[bv-dev] Distinguishing cross-parameter and generic constraints

[Matt Benson]

Hi Gunnar,
  I kind of like the idea of being able to use a single constraint
definition type for either purpose, in that it avoids forcing users through
semantic obstacles in expressing some basic concept.  I'm less enthralled
with another "magic" annotation element name, but I don't have a better
idea at the moment either.  I'm disagree with the idea that the default
'validationAppliesTo' value should be ANNOTATED_ELEMENT; I personally would
rather see a default such as IMPLICIT whose presence requires that only one
of @Constraint or @CrossParameterConstraint be present on the annotation
type.

Matt


On Fri, Jan 11, 2013 at 9:22 AM, Gunnar Morling <gunnar at hibernate.org>wrote:

> Anyone with thoughts/feedback on this?
>
> Thanks,
>
> --Gunnar
>
>
> 2013/1/7 Gunnar Morling <gunnar at hibernate.org>
>
>> Hi all,
>>
>> As per the latest spec draft, a constraint must be either a
>> cross-parameter *or* a generic constraint, but not both at the same
>> time, as otherwise it would be ambiguous whether a constraint on a method
>> refers to the method parameters or return value.
>>
>> Most of the time this does not really pose a limitation, but some
>> constraints actually might be both, cross-parameter *and* generic,
>> depending on the specific context. Examples are @ScriptAssert in Hibernate
>> Validator or generic constraints such as this:
>>
>> @EqualPasswords
>> public void register(String userName, String password, String
>> confirmedPassword) {
>> }
>>
>> @EqualPasswords
>> public class ResetPasswordRequest {
>>     String userName;
>>     String password;
>>     String confirmedPassword;
>> }
>>
>> Based on a recent BVAL issue [1], I'm proposing to introduce a special
>> constraint annotation attribute, "validationAppliesTo", allowing to specify
>> the required behavior at the usage site:
>>
>> @EqualPasswords(validationAppliesTo=PARAMETERS)
>> public void register(String username, String password, String
>> confirmPassword) {
>> }
>>
>> @EqualPasswords(validationAppliesTo=ANNOTATED_ELEMENT)
>> public class ResetPasswordRequest {
>>     String password;
>>     String confirmedPassword;
>> }
>>
>> The following rules would apply:
>>
>> * If a constraint is annotated with @Constraint and
>> @CrossParameterConstraint, it must define a member "validationAppliesTo".
>> The default value should be ANNOTATED_ELEMENT.
>> * If a constraint is annotated with only one
>> of @Constraint/@CrossParameterConstraint, defining a "validationAppliesTo"
>> member doesn't have any special effect
>> * Specifying validationAppliesTo=PARAMETERS anywhere except a method
>> causes ConstraintDeclarationException
>>
>> Any thoughts?
>>
>> --Gunnar
>>
>> [1] https://hibernate.onjira.com/browse/BVAL-340
>>
>>
>
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