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From Matt Benson <>
Subject Re: Dynamically applied constraints
Date Thu, 24 Jun 2010 23:22:42 GMT

On Jun 24, 2010, at 6:13 PM, Gerhard Petracek wrote:

> hi,
> basically i agree with mark.
> some additions:
> there was no intention to support manipulation of bv-constraints on-the-fly.
> (that's one of the reasons why e.g. myfaces extval still provides an alternative validation-module
which supports more dynamic use-cases for jsf applications.)
> however, for "special" cases you can use e.g. group validation and/or class-level validation.
> beyond that it's possible to implement some custom mechanisms to extend the std. features
of bv or to delegate some parts of the validation-process to a different validation-engine
(e.g. via a constraint-validator which uses dependency injection).

That's more or less what I'm planning to do here.  :)


> anyway, imo it's better to discuss use-cases as well as possible solutions with concrete
examples. if there is a common scenario and we find a nice and >generic< solution for
it, we could prototype the solution in a special branch. as soon as it works we could provide
an add-on for bv. if we need e.g. a new bv-api, i would suggest it in the eg for the next
version of bv.
> @"shadow instances":
> some weeks ago i've started a discussion about transactional validation in the eg. (+
i prototyped different solutions as extval-add-on.)
> to provide a complete solution for it we would need proxies. -> we postponed the discussion.
> regards,
> gerhard
> Your JSF powerhouse -
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> 2010/6/24 Matt Benson <>
> On Jun 24, 2010, at 3:32 PM, Mark Struberg wrote:
> > Hi Matt!
> >
> Hi, Mark.  Thanks for your response (note, all, that this doesn't preclude additional
responses).  :)
> > Interesting thoughts, but I'm not sure if JSR-303 is the golden bullet for business
validations. To be honest, I personally doubt it ;)
> >
> > The thing is there is still the famous old 80:20 rule out there: 80% of the use
cases / processes take 20% of the effort, but the very little rest which is left (all the
'exceptional' cases) will cost you 80% of the whole budget (money and time wise).
> >
> Yes, I've become very familiar with that concept recently.  :)
> > Why do I do all those prays? Because I personally think that more complex business
validations should still be programmed in the business code because they are so complex that
there is no easy way to 'configure' them. Maybe it can be done by configuration, but most
probably simply coding it will be easier.
> >
> > It's like with all meta-languages: the more powerful they become, the more complex
they get. And often they grow more complex than having a general purpose programming language
+ a few small helper libraries for your special problem.
> >
> > Take for example a simple multi field cross - validation. This seems sooo easy at
the first glance, but it is _really_ hard to do it right!
> >
> > assumption: it should not be possible to set wrong values into your data beans.
> >
> > This sounds easy, because you just need to validate each field before you actually
set the value. But let's consider a bean (heavily simplified and meta coded)
> > public class BeanX {
> >  @MustBeZero if field j > 3
> >  int i;
> >
> >  @MustBeZero if field i > 3
> >  int j;
> > }
> >
> >
> > And now what happens if you like to set i=6 and j=8 ?
> > As you can see, this really depends on the order in which the fields get set.
> > You can easily set i=6 as long as j is not yet filled. But what happens then? While
trying to set j=8 the 2nd field validation fails. So this situation is obviously not allowed.
But in what state are we now? We already allowed to set i=6 which is only half of the truth!
We basically trashed our bean, because ideally it should still contain the old values and
even setting i=6 should have been revoked.
> >
> I would argue that this is an example of a misconfiguration, and nobody has any business
being upset when it fails.  ;)
> > I don't think there is a way to work around this without introducing a complete
shadow instance of the bean. But this is only the peak of the iceberg - there are sooo many
other much more difficult situations out there.
> >
> To disclose further, a shadow instance of the bean is very nearly what I am working with:
