
> > >
> > > I just noticed that it's currently not possible to specify *no*
> validator type for cross-parameter constraints:
> > >
> > > @CrossParameterConstraint(validatedBy=...)
> > > MyCrossParamConstraint{ ... }
> > >
> > > Not specifying a validator might be relevant for people who want to
> hide their validator implementations and e.g. configure them via XML. Null
> is not allowed as annotation member value, and it's also not possible to
> specify ConstraintValidator.class as dummy value (doesn't compile).
> > >
> > > Note that the problem doesn't exist with @Constraint where
> validatedBy() expects an array of class objects, allowing empty arrays. The
> following solutions come to my mind:
> > >
> > > #1 Get rid of @CrossParameterConstraint, use @Validates on validator
> implementations, as discussed as alternative before
> > >
> > > #2 Offer a dummy NoOpValidator in the API, obviously rather inelegant
> > >
> > > #3 Ignore the problem, maybe the use case is really uncommon? If
> required, recommend people to use their own dummy validator and override it
> via XML
> > >
> > > On a related note, if sticking to @CrossParameterConstraint, we may
> consider to narrow the type of supported validators:
> > >
> > >     public @interface CrossParameterConstraint {
> > >         Class<? extends ConstraintValidator<?, Object[]>>
> validatedBy();
> > >     }
> > >
> > > I.e., only validators for Object[] would be allowed (currently that's
> demanded by the JavaDocs only).
> > >
> > > Any thoughts?
> > >
> > > --Gunnar
> > >
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> >
> >
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