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From Jeromy Evans <>
Subject Re: Fundamental flaw in Model-Driven?
Date Sat, 26 Apr 2008 03:51:18 GMT
Eric D Nielsen wrote:
> I've been investigating some interesting behavior regarding model-driven actions
> and found a past thread that covers the situation from late last year:
> ...
> It would seem to be a way forward exists, however.  Model Driven can be tweaked
> as follows:
>   The model driven interceptor would need to
> a) capture the raw request parameters into some storage
> b) skip the second params interceptor
> c) create a copy of the getModel object  (to ensure its detached from any
> persistence session -- need to make sure this works for other common
> persistence engines)
> d) run params/validation on this copy
> e) if no validation errors, run params on the orginal (still attached to the
> persistence session), and proceed as normal
> f) if validation errors, intercept calls to the getters for values in the raw
> request for redisplay -- need to worry about XSS issues here
> There's a lot of moving pieces, and I'm sure I'm missing some even more subtle
> interactions.  However I do think something needs to be done.  I'm interesting
> in tackling this, and am hoping for some feedback on the above outline of
> required changes.
Hi Eric,
I haven't had an opportunity to absorb your suggestion properly yet but 
thought I'd mention I agree with your line of thinking that the 
validation mechanism in particular needs to be improved. However, this 
is a general problem that also applies to rich clients; that is 
responsibility for rolling back changes to a model, and various patterns 
have developed over the years.  A temporary copy is a simple 
implementation, however within a JPA-environment automatically creating 
a clone is often infeasible or undesirable. For example, if it's 
attached to a session, this process may cause hydration of the entire 
object graph. Unless the framework is provided hints, it won't know what 
to safely/efficiently clone.

Having the framework maintain dirty flags or proxy for the model also 
seems ineffective as the JPA provider performs the exact same task, only 

The option to write straight to the model (or DTO) and performing 
validation of the model (or DTO) is a distinguishing feature of Struts 
2, but also the source of such complications. Anyway, I don't have a 
solution, but I do intend to start resolving the numerous validation 
issues in JIRA in the near future and this one is the list.

Jeromy Evans


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