[Catalyst] Begginer's question about application structure

Martin Bendix martinbendix at yahoo.co.uk
Tue Nov 23 08:00:37 GMT 2010

----- Original Message ----

> From: Eden Cardim <edencardim at gmail.com>
> To: The elegant MVC web framework <catalyst at lists.scsys.co.uk>
> Sent: Tue, 23 November, 2010 0:59:18
> Subject: Re: [Catalyst] Begginer's question about application structure
> >>>>> "Martin" == Martin Bendix <martinbendix at yahoo.co.uk>  writes:
>     Martin> My model should be well separated from  the controller.
>     Martin> Most, if not all of the application  functionality should be
>     Martin> exposed via the model, so  that the Catalyst controller only
>     Martin> needs to make  simple calls to the model.  To do this, model
>     Martin>  classes should be created in 'lib/myapp', with simple
>      Martin> adapters in 'lib/myapp/Model', using
>     Martin>  Catalyst::Model::Adaptor.
> Controllers need to act as an adaptor between  the model and the
> view. So, for instance, mapping $cd->artist into a value  that's suitable
> for placing in a form field "value" attribute is the  responsibility of
> the controller (cos' when you change the UI into a CLI  switchboard, for
> instance, the mapping is going to be  different).
>     Martin> At this point, I am a little less  clear on how best to structure 
>my application.
>     Martin>  As my models will be primarily concerned with accessing the 
>database, how much 
>     Martin> database code should go in my model classes, and  how much in the 
>     Martin> DBIx::Class::ResultSet  classes?  For example, should I write a 
>method in my 
>      Martin> DBIx::Class::ResultSet classes that can add new CDs when supplied  
>with title, 
>     Martin> artist and a track list?  Or would  it be better to put this in my 
> You need to constrict the scope of  your methods as much as
> possible. That is, try not to write any code that  makes the ResultSet
> aware that it's being used in a web application. I find  that most of
> DBIC's API is well suited for being invoked directly by  the
> controller. You just need to avoid any constructs that make  the
> controller aware that there's actually a relational database behind  the
> model, because then you're free to swap out to an  alternative
> implementation. A general rule of thumb is to try to avoid  writing
> complex ->search methods in the controller, put those behind  a
> friendlier method on the ResultSet, for instance write a  resultset
> method that allows you to write $cds->released('this year')  (which you
> can implement via DatetimeX::Easy) instead of
> $cds->search({  'YEAR(me.date)' => DateTime->now->year }).
>      Martin> Data validation could be handled by HTML::FormHandler, but
>      Martin> any validation performed here won't be of much use if  I
>     Martin> later provide an alternative interface to my  application.  I
>     Martin> assume that I should therefore  delegate validation to my
>     Martin> model as well, so that the  same validation methods can be
>     Martin> used no matter what  the interface?
> I'm of the opinion that using form generators puts you  through the same
> amount of trouble than writing/validating forms by hand, so  I just dodge
> the HTML::FormHandler thing altogether, but that's just me,  YMMV.
> -- 
>      Eden Cardim             Need help with your perl Catalyst or DBIx::Class 
>     Software Engineer                  http://www.shadowcat.co.uk/catalyst/
>  Shadowcat Systems Ltd.         Want a managed development or deployment 
> http://blog.edencardim.com            http://www.shadowcat.co.uk/servers/
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Hi Eden,

Thank you for your reply.  It's good to know that so far I have been thinking 
along the right lines.

I've received some great advice so far, and your post is no exception.  
DatetimeX::Easy looks like another very useful module to add to the collection - 
yet another example of the wonders of Perl and its great community :-)




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