Data::Session - A persistent session manager

The Design of Data::Session, contrasted with CGI::Session

For background, read the docs (including the Changes files) and bug reports for both Apache::Session and CGI::Session.

The interface to Data::Session is not quite compatible with that of CGI::Session, hence the new namespace.

The purpose of Data::Session is to be a brand-new alternative to both Apache::Session and CGI::Session.

Aliases for Method Names

Aliases for method names are not supported.

In CGI::Session, methods etime() and expires() were aliased to expire(). This is not supported in Data::Session.

Data::Session does have an etime() method, "Method: etime()" in Data::Session, which is different.

In CGI::Session, method header() was aliased to http_header(). Only the latter method is supported in Data::Session. See "Method: cookie()" and "Method: http_header([@arg])".

In CGI::Session, id generators had a method generate_id() aliased to generate(). This is not supported in Data::Session.

In CGI::Session, method param_dataref() was aliased to dataref(). Neither of these methods is supported in Data::Session. If you want to access the session data, use my($hashref) = $session -> session.


This topic is sometimes used as a form of coercion, which is unacceptable, and sometimes leads to a crippled design.

So, by design, Data::Session is not exactly backwards-compatible with CGI::Session, but does retain it's major features:

o Specify the basic operating parameters with new(type => $string)

This determines the type of session object you wish to create.

Default: 'driver:File;id:MD5;serialize:DataDumper'.

And specifically, the format of that case-sensitive string is as expected. See "Specifying Session Options" in Data::Session for details.

o Retrieve the session id with the id() method
o Set and get parameters with the param() method
o Ensure session data is saved to disk with the flush() method

Call this just before your program exits.

In particular, as with CGI::Session, persistent environments stop your program exiting in the way you are used to. This matter is discussed in "Trouble with Exiting" in Data::Session.

CGI::Session::ExpireSessions is obsolete

Instead, consider using scripts/, which ships with Data::Session.

Code refs as database handles

Being able to supply a code ref as the value of the 'dbh' parameter to new() is supported.

This mechanism is used to delay creation of a database handle until it is actually needed, which means if it is not needed it is not created.

Class 'v' Object

Calling methods on the class is not supported. You must always create an object.

The reason for this is to ensure every method call, without exception, has access to the per-object data supplied by you, or by default, in the call to new().

The type of the Data::Session object

Controlling the capabilities of the Data::Session object is determined by the 'type' parameter passed in to new, as Data::Session -> new(type => $string).

A sample string looks like 'driver:BerkeleyDB;id:SHA1;serialize:DataDumper'.

Abbreviation of component key names ('driver', 'id', 'serialize') is not supported.

Such abbreviations were previously handled by Text::Abbrev. Now, these must be named in full.

The decision to force corresponding class names to lower case is not supported.

Nevertheless, lower-cased input will be accepted. Such input is converted to the case you expect.

This affects the names of various sub-classes. See "ID Generators", "Serialization Drivers" and "Storage Drivers".

For example, driver:pg is now driver:Pg, which actually means Data::Session::Driver::Pg, based on the class name DBD::Pg.


Exceptions are caught with Try::Tiny. Errors cause Data::Session to die.

The only exception to this is the call to new(), which can return undef. In that case, check $Data::Session::errstr.

Global Variables

Global variables are not supported. This includes:

o $CGI::Session::Driver::DBI::TABLE_NAME
o $CGI::Session::Driver::DBI::*::TABLE_NAME
o $CGI::Session::Driver::file::FileName
o $CGI::Session::IP_MATCH
o $CGI::Session::NAME

ID Generators

Id generator classes have been renamed:

o CGI::Session::ID::incr becomes Data::Session::ID::AutoIncrement
o CGI::Session::ID::md5 becomes Data::Session::ID::MD5
o CGI::Session::ID::sha becomes Data::Session::ID::SHA1
o CGI::Session::ID::sha256 becomes Data::Session::ID::SHA256
o CGI::Session::ID::sha512 becomes Data::Session::ID::SHA512
o CGI::Session::ID::static becomes Data::Session::ID::Static
o CGI::Session::ID::uuid becomes Data::Session::ID::UUID16 or UUID34 or UUID36 or UUD64


Data::Session::Serialize::JSON uses JSON, not JSON::Syck.

Managing Object Attributes

The light-weight Hash::FieldHash is used to manage object attributes.

So, neither Mouse nor Moose, nor any other such class helper, is used.

Method: cookie()

Forcing the query object to have a cookie method is not supported. You may now use a query class which does not provide a cookie method.

The logic of checking the cookie (if any) first (i.e. before checking for a form field of the same name) is supported.

See "Method: http_header([@arg])".

Method: http_header([@arg])

The [] indicate an optional parameter.

Returns a HTTP header. This means it does not print the header. You have to do that, when appropriate.

