Re: [hibernate-dev] On possible extensions for the validator
On Wed, 06 Oct 2010 17:53:38 +0200, Federico Mancini
<mancini_federico(a)yahoo.it> wrote:
Class level validation is something we had considered as well, but
discarded it as we considered it in a way "cheating" in our settings.
This because what actually happens, if I understood correctly, is that
the whole object is passed to the validator, at which point it is
possible to create
a validator class that has access to all properties of the object to
validate and therefore check any kind of interdependent constraints.
This however at cost of reusability and flexibility, since such class
level annotations can only be used on that specific class, and this
could easily be replaced
by an internal method in the object to validate, which can be called at
validation time.
Once you are going down this road you start breaking the idea of making
validation
an orthogonal concern. The idea is to separate validation from other
business logic. Using specific methods in the object itself introduces
dependencies between your code and the validation framework.
What we mean with cross-annotations is something much weaker. Only
the
values of the properties annotated with the same cross-annotation are
passed to the validator,
as a list, so that the validator does not know which value comes from
which property.
The disadvantage is that the set of properties to validate can only be
seen as a list of values, and what can be checked is that a certain
amount of them satisfies the contraint.
Your cross-annotation support should also be possible using Bean
Validation,
a class level validator for the type Object and some reflection code.
The advantage (which was our priority), is that normal validation
annotations (on single fields and methods) can be reused and composed
also to create cross-annotations,
remaining independet of the class, and requiring to write less code.
I think in most usecases users prefer to write class specific validators
which give
them full control what and how to validate. This might come at the costs of
some re-usability, but that's acceptable in this case.
So the question is: would cross-annotations still be interesting in
a
validator where we have class level validation, or would it be only
redundant?
Not sure if it is worth the added complexity. Another concern is that
purely by looking
at the validation annotations you don't know that you are having a
property or
a cross annotation constraint.
--Hardy