Simon Flack:
>I've read the section on error handling in the request cookbook, but I'd like
>to do something a bit more advanced with exception objects, and I'd like to
>let my model classes try and handle exceptions too.
>
>It's possible to achieve some of this by overriding &process in your model
>class, but it's not easy or straightforward to handle exceptions at the
>application level. Here's a contrived example of the sort of thing I'd like to
>be able to do:
>
>package My::Controller;
>use base 'Apache::MVC;
>use Maypole::Constants;
>
>use Exception::Class
> E::FAIL => {description => 'Application error'},
> E::ACCESS_DENIED => {description => 'insufficient permissions'},
> E::INVALIDARGS => {description => 'Missing or invalid arguments',
> fields => 'parameter'};
>
># ...
>
>sub error_handler {
> my ($r, $error) = @_;
>
> return ERROR unless ref $error;
> if (UNIVERSAL::isa($error, E::ACCESS_DEINED) {
> # log invalid request...
> $r->template('access_denied');
> return OK;
> } elsif (UNIVERSAL::isa($error, E::FAIL) {
> $r->template('general_failure');
> return OK;
> }
> return ERROR:
>}
>
>#----------------------------------------------
>package My::Model;
>use Maypole::Constants;
>
>sub error_handler {
> my $class = shift;
> my ($r, $error) = @_;
>
> # Just handle E_INVALIDARGS here, let controller deal
> # with everything else
> if (UNIVERSAL::isa($error, 'E::INVALIDARGS') {
> return $r->error('Invalid value for ' . $error->parameter);
> }
> return ERROR;
>}
>
>sub view :Exported {
> my ($class, $r) = @_;
>
> my $item = $r->{objects}[0];
> throw E::FAIL ('The requested resource has expired')
> if $item->expired;
> throw E::ACCESS_DENIED ('You do not have permission to access this
>resource')
> unless $r->{user}->access_level >= $item->access_level;
> throw E::INVALIDARGS (parameter => 'key')
> unless $r->param('key') =~ /^[A-F0-9]{6}$/;
>}
>
>
>I've attached a small patch to Maypole.pm that should make this work. If your
>model raises an exception, Maypole will first try and call an 'error_handler'
>method in your model class. If that doesn't exist or returns anything other
>than OK, the 'error_handler' method on the application class will be given the
>chance to handle the exception. If that doesn't exist or returns anything
>other than OK, the current default behaviour will kick in.
>
>
We discussed this a bit on IRC and we all agreed that an error_handler
would be overkill, why not just use eval() or Error.pm in your methods?
>--simonflk
>
>
>
sebastian
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