File Coverage

blib/lib/KiokuDB.pm

Criterion	Covered	Total	%
statement	228	291	78.3
branch	62	106	58.4
condition	12	22	54.5
subroutine	50	60	83.3
pod	20	28	71.4
total	372	507	73.3

#!/usr/bin/perl

package KiokuDB;
use Moose;

our $VERSION = "0.46_02";

use constant SERIAL_IDS => not not our $SERIAL_IDS;

use KiokuDB::Backend;
use KiokuDB::Collapser;
use KiokuDB::Linker;
use KiokuDB::LiveObjects;
use KiokuDB::TypeMap;
use KiokuDB::TypeMap::Shadow;
use KiokuDB::TypeMap::Resolver;
use KiokuDB::Stream::Objects;

use Hash::Util::FieldHash::Compat qw(idhash);
use Carp qw(croak);
use Try::Tiny;

use namespace::clean -except => [qw(meta SERIAL_IDS)];

# with qw(KiokuDB::Role::API); # moved lower

no warnings 'recursion';

our $REQUIRED_CMD_VERSION = "0.03";
sub cmd_is_up_to_date {
    require KiokuDB::Cmd;
    try { KiokuDB::Cmd->VERSION($REQUIRED_CMD_VERSION); 1 };
}


sub connect {
    my ( $class, $dsn, @args ) = @_;

    if ( -d $dsn || $dsn =~ /\.yml$/ ) {
        return $class->configure($dsn, @args);
    } else {
        require KiokuDB::Util;
        return $class->new( backend => KiokuDB::Util::dsn_to_backend($dsn, @args), @args );
    }
}

sub configure {
    my ( $class, $base, @args ) = @_;

    require Path::Class;
    $base = Path::Class::dir($base) unless blessed $base;

    require KiokuDB::Util;
    my $config = KiokuDB::Util::load_config($base);

    my $backend = KiokuDB::Util::config_to_backend( $config, base => $base, @args );

    # FIXME gin extractor, typemap, etc
    $class->new( %$config, @args, backend => $backend );
}

has typemap => (
    does => "KiokuDB::Role::TypeMap",
    is   => "ro",
);

has allow_class_builders => (
    isa => "Bool|HashRef",
    is  => "ro",
);

has [qw(allow_classes allow_bases)] => (
    isa => "ArrayRef[Str]",
    is  => "ro",
);

has merged_typemap => (
    does => "KiokuDB::Role::TypeMap",
    is   => "ro",
    lazy_build => 1,
);

sub _find_default_typemaps {
    my $self = shift;

    my $b = $self->backend;

    my @typemaps;
    if ( $b->can("default_typemap") ) {
        push @typemaps, $b->default_typemap;
    }


    if ( $b->can("serializer") and $b->serializer->can("default_typemap") ) {
        push @typemaps, $b->serializer->default_typemap;
    }

    return @typemaps;
}

sub _build_merged_typemap {
    my $self = shift;

    my @typemaps;

    if ( my $typemap = $self->typemap ) {
        push @typemaps, $typemap;
    }

    if ( my $classes = $self->allow_classes ) {
        require KiokuDB::TypeMap::Entry::Naive;

        push @typemaps, KiokuDB::TypeMap->new(
            entries => { map { $_ => KiokuDB::TypeMap::Entry::Naive->new } @$classes },
        );
    }

    if ( my $classes = $self->allow_bases ) {
        require KiokuDB::TypeMap::Entry::Naive;

        push @typemaps, KiokuDB::TypeMap->new(
            isa_entries => { map { $_ => KiokuDB::TypeMap::Entry::Naive->new } @$classes },
        );
    }

    if ( my $opts = $self->allow_class_builders ) {
        require KiokuDB::TypeMap::ClassBuilders;
        push @typemaps, KiokuDB::TypeMap::ClassBuilders->new( ref $opts ? %$opts : () );
    }

    push @typemaps, $self->_find_default_typemaps;

    if ( not @typemaps ) {
        return KiokuDB::TypeMap->new;
    } elsif ( @typemaps == 1 ) {
        return $typemaps[0];
    } else {
        return KiokuDB::TypeMap::Shadow->new( typemaps => \@typemaps );
    }
}

has check_class_versions => (
    isa => "Bool",
    is  => "ro",
    default => 0,
);

has class_version_table => (
    isa => "HashRef[HashRef[Str|CodeRef|HashRef]]",
    is  => "ro",
    default => sub { return {} },
);

has typemap_resolver => (
    isa => "KiokuDB::TypeMap::Resolver",
    is  => "ro",
    lazy_build => 1,
);

sub _build_typemap_resolver {
    my $self = shift;