Forcing the document type to be 'text/html' when calling http_header() is not supported. You must pass in a document type to http_header(), as $session -> http_header('-type' => 'text/html'), or use the query object's default. Both CGI and CGI::Simple default to 'text/html'.

Data::Session handles the case where the query object does not have a cookie() method.

The @arg parameter, if any, is passed to the query object's header() method, after the cookie parameter, if any.

Method: load()

The new load() takes no parameters.

Method: new()

Excess versions of new() are not supported.

The new new() takes a hash of parameters.

This hash will include all options previously passed in in different parameters to new(), including $dsn, $query, $sid, \%dsn_args and \%session_params.

Name Changes

Class name changes are discussed in "ID Generators", "Serialization Drivers" and "Storage Drivers".

As discussed in "Method: new()" in Data::Session, these name changes are both the result of cleaning up all the options to new(), and because the option names are now also method names.

o DataColName becomes data_col_name

This is used in the call to new().

o DataSource becomes data_source

This is used in the call to new().

o generate_id becomes generate

This is used in various id generator classes, some of which provided generate as an alias.

o Handle becomes dbh

This is used in the call to new().

o IdColName becomes id_col_name

This is used in the call to new().

o IDFile becomes id_file

This is used in the call to new(), and in the '... id:AutoIncrement ...' id generator.

o IDIncr becomes id_step

This is used in the call to new(), and in the '... id:AutoIncrement ...' id generator.

o IDInit becomes id_base

This is used in the call to new(), and in the '... id:AutoIncrement ...' id generator.


Excess versions of param() will not be supported.

Use param($key => $value) to set and param($key) to get.

param() may be passed a hash, to set several key/value pairs in 1 call.


All POD has been re-written.

Race Conditions

The race handling code in CGI::Session::Driver::postgresql has been incorporated into other Data::Session::Driver::* drivers.

Serialization Drivers

Serializing classes have been renamed:

o CGI::Session::Serialize::default becomes Data::Session::Serialize::DataDumper
o CGI::Session::Serialize::freezethaw becomes Data::Session::Serialize::FreezeThaw
o CGI::Session::Serialize::json becomes Data::Session::Serialize::JSON

The latter will use JSON. In the past JSON::Syck was used.

o CGI::Session::Serialize::storable becomes Data::Session::Serialize::Storable
o CGI::Session::Serialize::yaml becomes Data::Session::Serialize::YAML

The latter uses YAML::Tiny. In the past either YAML::Syck or YAML was used.

Session ids will be mandatory

The ability to create a Perl object without a session id is not supported.

Every time a object of type Data::Session is created, it must have an id.

This id is either supplied by the caller, taken from the query object, or one is generated.

See "Specifying an Id" in Data::Session for details.

Session modification

CGI::Session tracks calls to param() to set a flag if the object is modified, so as to avoid writing the session to disk if nothing has been modified.

This includes checking if setting a param's value to the value it already has.

The behaviour is supported.

Session Parameters

CGI::Session had these internal object attributes (parameters) not available to the user:



o _DSN









Scalar (bitmap).



Data::Session has these internal object attributes (parameters):


Scalar: Last access time.


Scalar: Creation time.


Scalar: Expiry time.


Scalar: The id.


Hashref: Expiry times of parameters.

Data::Session stores user data internally in a hashref, and the module reserves keys starting with '_'.

Of course, it has a whole set of methods to manage state.

Session States

CGI::Session objects can be one of 6 states. Every attempt has been made to simplify this design.

Storage Drivers

Classes related to DBI/DBD will use DBD::* style names, to help beginners.

Hence (with special cases):

o CGI::Session::Driver::db_file becomes Data::Session::Driver::BerkeleyDB

The latter no longer uses DB_File.

o CGI::Session::Driver::file becomes Data::Session::Driver::File
o CGI::Session::Driver::memcached becomes Data::Session::Driver::Memcached
o CGI::Session::Driver::mysql becomes Data::Session::Driver::mysql
o CGI::Session::Driver::odbc becomes Data::Session::Driver::ODBC
o CGI::Session::Driver::oracle becomes Data::Session::Driver::Oracle
o CGI::Session::Driver::postgresql becomes Data::Session::Driver::Pg
o CGI::Session::Driver::sqlite becomes Data::Session::Driver::SQLite


All tests have been re-written.

The Version of Perl

Perl 5 code will be used.


Data::Session::Serialize::YAML uses YAML::Tiny, not YAML::Syck or YAML.


Data::Session was written by Ron Savage <> in 2010.

Home page:


Australian copyright (c) 2010, Ron Savage.

        All Programs of mine are 'OSI Certified Open Source Software';
        you can redistribute them and/or modify them under the terms of
        The Artistic License, a copy of which is available at: