Robert 'phaylon' Sedlacek > Catalyst-Controller-Constraints > Catalyst::Controller::Constraints



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Module Version: 0.10_02   Source  


Catalyst::Controller::Constraints - Constraint Signatures for Controller Actions


0.10_02 - Development Release. Production use not recommended yet.


  package MyApp::Controller::Foo;
  use base qw(Catalyst::Controller::Constraints);

      constraints => {

          #   allow only digits for type 'Integer'
          Integer => qr/^\d+$/,

          #   allow only word chars for type 'Word'
          Word    => sub { /^\w+$/ },

          #   validate user id and inflate to object
          User    => {

              #   check the user id
              check   => sub {
                  my ( $self, $c, $id ) = @_;
                  return $c->is_valid_user_id( $id );

              #   forward to this action if the validation failed
              on_fail => 'invalid_user',

              #   if value is valid, run it through this filter
              #   afterwards
              post_filter => sub {
                  my ( $self, $c, $id ) = @_;
                  $c->fetch_user_by_id( $id );

          #   inheritance
          HighInteger => {
              inherit_from => 'Integer',
              check        => sub { $_ > 22 },

          #   collapse multiple arguments
          MyDate => {

              #   take three integers and return one value
              takes => 3,
              gives => 1,

              #   inflate to a datetime object
              post_filter  => sub {
                  my ( $self, $c, $y, $m, $d ) = @_;
                      year => $y, month => $m, day => $d );

  #   add two integers, just throws exception on constraint failure
  sub add : Local Args(2) Constraints(Integer a, Integer b) {
      my ( $self, $c ) = @_;
      $c->res->body( $_{a} + $_{b} );

  #   puts the word into the stash, under the key 'foo'
  sub stashword : Local Args(1) Constraints( Word foo* ) { }

  #   user_obj ends as a user object in the stash
  sub view_user : Local Args(1) Constraints( User user_obj* ) { }
  sub invalid_user : Private {
      #   handle invalid userid



This controller base class for Catalyst enables you to apply constraints to your action arguments.


This describes how this controller base class is used. The first thing that has to be done is to use this instead of Catalyst::Controller as base class:

  package MyApp::Controller::Foo;
  use base qw(Catalyst::Controller::Constraints);

Defining Constraints

A constraint definition has no needed keys, though the check option is the most important. It can contain a code reference, a regular expression reference, or an array reference, containing a list of the former stated:

  MyNumA => { check => qr/^\d+$/ },
  MyNumB => { check => sub { $_ =~ qr/^\d+$/ } },
  MyNumC => { check => [qr/^\d+$/, sub { $_ > 23 }] },

If you just want to supply a check var, you can shortcut that:

  MyNumA => qr/^\d+$/,

As you can see, the arguments value is localized to $_ in your code reference to keep the definitions more readable. The @_ array contains the controller, the context, and then the constraints arguments, like an action working with the values.

There are some more options to specify, but let's walk them through step by step. There's a index of them at the bottom for quick referencing.

In every callback (pre_filter, check and post_filter) you are provided with the controller and context objects through $_{ctrl} and $_{ctx}. There's also has_param and param, but we'll be talking about them later.

There are three possible sources for constraint definitions:

Shipped constraints

See "Default Constraints" for information on which constraints are shipped and ready to use.

Constraints defined application wide

Constraints that are placed in your application config under the constraints key are available to the whole application. Any settings made under the name of a shipped constraint are merged together with the shipped config. The application constraints have, of course, priority over the shipped ones. The merging is especially useful to define app and per-controller actions for "Handling Validation Errors". Here is an example:

  package MyApp;
  use Catalyst/ -Debug /;

    constraints => {
      EvenNumber => {
        check => sub { $_ % 2 },
        on_fail => 'odd_number',
      Int => {
        on_fail => 'not_an_integer',
Constraints defined for one controller

These definitions look exactly as those for application wide constraints as they're introduced above. They differ in that they are only defined for the current controller, and have priority over shipped and application wide constraints.

For more control over the error message sent to the user, there is a function available named _(). A call to _( 'foobar' ) will throw a validation exception that can be handled (See "Handling Validation Errors"). The exception will have it's user_msg field set to the passed value.

