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From Mark Struberg <>
Subject Re: Dynamically applied constraints
Date Fri, 25 Jun 2010 10:06:32 GMT
Hi Matt!

Prelude: The more discussion and different thoughts are brought up early, the better we all
will do in the end. So your valueable input is highly welcome!

For the shadow objects: this is not so easy to accomplish, think about what happens if this
is a deeply nested JPA object which contains lots of 1:n relations which contain themselfs
other relations, etc. Some of them are lazy loaded, some of them eagerly fetched, preloaded,
... An unconditional deep copy might not be possible in this case (or doesn't make sense from
a performance perspective) and a simple toplevel copy might not be enough for some cases.


----- Original Message ----
> From: Matt Benson <>
> To:
> Sent: Thu, June 24, 2010 10:57:48 PM
> Subject: Re: Dynamically applied constraints
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 ruleset.
> 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 again...

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.


> ----- Original Message 
> ----
>> From: Matt Benson <
> href="">>
>> To: 
> href="">
> 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 of 
>> 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* be 
>> 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 an 
> 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 and 
>> 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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