    KiokuDB::TypeMap::Resolver->new(
        typemap        => $self->merged_typemap,
        fallback_entry => KiokuDB::TypeMap::Entry::MOP->new(
            class_version_table => $self->class_version_table,
            check_class_versions => $self->check_class_versions,
        ),
    );
}

has live_objects => (
    isa => "KiokuDB::LiveObjects",
    is  => "ro",
    coerce => 1,
    lazy => 1,
    builder => "_build_live_objects", # lazy_build => 1 sets clearer
    handles => {
        clear_live_objects => "clear",
        new_scope          => "new_scope",
        object_to_id       => "object_to_id",
        objects_to_ids     => "objects_to_ids",
        id_to_object       => "id_to_object",
        ids_to_objects     => "ids_to_objects",
    },
);

sub _build_live_objects { KiokuDB::LiveObjects->new }

has collapser => (
    isa => "KiokuDB::Collapser",
    is  => "ro",
    lazy_build => 1,
);

sub _build_collapser {
    my $self = shift;

    KiokuDB::Collapser->new(
        backend => $self->backend,
        live_objects => $self->live_objects,
        typemap_resolver => $self->typemap_resolver,
    );
}

has backend => (
    does => "KiokuDB::Backend",
    is   => "ro",
    required => 1,
    coerce   => 1,
);

has linker_queue => (
    isa => "Bool",
    is  => "ro",
    default => 1,
);

has linker => (
    isa => "KiokuDB::Linker",
    is  => "ro",
    lazy_build => 1,
);

sub _build_linker {
    my $self = shift;

    KiokuDB::Linker->new(
        backend => $self->backend,
        live_objects => $self->live_objects,
        typemap_resolver => $self->typemap_resolver,
        queue => $self->linker_queue,
    );
}

sub BUILD {
    my $self = shift;

    my $backend = $self->backend;

    $backend->register_handle($self) if $backend->can("register_handle");
}

with qw(KiokuDB::Role::API);

sub exists {
    my ( $self, @ids ) = @_;

    return unless @ids;

    my @exists = map { $_ ? 1 : '' } $self->backend->exists(@ids);
    return ( @ids == 1 ? $exists[0] : @exists );

    # FIXME fix for in_storage etc

    if ( @ids == 1 ) {
        my $id = $ids[0];

        if ( my $entry = $self->live_objects->id_to_entry($ids[0]) ) {
            return not $entry->deleted;
        }

        if ( my $entry = ($self->backend->exists($id))[0] ) { # backend returns a list
            if ( ref $entry ) {
                $self->live_objects->register_entry( $id => $entry, in_storage => 1 );
            }

            return 1;
        } else {
            return '';
        }
    } else {
        my ( %entries, %exists );

        @entries{@ids} = $self->live_objects->ids_to_entries(@ids);

        my @missing;

        foreach my $id ( @ids ) {
            if ( ref ( my $entry = $entries{$id} ) ) {
                $exists{$id} = not $entry->deleted;
            } else {
                push @missing, $id;
            }
        }

        if ( @missing ) {
            my @values = $self->backend->exists(@missing);

            if ( my @entries = grep { ref } @values ) {
                $self->live_objects->register_entry( $_->id => $_, in_storage => 1 ) for @entries;
            }

            @exists{@missing} = map { ref($_) ? 1 : $_ } @values;
        }

        return @ids == 1 ? $exists{$ids[0]} : @exists{@ids};
    }
}

sub lookup {
    my ( $self, @ids ) = @_;

    return unless @ids;

    my $linker = $self->linker;

    try {
        my @objects = $linker->get_or_load_objects(@ids);

        if ( @ids == 1 ) {
            return $objects[0];
        } else {
            return @objects;
        }
    } catch {
          return if blessed($_)
                and $_->isa("KiokuDB::Error::MissingObjects")
                and $_->missing_ids_are(@ids);

          die $_;
    };
}

sub search {
    my ( $self, @args ) = @_;

    if ( @args == 1 && ref $args[0] eq 'HASH' ) {
        return $self->simple_search(@args);
    } else {
        return $self->backend_search(@args);
    }
}

sub _load_entry_stream {
    my ( $self, $stream ) = @_;

