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Manual Reference Pages  -  DANCER::SESSION (3)

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Dancer::Session - session engine for the Dancer framework



version 1.3138


This module provides support for server-side sessions for the Dancer web framework. The session is accessible to the user via an abstraction layer implemented by the Dancer::Session class.



The session engine must be first enabled in the environment settings, this can be done like the following:

In the application code:

    # enabling the YAML-file-based session engine
    set session => YAML;

Or in config.yml or environments/$env.yml

    session: "YAML"

By default sessions are disabled, you must enable them before using it. If the session engine is disabled, any Dancer::Session call will throw an exception.

See Configuration in Dancer::Session::Abstract for more configuration options.

    Route Handlers

When enabled, the session engine can be used in a route handler with the keyword <B>sessionB>. This keyword allows you to store/retrieve values from the session by name.

Storing a value into the session:

    session foo => bar;

Retrieving that value later:

    my $foo = session foo;

You can either look for an existing item in the session storage or modify one. Here is a simple example of two route handlers that implement basic /login and /home actions using the session engine.

    post /login => sub {
        # look for params and authenticate the user
        # ...
        if ($user) {
            session user_id => $user->id;

    get /home => sub {
        # if a user is present in the session, let him go, otherwise redirect to
        # /login
        if (not session(user_id)) {
            redirect /login;

Of course, you probably don’t want to have to duplicate the code to check whether the user is logged in for each route handler; there’s an example in the Dancer::Cookbook showing how to use a before filter to check whether the user is logged in before all requests, and redirect to a login page if not.


Dancer has a modular session engine that makes implementing new session backends pretty easy. If you’d like to write your own, feel free to take a look at Dancer::Session::Abstract.

The following engines are supported out-of-the-box (shipped with the core Dancer distribution):
Dancer::Session::YAML A YAML file-based session backend, pretty convenient for development purposes, but maybe not the best for production needs.
Dancer::Session::Simple A very simple session backend, holding all session data in memory. This means that sessions are volatile, and no longer exist when the process exits. This module is likely to be most useful for testing purposes, and of little use for production.
Additionally, many more session engines are available from CPAN, including:
Dancer::Session::Memcached Session are stored in Memcached servers. This is good for production matters and is a good way to use a fast, distributed session storage. If you may be scaling up to add additional servers later, this will be a good choice.
Dancer::Session::Cookie This module implements a session engine for sessions stored entirely inside encrypted cookies (this engine doesn’t use a server-side storage).
Dancer::Session::Storable This backend stores sessions on disc using Storable, which offers solid performance and reliable serialization of various data structures.
Dancer::Session::MongoDB A backend to store sessions using MongoDB
Dancer::Session::KiokuDB A backend to store sessions using KiokuDB
Dancer::Session::PSGI Let Plack::Middleware::Session handle sessions; may be useful to share sessions between a Dancer app and other Plack-based apps.


Dancer::Session may depend on third-party modules, depending on the session engine used. See the session engine module for details.


This module has been written by Alexis Sukrieh. See the AUTHORS file that comes with this distribution for details.


This module is free software and is released under the same terms as Perl itself.


See Dancer for details about the complete framework.


Dancer Core Developers


This software is copyright (c) 2010 by Alexis Sukrieh.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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