 a collection of metadata for a graph's properties (in case you're concerned about me at this
point, I will go on to disclose that they are lazily and dynamically generated wherever possible).
 In fact, I began this layer of my project with my own notion of a property constraint; I'd
just like to migrate that to be a ConstraintDescriptor and cut down on reinventions of wheels
where I can.
> > To relativate this - I now work with JSR-303 in a EE6 project since december last
year (being a really early adaptor) - and in those 80% of the cases JSR-303 eases my life
HEAVILY. I'd say the rate is even much higher - close to 98% (*). But there are still those
2% where I rather code my business rules in Java than I configure an utterly complex JSR-303
> >
> > So while having a dynamic ruleset seems cool from the first glance, I'm not sure
if the old-fashioned way of just coding it wouldn't be much easier?
> >
> What I currently have is the ability to use Java and/or Drools to apply constraints to
my graph.  So I am, as you recommend, implementing a business rule in whatever way is the
best combination of [quicker|easier|more maintainable] to _set_up_ the constraint for querying
and validation.  I honestly haven't heard anything to make me believe that, for my existing
structure, the approach I outlined before is not reasonable.
> > LieGrue,
> > strub
> >
> > (*): to make this more clear: JSR-303 really rocks, because you will get rid of
manually hacking most of the 'dumb' validation code which is always the same over and over
> >
> Strangely, I have very little to perform in the way of dumb/repetitive validations; the
vast majority of what I need is context-dependent.  I simply can't resolve myself to the notion
that ALL my validation information, of whatever complexity, should not ultimately be funneled
through a single point.  At this point you've not managed to dissuade me from my plan, though
I repeat my appreciation of your willingness to discuss it.
> -Matt
> >
> >
> > ----- Original Message ----
> >> From: Matt Benson <>
> >> To:
> >> Sent: Thu, June 24, 2010 8:47:25 PM
> >> Subject: Dynamically applied constraints
> >>
> >> Hello all--
> >  I'm just getting my feet wet with JSR-303.  I started
> >> out using hibernate-validator, but as a foundation member and general
> >> connoisseur of Apache Kool-Aid I thought the very least I could do is give bval
> >> a fair shake.  So far, just browsing code and javadocs--my typical way of
> >> acquainting myself with an OSS project--I'm impressed, FWIW.
> >
> > What I want
> >> to do is expose all my validation information to my controller/view layers per
> >> the standard APIs, and here's the catch:  *including* business-level
> >> validations which can be extremely dynamic in nature.  To be more explicit,
> >> I am in the insurance industry, which (in the US anyway) consists pretty much
> >> entirely of "special cases."
> >
> > Firstly, is this considered out of scope of
> >> "Bean Validation" (the spec)?  bval?  If so, why?--It's my feeling
> >> that the spec intends that "validation" be quite an open-ended concept.  A
> >> blanket "don't do this" would simply make me question the overall usefulness
> >> the spec.  However, it's obvious (at least, I *think* it is) that neither
> >> the annotation-based nor XML-based configuration methods can handle the dynamic
> >> application of constraints to a model.  At the same time I want to be able
> >> to use those configuration methods for the subset of validations that *can*
> >> handled so globally.
> >
> > I am thinking that I can reuse some of the
> >> underlying APIs from one of the existing Bean Validation implementations to
> >> maintain this dynamic information, then implement the ConstraintValidator for
> >> e.g.  @DynamicValidation annotation to reuse others' machinery.
> >> *This* I could configure in XML; best of both worlds.  So to put this into
> >> bval terms, I could maintain a MetaBean graph for each distinct model graph
> >> dynamically apply constraints per graph.
> >
> > This email has written itself in
> >> the sense that writing down my thoughts led to numerous edits and sculpted the
> >> above-outlined approach, which I'm tentatively feeling pretty good about, but
> >> I'd still like to get preliminary feedback from the community on the oh-shit
> >> level of the task I'm setting myself.
> >
> > Regards,
> > Matt
> >
> >
> >
> >

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