[Catalyst] Where should constraints go

[Ian Docherty]

Matt S Trout wrote:
> Ian Docherty wrote:
>> My problem is finding a clean way of getting these constraints out of 
>> the Model and into the View so that I can generate meaningful error 
>> messages without hard-coding them in the templates. By 'clean' I mean 
>> not having to code the Controller to act as the middle-man and just 
>> pass them from the Model to the View.
>>
>> Perhaps I am expecting too much.
>
> No, I understand entirely, and you aren't expecting too much at all - 
> except perhaps any expectation that this would already be fully 
> implemented :)
>
> We're doing this in Reaction using Moose to provide an introspectable 
> metamodel so the update action class reflects its constraints off the 
> model and then the form reflects its field types off the update action 
> and the fields just have the constraints "already there" when they're 
> doing validation. It's been hard work and there's a lot of hard work 
> still to come but so far it works bloody well.
>
How the hell do you find the time to work on Catalyst and on Reaction at 
the same time!!!

One thing occurs to me. What I want to do is to get parameters from the 
Model (or the Business layer) into the View via the stash. So for a User 
object I want be able to do something like.

<td align="left" class="error">Username must be between [% 
schema.user.username.min %] and  [% schema.user.username.max %] 
characters</td>

The only problem now is how to get this information from the DBIC data 
in a DRY manner.

My model namespace is not in Catalyst as in:-

MyApp::Model::DBIC::User

but is in
MyApp::Schema::User

so that I can use it outside my Catalyst application (for example in 
cron jobs) so I don't have a mechanism to do something like.

$c->forward->('MyApp::Model::DBIC::User/constraints')

Where 'constraints' would populate the stash with all the constraints 
for the User table.

The only option I can see is to do a call everywhere that I need 
constraints as follows.

$c->stash->{schema}{user} = MyApp::Model::DBIC::User::Constraints();

And in there do the following.

sub Constraints {
    return {
       username => {
          min   => 0,
          max   => 16,
       },
       firstname => {
          min   => 0,
          max   => 32,
       },
    };
}

Carl Franks has proposed a method using 'columns_info_for' which I will 
have to give some more thought to and this may remove my worry that by 
doing the above I am not doing it in a DRY manner.