3:53 a.m.
2013/1/14 Emmanuel Bernard <emmanuel(a)hibernate.org>
After letting this idea rest for a while, I still like it.
In the issue, you also proposed to go a step further and get rid of
@CrossParameterConstraint altogether. I sort of remember not being keen
on the idea to protect future evolutions on the type-safe
cross-parameter way. Have you thought about it more? What is your
opinion?
Yes, I still like the idea of having only the @Constraint annotation for
defining constraints, but one problem I see is that one can not specify
different validators for return value arrays and method argument arrays in
cases like this:
@MyCustomConstraint(validationAppliesTo = PARAMETERS)
public void foo(int p1, int p2) { ... }
@MyCustomConstraint(validationAppliesTo = ANNOTATED_ELEMENT)
public Object[] bar() { ... }
With the different annotations @Constraint and @CrossParameterConstraint,
two different validators (both parameterized with <MyCustomConstraint,
Object[]>) could be specified here. Not sure, how relevant this is in
reality, though.
An alternative would be to extend @Constraint to accommodate the
specification of generic validator(s) and/or a cross-parameter validator:
public @interface Constraint {
Class<? extends ConstraintValidator<?, ?>>[] validatedBy() default
{};
Class<? extends ConstraintValidator<?, ?>>
crossParameterValidatorType() default ConstraintValidator.class;
}
The same rules would apply, i.e. the constraint must have a
"validationAppliesTo" attribute in case validators for both cases are
specified.
Thinking about Matt's IMPLICIT suggestion a bit more, I guess we could even
limit the cases where the constraint user must actually set the
"validationAppliesTo" attribute to those cases where it can't be inferred
automatically:
//"validationAppliesTo" not required, since method is void
@MyCustomConstraint
public void foo(int p1, int p2) { ... }
//not required, since method has no parameters
@MyCustomConstraint
public Object[] bar() { ... }
//"validationAppliesTo" required if constraint has a (generic)
validator for Baz and cross-param validator for Object[]
@MyCustomConstraint(validationAppliesTo = ANNOTATED_ELEMENT)
public Baz foo(int p1, int p2) { ... }
//"validationAppliesTo" required if constraint has a (generic)
validator for Object[] and cross-param validator for Object[]
@MyCustomConstraint(validationAppliesTo = PARAMETERS)
public Object[] foo(int p1, int p2) { ... }
The ValidationTarget enum would have the values IMPLICIT (default),
ANNOTATED_ELEMENT and PARAMETERS.
WDYT?
--Gunnar
Emmanuel
On Mon 2013-01-07 23:21, Gunnar Morling wrote:
> 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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