    KiokuDB::Stream::Objects->new(
        directory => $self,
        entry_stream => $stream,
    );
}

sub simple_search {
    my ( $self, @args ) = @_;

    my $b = $self->backend;

    my $entries = $b->simple_search( @args, live_objects => $self->live_objects );

    my $objects = $self->_load_entry_stream($entries);

    return $b->simple_search_filter($objects, @args);
}

sub backend_search {
    my ( $self, @args ) = @_;

    my $b = $self->backend;

    my $entries = $b->search( @args, live_objects => $self->live_objects );

    my $objects = $self->_load_entry_stream($entries);

    return $b->search_filter($objects, @args);
}

sub root_set {
    my ( $self ) = @_;

    $self->_load_entry_stream( $self->backend->root_entries( live_objects => $self->live_objects ) );
}

sub all_objects {
    my ( $self ) = @_;

    $self->_load_entry_stream( $self->backend->all_entries( live_objects => $self->live_objects ) );
}

sub grep {
    my ( $self, $filter ) = @_;

    my $stream = $self->root_set;

    $stream->filter(sub { [ grep { $filter->($_) } @$_ ] });
}

sub scan {
    my ( $self, $filter ) = @_;

    my $stream = $self->root_set;

    while ( my $items = $stream->next ) {
        foreach my $item ( @$items ) {
            $item->$filter();
        }
    }
}

sub _parse_args {
    my ( $self, @args ) = @_;

    my ( %ids, @ret );

    while ( @args ) {
        my $next = shift @args;

        unless ( ref $next ) {
            my $obj = shift @args;

            $ids{$next} = $obj;

            push @ret, $obj;
        } else {
            push @ret, $next;
        }
    }

    return ( \%ids, @ret );
}

sub _register {
    my ( $self, @args ) = @_;

    my ( $ids, @objs ) = $self->_parse_args(@args);

    if ( scalar keys %$ids ) {
        $self->live_objects->insert(%$ids);
    }

    return @objs;
}

sub refresh {
    my ( $self, @objects ) = @_;

    return unless @objects;

    my $l = $self->live_objects;

    croak "Object not in storage"
        if grep { not $l->object_in_storage($_) } @objects;

    $self->linker->refresh_objects(@objects);

    if ( defined wantarray ) {
        if ( @objects == 1 ) {
           return $objects[0];
        } else {
           return @objects;
        }
    }
}

sub _store {
    my ( $self, $root, @args ) = @_;

    my @objects = $self->_register(@args);

    return unless @objects;

    $self->store_objects( root_set => $root, objects => \@objects );
}

sub store         { shift->_store( 1, @_ ) }
sub store_nonroot { shift->_store( 0, @_ ) }

sub _insert {
    my ( $self, $root, @args ) = @_;

    my @objects = $self->_register(@args);

    return unless @objects;

    my $l = $self->live_objects;

    # FIXME make optional?
    if ( my @in_storage = grep { $l->object_in_storage($_) } @objects ) {
        croak "Objects already in database: @in_storage";
    }

    $self->store_objects( root_set => $root, only_in_storage => 1, objects => \@objects );

    # return IDs only for unknown objects
    if ( defined wantarray ) {
        return $self->live_objects->objects_to_ids(@objects);
    }
}

sub insert         { shift->_insert( 1, @_ ) }
sub insert_nonroot { shift->_insert( 0, @_ ) }

sub update {
    my ( $self, @args ) = @_;

    my @objects = $self->_register(@args);

    my $l = $self->live_objects;

    croak "Object not in storage"
        if grep { not $l->object_in_storage($_) } @objects;

    $self->store_objects( shallow => 1, only_known => 1, objects => \@objects );
}

sub deep_update {
    my ( $self, @args ) = @_;

    my @objects = $self->_register(@args);

    my $l = $self->live_objects;

    croak "Object not in storage"
        if grep { not $l->object_in_storage($_) } @objects;

    $self->store_objects( only_known => 1, objects => \@objects );
}

sub _derive_entries {
    my ( $self, %args ) = @_;

    my @objects = @{ $args{objects} };

    my $l = $self->live_objects;

    my @entries = $l->objects_to_entries( @{ $args{objects} } );

    my $method = $args{method} || "derive";

    my $derive_args = $args{args} || [];

    my @args = ref($derive_args) eq 'HASH' ? %$derive_args : @$derive_args;

    $l->update_entries(map {
        my $obj = shift @objects;
        $obj => $_->$method( object => $obj, @args );
    } @entries);
}

sub set_root {
    my ( $self, @objects ) = @_;

    $self->_derive_entries( objects => \@objects, args => { root => 1 } );
}

sub unset_root {
    my ( $self, @objects ) = @_;