Applying Constraints To Actions

The default constraint attribute name is Constraints, but you can change that with

  __PACKAGE__->config( constraint_attribute => 'Foo' );

in either your application or your controller. The constraints itself are just applied to actions through this attribute's parameter, as usual in Catalyst:

  sub foo : Local Constraint( Int bar, Int baz ) { ... }

You don't have to specify a constraint name. If you'd just do a

  sub foo : Local Constraint( Int bar, baz ) { ... }

then baz wouldn't be checked by any constraint. But you could still reference it by name. This can also be combined with another convenience function, autostashing:

  sub foo : Local Constraint( bar*, baz* ) { ... }

would when, for example, called with foo/23/17 set the values bar and baz in the stash to the corresponding values.

The original, unfiltered and unchanged values are passed to the action through @_, so this controller base class doesn't interfere with Catalyst's argument passing style at all. However, you can also access the values through the global %_ hash. In the above example, $_{bar} would be 23 and $_{baz} would be set to 17.

Handling Validation Errors

Through the on_fail option it's possible to handle a validation error of check. It's value can be a code reference, treated like an action, and a relative or absolute private action path. It's arguments will be The current controller, the context, and the exception object with the following fields:


This is the name of the constraint type, for example, Int.


The value that didn't pass the inspection.


Will be set to the value passed to _() if the exception was raised by this function.


The name of the argument that didn't pass the validation.

Here is a complete example:

  package MyApp::Controller::Foo;
  use base qw(Catalyst::Controller::Constraints);

    constraints => {
      MyInt => {
        check   => qr/^\d+$/,
        on_fail => 'invalid_input',

  sub add : Local Args(2) Constraints( MyInt a, MyInt b ) {
    $_[1]->response->body( $_{a} + $_{b} );

  sub invalid_input : Private {
    my ( $self, $c, $e ) = @_;
      sprintf 'Invalid format of %s for %s: %s',


Constraint Inheritance

Sometimes you don't want to override a constraint's behaviour, but rather add another layer above it. This is where constraint inheritance comes in:

  Word          => qr/^\w*$/,
  UserName      => { check => sub { length $_ > 5 }, inherit_from => 'Word' },

Using And Collapsing Multiple Arguments

Some arguments consist of more than one value, a date for example. You might want to use three values to create a datetime object. This is a simple example of this:

  MyDate => {
    takes => 3,
        gives => 1,
        post_filter => sub {
                my ( $self, $c, $y, $m, $d ) = @_;
                DateTime->new( year => $y, month => $m, day => $d );

Note the takes and gives values. The first indicates that this constraint takes the next three arguments, not just one. This has as consequence that pre_filter, post_filter, check and the exception objects value field contain a hashreference. Their return values are stored in an array reference, too. So a pre_filter that takes more than one value, but returns only one, results in an arrayref in the next calls (check and post_filter as value.

The gives value only affects how the value is passed to the dispatched action. A value of 1 (default is the value of takes, which has a default of 1) sets the value in %_ directly, rather than through an array reference.

Pre- And Post-Filters

This is pretty simple. These are callbacks that are called before and after check is running. They receive the value(s) in $_ and starting with index 2 in @_. Their return value is used as new value for the next calls.

Constraint Parameters

To prevent the need for many equal constraints, it is possible to pass a parameter to them. Usage examples would be Model constraints, that check for existance, permission and load the row from the database. A parameter can be passed to a constraint with [...] directly after its name:

  sub foo : Local Constraint( Model[Category] cat* ) { ... }

(This would also autostash the resulting object, due to *.)

Access to the parameter is provided through the global %_ hashes key param, read: $_{param}. To find out if a parameter was actually provided, you can check $_{has_param}.

Default Constraints

To set the on_fail handler for shipped constraints, override those parameter's option in your controller or application config.


Checks if the value consists only of digits, this means it's just a regular expression checking for ^\d+$.


Utilises Scalar::Util's looks_like_number function to check if the value, well, looks like a number.


Takes a regular expression parameter and validates the string against it. E.g.

  sub foo : Local Constraints( String[^\w+$] bar ) { }



Specifies how many arguments are used as input.


Specifies how many values are going to arrive at the action.


Callback, runs before check. Value is afterwards what was returned.


Validation check. Return true or false, or throw a validation exception with a user_msg through _().


Like pre_filter, but after check.



Overrides Catalyst::Controller's create_action to wrap the original one in a Catalyst::Controller::Constraints::Action proxy object.


Returns a constraint object by constraint name. If this type was already created, a cached version is returned.


Does the handling of the validation exceptions.



Robert 'phaylon' Sedlacek - <>


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.

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