package DBIx::Class::DeploymentHandler::HandlesVersioning; { $DBIx::Class::DeploymentHandler::HandlesVersioning::VERSION = '0.002204'; } use Moose::Role; # ABSTRACT: Interface for version methods requires 'next_version_set'; requires 'previous_version_set'; 1; # vim: ts=2 sw=2 expandtab __END__ =pod =head1 NAME DBIx::Class::DeploymentHandler::HandlesVersioning - Interface for version methods =head1 DESCRIPTION Typically a VersionHandler will take a C and yeild an iterator of L. Typically a call to a VersionHandler's L with a C of 1 and a C of 5 will iterate over something like the following: [1, 2] [2, 3] [3, 4] [4, 5] undef or maybe just [1, 5] undef Really how the L are arranged is up to the VersionHandler being used. In some cases users will not want versions to have inherent "previous versions," which is why the version set is an C. In those cases the user should opt to returning merely the version that the database is being upgraded to in each step. One idea that has been suggested to me has been to have a form of dependency management of the database "versions." In this case the versions are actually more like features that may or may not be applied. For example, one might start with version 1 and have a feature (version) C. Each feature might require that the database be upgraded to another version first. If one were to implement a system like this, here is how the VersionHandler's L might look. to_version = "users", db_version = 1 [3] [5] ["users"] undef So what just happened there is that C depends on version 5, which depends on version 3, which depends on version 1, which is already installed. To be clear, the reason we use single versions instead of version pairs is because there is no inherent order for this type of database upgraded. =head2 Downgrades For the typical case downgrades should be easy for users to perform and understand. That means that with the first two examples given above we can use the L iterator to yeild the following: db_version = 5, to_version=1 [5, 4] [4, 3] [3, 2] [2, 1] undef or maybe just [5, 1] undef Note that we do not swap the version number order. This allows us to remain consistent in our version set abstraction, since a version set really just describes a version change, and not necesarily a defined progression. =head1 VERSION SET A version set could be defined as: subtype 'Version', as 'Str'; subtype 'VersionSet', as 'ArrayRef[Str]'; A version set should uniquely identify a migration. =head1 KNOWN IMPLEMENTATIONS =over =item * L =item * L =item * L =back =head1 METHODS =head2 next_version_set print 'versions to install: '; while (my $vs = $dh->next_version_set) { print join q(, ), @{$vs} } print qq(\n); Return a L describing each version that needs to be installed to upgrade to C<< $dh->to_version >>. =head2 previous_version_set print 'versions to uninstall: '; while (my $vs = $dh->previous_version_set) { print join q(, ), @{$vs} } print qq(\n); Return a L describing each version that needs to be "installed" to downgrade to C<< $dh->to_version >>. =head1 AUTHOR Arthur Axel "fREW" Schmidt =head1 COPYRIGHT AND LICENSE This software is copyright (c) 2013 by Arthur Axel "fREW" Schmidt. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself. =cut