    $self->_derive_entries( objects => \@objects, args => { root => 0 } );
}

sub is_root {
    my ( $self, @objects ) = @_;

    my $l = $self->live_objects;

    my @is_root = map { $l->id_in_root_set($_) } $l->objects_to_ids(@objects);

    return @objects == 1 ? $is_root[0] : @is_root;
}

sub store_objects {
    my ( $self, %args ) = @_;

    my $objects = $args{objects};

    my ( $buffer, @ids ) = $self->collapser->collapse(%args);

    $buffer->imply_root(@ids) if $args{root_set};

    $buffer->commit($self->backend);

    if ( @$objects == 1 ) {
        return $ids[0];
    } else {
        return @ids;
    }
}

sub delete {
    my ( $self, @ids_or_objects ) = @_;

    return unless @ids_or_objects;

    my $l = $self->live_objects;

    my @ids = grep { not ref } @ids_or_objects;
    my @objects = grep { ref } @ids_or_objects;

    # FIXME requires 'deleted' flag or somesuch
    unless ( $l->keep_entries ) {
        push @ids, $l->objects_to_ids(@objects);
        @objects = ();
    }

    my @entries;

    for ( @objects ) {
        croak "Object not in storage" unless $l->object_in_storage($_);
    }

    push @entries, $l->objects_to_entries(@objects) if @objects;

    @entries = map { $_->deletion_entry } @entries;

    # FIXME ideally if ID is pointing at a live object we should use its entry
    #push @entries, $l->ids_to_entries(@ids) if @ids;
    my @ids_or_entries = ( @entries, @ids );

    if ( my @new_entries = grep { ref } $self->backend->delete(@ids_or_entries) ) {
        push @entries, @new_entries;
    }

    $l->remove(@ids_or_objects);
}

sub scoped_txn {
    my ( $self, $body, @args ) = @_;

    $self->txn_do(body => $body, scope => 1, @args);
}

sub txn_do {
    my ( $self, @args ) = @_;

    unshift @args, 'body' if @args % 2 == 1;

    my %args = @args;

    my $code = delete $args{body};

    my $s = $args{scope} && $self->new_scope;

    my $backend = $self->backend;

    if ( $backend->can("txn_do") ) {
        my $scope = $self->live_objects->new_txn;

        my $rollback = $args{rollback};
        $args{rollback} = sub { $scope && $scope->rollback; $rollback && $rollback->() };

        return $backend->txn_do( $code, %args );
    } else {
        return $code->();
    }
}

sub directory {
    my $self = shift;
    return $self;
}

__PACKAGE__->meta->make_immutable;

__PACKAGE__

__END__

=pod

=head1 NAME

KiokuDB - Object Graph storage engine

=head1 TUTORIAL

If you're new to L<KiokuDB> check out L<KiokuDB::Tutorial>.

=head1 SYNOPSIS

    use KiokuDB;

    # use a DSN
    my $d = KiokuDB->connect( $dsn, %args );

    # or manually instantiate a backend
    my $d = KiokuDB->new(
        backend => KiokuDB::Backend::Files->new(
            dir        => "/tmp/foo",
            serializer => "yaml",
        ),
    );


    # create a scope object
    my $s = $d->new_scope;


    # takes a snapshot of $some_object
    my $uuid = $d->store($some_object);

    # or with a custom ID:
    $d->store( $id => $some_object ); # $id can be any string


    # retrieve by ID
    my $some_object = $d->lookup($uuid);



    # some backends (like DBI) support simple searchs
    $d->search({ name => "foo" });


    # others use GIN queries (DBI supports both)
    $d->search($gin_query);

=head1 DESCRIPTION

L<KiokuDB> is a Moose based frontend to various data stores, somewhere in
between L<Tangram> and L<Pixie>.

Its purpose is to provide persistence for "regular" objects with as little
effort as possible, without sacrificing control over how persistence is
actually done, especially for harder to serialize objects.

L<KiokuDB> is also non-invasive: it does not use ties, C<AUTOLOAD>, proxy
objects, C<sv_magic> or any other type of trickery.

Many features important for proper Perl space semantics are supported,
including shared data, circular structures, weak references, tied structures,
etc.

L<KiokuDB> is meant to solve two related persistence problems:

=over 4

=item Transparent persistence

Store arbitrary objects without changing their class definitions or worrying
about schema details, and without needing to conform to the limitations of
a relational model.

=item Interoperability

Persisting arbitrary objects in a way that is compatible with existing
data/code (for example interoprating with another app using CouchDB with JSPON
semantics).

=back

=head1 FUNDAMENTAL CONCEPTS

In order to use any persistence framework it is important to understand what it
does and how it does it.

Systems like L<Tangram> or L<DBIx::Class> generally require explicit meta data
and use a schema, which makes them fairly predictable.

