John Napiorkowski > Catalyst-ActionRole-QueryParameter > Catalyst::ActionRole::QueryParameter



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Catalyst::ActionRole::QueryParameter - Dispatch rules using query parameters


    package MyApp::Controller::Foo;

    use Moose;
    use MooseX::MethodAttributes;

    extends 'Catalyst::Controller:';

    ## Add the ActionRole to all the Controller's actions.  You can also
    ## selectively add the ActionRole with the :Does action attribute or in
    ## controller configuration.  See Catalyst::Controller::ActionRole for
    ## more information.

      action_roles => ['QueryParameter'],

    ## Match an incoming request matching "http://myhost/path?page=1"
    sub paged_results : Path('foo') QueryParam('page') { ... }

    ## Match an incoming request matching "http://myhost/path"
    sub no_paging : Path('foo') QueryParam('!page') { ... }

    ## Match a request using a type constraint

    use Types::Standard 'Int';
    sub an_int :Path('foo') QueryParam('page:Int') { ... }

    ## Match optionally (if the parameters exists it MUST pass the constraint
    ## BUT it is allowed to not exist

    use Types::Standard 'Int';
    sub an_int :Path('foo') QueryParam('?page:Int') { ... }

    ## Match with a default value if the query parameter does not exist'

    sub with_path :Path('foo') QueryParam('?page=1') { ... }


Let's you require conditions on request query parameters (as you would access via $ctx->request->query_parameters) as part of your dispatch matching. This ActionRole is not intended to be used for general HTML form and parameter processing or validation, for that purpose there are many other options (such as HTML::FormHandler, Data::Manager or HTML::FormFu.) What it can be useful for is when you want to delegate work to various Actions inside your Controller based on what the incoming query parameters say.

Generally speaking, it is not great development practice to abuse query parameters this way. However I find there is a limited and controlled subset of use cases where this feature is valuable. As a result, the features of this ActionRole are also limited to simple defined or undefined checking, and basic Perl relational operators.

You can specify multiple QueryParams per Action. If you do have more than one we will try to match Actions that match ALL the given QueryParam attributes.

There's a functioning Catalyst example application in the test directory for your review as well.


The value of the QueryParam attribute allows for condition matching based on query parameter definedness and via Perl relational operators. For example, you can match for a particular value or if a given value is greater than another. This can be useful when you want to perform a different Action when (for example) your user is on page 10 of a search, which might indicate they are not finding what they want and could use some additional help. I also sometimes find that I want special handling of the first page of a search result.

Although you can handle this with conditional logic inside your Action, I find the ability to declare what I want from an Action to be one of the more valuable aspects of Catalyst.

Here are some example QueryParam attributes and the queries they match:

    QueryParam('page')  ## 'page' must exist
    QueryParam('page=1') ## 'page' defaults to 1
    QueryParam('!page')  ## 'page' must NOT exist
    QueryParam('?page')  ## 'page' may optionally exist
    QueryParam('page:==1')  ## 'page' must equal numeric one
    QueryParam('page:>1')  ## 'page' must be great than one
    QueryParam('!page:>1')  ## 'page' must NOT be great than one
    QueryParam(page:Int) ## 'page' matches an Int constraint (see below)
    QueryParam('?page:Int')  ## 'page' may optionally exist, but if it does must be an Int

Since as I mentioned, it is generally not awesome web development practice to make excessive use of query parameters for mapping your action logic, I have limited the condition matching to basic Perl operators. The general pattern is as follows:


Which can be roughly translated as "A $parameter should match the $condition but we can tack a "!" to the front of the expression to reverse the match. If you don't specify a $condition, the default condition is definedness."

Please note your $parameter my define a simple default value using the '=' operator. This means your actual query parameter may not have a '=' in it. Patches to fix welcomed (it would probably be easy to provide some sort of escaping indicator). Default may be combined with conditions, but you can't combine a defualt AND an optional '?' indicator (will cause an error).

A $condition is basically a Perl relational operator followed by a value. Relation Operators we current support: ==,eq,>,<,!=,<=,>=,gt,ge,lt,le. In addition, we support the regular expression match operator =~. For documentation on Perl Relational Operators see: perldoc perlop. For documentation on Perl Regular Expressions see perldoc perlre.

A $condition may also be a Moose::Types or similar type constraint. See below for more.

NOTE For numeric comparisions we first check that the value 'looks_like_number' via Scalar::Util before doing the comparison. If it doesn't look like a number that is automatic fail.

NOTE The ? optional indicator is probably most useful when combined with a condition or/and a default.


To provide more flexibility and reuse in your parameter constraints, you may use types constraints as your constraint condition if you are using a recent build of Catalyst (at least version 5.90090 or greater). This allows you to use an imported type constraint, such as you might get from MooseX::Types or from Type::Tiny or Types::Standard. For example:

    package MyApp::Controller::Root;

    use base 'Catalyst::Controller';
    use Types::Standard 'Int';

    sub root :Chained(/) PathPart('') CaptureArgs(0) { }

      sub int :Chained(root) Args(0) QueryParam(page:Int) {
        my ($self, $c) = @_;

      action_roles => ['QueryParameter'],

This would require a URL with a 'page' query that is an Integer, for example, "https://localhost/int/100".

This feature uses the type constraint resolution features built into the new versions of Catalyst so it behaves the same way.


You may prefer to set your Query Parameter requirements via the Catalyst general application configuration, rather than in subroutine attributes. Doing so allows you to use different settings in different environments and it also allows you to use more extended values. Here's an example comparing both approaches

    ## subroutine attribute approach
    sub first_page : Path('foo') QueryParam('page:==1') { ... }

    ## configuration approach
      action => {
        first_page => { Path => 'foo', QueryParam => 'page:==1'},

Since the configuration approach allows richer use of Perl, you can replace the string version of the QueryParam value with the following:

    ## configuration approach, richer Perl data structure
      action => {
        first_page => { Path => 'foo', QueryParam => [['page','==','1']] },
        no_page_query => { Path => 'foo', QueryParam => [['!','page']] },

If you are using the configuration approach, this second option is preferred. Please note that since each attribute or configuration key can have an array of values, if you use the 'rich Perl data structure' approach in your configuration you will need to place the arrayref inside an arrayref as in the example above (that is not a typo!)


This document has been superceded by a new core documentation document. Please see Catalyst::RouteMatching.


Currently this only works for 'single' query parameters. For example:




Patches welcomed!


John Napiorkowski


Catalyst, Catalyst::Controller::ActionRole, Moose.


Copyright 2015, John Napiorkowski

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

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