Monday, April 23, 2007


I was not quite happy with the information efficiency of the solution Matt proposed as an answer to my previous post. It still used three attributes - and simplification of the usage of the library by reducing the number of attributes was my main goal in this quest. But it showed that indeed it needs just a bit of tweaking to get there and with some more help from the core Cat devs I did that tweaking and went down to just to attributes: PathArgs - for declaring the number of parameters to be taken from the path and EndPoint - to declare an action the endpoint of the chain. I am sure that the EndPoint parameter could be computable - but for now I don't see any simple way to do that.

There is still need for the PathPart parameter - for the case when you have paths like "/book/$book_id/edition/$edition_id" and "/book/$book_id/edition", i.e. two paths that differ only in the number of parameters taken by the actions. Since you can have only one "edition" subroutine in the "Book" controller you need to alias a subroutine with a different name to act as if it has the name "edition" - this is what you can do with the PathPart attribute. I am tempted to also rename that one to Alias too - so that it would be more mnemonic.

Anyway the source can be downloaded from it's subdir in the Cat repository. Below is the POD for the Catalyst::Controller::PathArgs controller. And I am waiting for comments before I submit it to CPAN.


Catalyst::Controller::PathArgs - syntactic sugar for the Catalyst::DispatchType::Chained manpage.


  package MyApp::Controller::Root;
use base 'Catalyst::Controller::PathArgs';
__PACKAGE__->config->{namespace} = '';
  sub pathargsroot : PathArgs(1) {}

use Catalyst::Controller::PathArgs;
package TestApp::Controller::Pathargsroot;
  use base 'Catalyst::Controller::PathArgs';
  sub pathargsend : PathArgs(1) EndPoint { }


This Catalyst Controller base adds two new action attributes: PathArgs (taking one numerical argument) and EndPoint. This is entirely syntactic sugar over the the Catalyst::DispatchType::Chained manpage full machinery for paths like '/book/$book_id/edition/$edition_id/view' - with PathArgs you can chain the 'book', 'edition' and 'view' methods and declare how many parameters they take. EndPoint is needed to declare an ation as the end of the chain (in theory this should be computable - but for now I don't see any easy way to do that).

This package uses the Class::C3 manpage this means that you cannot use NEXT in classes based on it - but C3 looks like a good replacement for NEXT.

To declare that the book subroutine is the root chained action with one argument you need to declare it in the Root controller with:

  sub book : PathArgs(1) {

If we had a non chained path with /book/edition - the edition sub would be declared in the 'Book' controller - and this is the same case here - you just add PathArgs(1) to indicate that it is indeed chained and that it takes one parameter. So in the Book controller you add:

  sub edition : PathArgs(1) {

For the last action in the chain you need to add EndPoint. So in the Book::Edition controller you would need:

  sub view : PathArgs(0) EndPoint {

You can also mix PathArgs with PathPart (new in Catalyst 5.7007). For example if you wanted to have an action responding for the address ``/book/$book_id/edition'' you would need a subroutine called 'edition' in the Book controller, but there is already one routine called 'edition' in that controller. What you can do in that case is make a sub with a different name and declare that from the outside it's name should be really 'edition':

  sub edition_mascarade: PathPart('edition') PathArgs(0) EndPoint {

yeah - you need to add EndPoint there as well.

An example is included in the example directory of this distribution.

Internally PathArgs and EndPoint are converted to 'Chained(.)' and appriopriate CaptureArgs or Args attributes. For more sophisticated chaining you might need to use the Catalyst::DispatchType::Chained manpage directly.


This is the overriden method from Catalyst::Controller used here to compute the new attributes.




    Zbigniew Lukasiak


This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.


the Catalyst::DispatchType::Chained manpage

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