KiokuDB::TypeMap::Entry::MOP(3)

NAME
KiokuDB::TypeMap::Entry::MOP - A KiokuDB::TypeMap entry for objects with a metaclass.

SYNOPSIS
    KiokuDB::TypeMap->new(
        entries => {
            'My::Class' => KiokuDB::TypeMap::Entry::MOP->new(
                intrinsic => 1,
            ),
        },
    );

DESCRIPTION
This typemap entry handles collapsing and expanding of Moose based objects.

It supports anonymous classes with runtime roles, the KiokuDB::Role::ID role.

Code for immutable classes is cached and performs several orders of magnitude better, so make use of "make_immutable" in Moose::Meta::Class.

ATTRIBUTES

intrinsic
    If true the object will be collapsed as part of its parent, without an ID.

check_class_versions
    If true (the default) then class versions will be checked on load and if there is a mismatch between the stored version number and the current version number, the version upgrade handler tables will be used to convert the out of date entry.

version_table
class_version_table
    Tables of handlers.

    See also KiokuDB::Role::Upgrade::Data and KiokuDB::Role::Upgrade::Handlers::Table for convenience roles that do not require a central table.

    The first is a global version table (useful when the typemap entry is only handling one class) and the second is a table of tables keyed by the class name.

    The tables are keyed by version number (as a string, "undef" and "" are considered the same), and the value can be either a code reference that processes the entry to bring it up to date, a hash reference of overridden fields, or a string denoting a version number that this version is equivalent to.

    Version numbers have no actual ordinal meaning, they are taken as simple string identifiers.

    If we had 3 versions, 1.0, 1.1 and 2.0, where 1.1 is a minor update to the class that requires no structural changes from 1.0, our table could be written like this:

        {
            '1.0' => '1.1', # upgrading the data from 1.0 to 1.1 is a noop
            '1.1' => sub {
                my ( $self, %args ) = @_;

                # manually convert the entry data
                return $entry->clone(
                    class_version => '2.0',
                    prev => $entry,
                    data => ...,
                ),
            },
        }

    When an object that was stored as version 1.0 is retrieved from the database, and the current definition of the class has $VERSION 2.0, table declares 1.0 is the same as 1.1, so we search for the handler for 1.1 and apply it.

    The resulting class has the version 2.0 which is the same as what we have now, so this object can be thawed.

    The callback is invoked with the following arguments:

    entry
        The entry to upgrade.

    from_version
        The key under which the handler was found (not necessarily the same as "$entry->class_version").

    meta
        The Class::MOP::Class of the entry's class.

    linker
        The KiokuDB::Linker instance that is inflating this object.

        Can be used to retrieve additional required objects (cycles are not a problem but be aware that the objects might not be usable yet at the time of the callback's invocation).

    When a hash is provided as a handler it'll be used to create an entry like this:

        $entry->derive(
            %$handler,
            data => {
                %{ $entry->data },
                %{ $handler->{data} || {} },
            },
        );

    The field "class_version" is required, and "data" must contain a hash:

        KiokuDB->connect(
            class_version_table => {
                Foo => {
                    "0.02" => {
                        class_version => "0.03", # upgrade 0.02 to 0.03
                        data => {
                            a_new_field => "default_value",
                        },
                    },
                },
            },
        );

write_upgrades
    If true, after applying version upgrade handlers, the updated entry will be written back to the database.

    Defaults to false but might default to true in future versions (unless the database is in readonly mode).