Re: preparable vs modelDriven

[Jeromy Evans <je...@blueskyminds.com.au>]

I thought I'd quickly describe my usages and opinions of Preparable and 
ModelDriven in case it helps any one:

- As Dave described, I also prefer to keep my prepare logic with the 
main code because it's easier for others to understand.
- I do use Preparable in the cases where params-prepare-params is 
desirable: typically where the params are directly addressing a nested 
bean and the parent needs to be initialised/loaded by id first.  I avoid 
this but its valuable in those occasional cases.
 - When using ModelDriven, putting any logic inside getModel() is a bad 
idea.  This is akin to putting logic inside getters.  The model is 
always an instance variable.
 - My interpretation of the primary objective of ModelDriven is to put 
the model object at the top of the value stack rather than the action.  
Therefore it is complementary with Preparable
 - My use of ModelDriven is also rare because it can make the context of 
a JSP/FTL  harder to understand (eg. I prefer contact.firstName rather 
than firstName).  However it has proven extremely useful in some cases, 
particularly if the model is polymorphic (same action, different result, 
different model class)

cheers,
Jeromy Evans

Musachy Barroso wrote:
> Struts will by default populate parameters in your action, if you use
> ModelDriven, then you can supply the object that will be populated
> instead of the action. Implementing preparable will make struts call
> prepare() before the action is executed, or prepareX() before X() is
> executed. They are just sometimes used together to achieve certain
> things, as explained on the other emails.
>
> musachy
>
> On Jan 31, 2008 5:03 PM, Adam Hardy <ah...@cyberspaceroad.com> wrote:
>   
>> I don't think you are strictly conveying the intended usage, when you say that
>> the getModel() method will 'later' return the model. It depends how your
>> interceptor stack is ordered. In the docs, it explicitly says the
>> ModelDrivenInterceptor should come before ParametersInterceptor, as often the
>> PrepareInterceptor does.
>>
>> Both ModelDriven- and PrepareInterceptor can retrieve the model and place it in
>> instance variables on the action.
>>
>> http://struts.apache.org/2.0.11/docs/prepare-interceptor.html
>>
>> http://struts.apache.org/2.0.11/docs/model-driven-interceptor.html
>>
>> What I originally wanted to ask (whether I conveyed my question correctly is
>> another matter) was: what's the difference in intention and implementation
>> between these two?
>>
>> Thanks
>> Adam
>>
>> Roberto Nunnari on 31/01/08 18:12, wrote:
>>     
>>> The prepare() method task is to retrive the model
>>> and store it as an instance variable.
>>>
>>> The getModel() method will later return the model
>>> when asked by the framework that will put it on the
>>> value stack.
>>>
>>> Please correct me if I'm wrong.
>>>
>>>       
>>> Adam Hardy wrote:
>>>       
>>>> Dave Newton on 31/01/08 16:00, wrote:
>>>>         
>>>>> Adam Hardy <ah...@cyberspaceroad.com> wrote:
>>>>>           
>>>>>> Dave Newton on 31/01/08 15:29, wrote:
>>>>>>             
>>>>>>> Adam Hardy <ah...@cyberspaceroad.com> wrote:
>>>>>>>               
>>>>>>>> * ModelDriven: how do I get hold of my model during my action
>>>>>>>> methods? I
>>>>>>>> don't  want to get getModel() again, because that will retrieve
>>>>>>>> another
>>>>>>>> instance of the  entity and not the one that was populated by struts.
>>>>>>>>                 
>>>>>>> Lazy initialization (via null check or by setting an instance var), or
>>>>>>> config through Spring, or...
>>>>>>>               
>>>>>> If your getModel() puts the model entity on an instance variable, won't
>>>>>> that confuse the param interceptor?
>>>>>>             
>>>>> Depends on what instance variable you put it in, I suppose. One of your
>>>>> questions was how to access the model object w/o running through a
>>>>> getModel()
>>>>> method that would re-instantiate; lazily initializing an instance
>>>>> variable in
>>>>> getModel() then using that instance variable is one way of dealing
>>>>> with that.
>>>>>           
>>>> OK, that makes sense now, thanks. What I thought would be the more
>>>> obvious way of obtaining the model would be to fetch it from where
>>>> struts puts it when it calls getModel(), i.e. the value stack, however
>>>> I don't see any access methods for doing that, particulary on
>>>> ActionSupport.
>>>>         
>>
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>>     
>
>
>
>   


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