When using transparent systems like L<KiokuDB> or L<Pixie> it is more important
to understand what's going on behind the scenes in order to avoid surprises and
limitations.

An architectural overview is available on the website:
L<http://www.iinteractive.com/kiokudb/arch.html>

The process is explained here and in the various component documentation in
more detail.

=head2 Collapsing

When an object is stored using L<KiokuDB> it's collapsed into an
L<KiokDB::Entry|Entry>.

An entry is a simplified representation of the object, allowing the data to be
saved in formats as simple as JSON.

References to other objects are converted to symbolic references in the entry,
so objects can be saved independently of each other.

The entries are given to the L<KiokuDB::Backend|Backend> for actual storage.

Collapsing is explained in detail in L<KiokuDB::Collapser>. The way an entry is
created varies with the object's class.

=head2 Linking

When objects are loaded, entries are retrieved from the backend using their
UIDs.

When a UID is already loaded (in the live object set of a L<KiokuDB> instance,
see L<KiokuDB::LiveObjects>) the live object is used. This way references to
shared objects are shared in memory regardless of the order the objects were
stored or loaded.

This process is explained in detail in L<KiokuDB::Linker>.

=head1 ROOT SET MEMBERSHIP

Any object that is passed to C<store> or C<insert> directly is implicitly
considered a member of the root set.

This flag implies that the object is an identified resource and should not be
garbage collected with any of the proposed garbage collection schemes.

The root flag may be modified explicitly:

    $kiokudb->set_root(@objects); # or unset_root

    $kiokudb->update(@objects);

Lastly, root set membership may also be specified explicitly by the typemap.

A root set member must be explicitly removed using C<delete> or by
removing it from the root set. Only non-members of the root set will be
purged with any garbage collection scheme.

=head1 TRANSACTIONS

On supporting backends the C<txn_do> method will execute a block and commit the
transaction at its end.

Nesting of C<txn_do> blocks is always supported, though rolling back a nested
transaction may produce different results on different backends.

If the backend does not support transactions C<txn_do> simply executes the code
block normally.

=head1 CONCURRENCY

Most transactional backends are also concurrent.

L<KiokuDB::Backend::BDB> and L<KiokuDB::Backend::CouchDB> default to
serializable transaction isolation and do not suffer from deadlocks, but
serialization errors may occur, aborting the transaction (in which case the
transaction should be tried again).

L<KiokuDB::Backend::Files> provides good concurrency support but will only
detect deadlocks on platforms which return C<EDEADLK> from C<flock>.
L<Directory::Transactional> may provide alternative mechanisms in the future.

Concurrency support in L<KiokuDB::Backend::DBI> depends on the database. SQLite
defaults to serializable transaction isolation out of the box, wheras MySQL and
PostgreSQL default to read committed.

Depending on your application read committed isolation may be sufficient, but
due to the graph structure nature of the data repeatable reads or serializable
level isolation is highly reccomended. Read committed isolation generally works
well when each row in the database is more or less independent of others, and
various constraints ensure integrity. Unfortunately this is not the case with
the graph layout.

To enable stronger isolation guarantees see
L<KiokuDB::Backend::DBI/Transactions> for per-database pointers.

=head1 ATTRIBUTES

L<KiokuDB> uses a number of delegates which do the actual work.

Of these only C<backend> is required, the rest have default definitions.

Additional attributes that are not commonly used are listed in L</"INTERNAL
ATTRIBUTES">.

=over 4

=item backend

This attribute is required.

This must be an object that does L<KiokuDB::Backend>.

The backend handles storage and retrieval of entries.

=item typemap

This is an instance L<KiokuDB::TypeMap>.

The typemap contains entries which control how L<KiokuDB::Collapser> and
L<KiokuDB::Linker> handle different types of objects.

=item allow_classes

An array references of extra classes to allow.

Objects blessed into these classes will be collapsed using
L<KiokuDB::TypeMap::Entry:Naive>.

=item allow_bases

An array references of extra base classes to allow.

Objects derived from these classes will be collapsed using
L<KiokuDB::TypeMap::Entry:Naive>.

=item allow_class_builders

If true adds L<KiokuDB::TypeMap::ClassBuilders> to the merged typemap.

It's possible to provide a hash reference of options to give to
L<KiokuDB::TypeMap::ClassBuilders/new>.

=item check_class_versions

Controls whether or not the class versions of objects are checked on load.

Defaults to true.

=item class_version_table

A table of classes and versions that is passed to the default typemap entry for
Moose/Class::MOP objects.

When a class version has changed between the time that an object was stored and
the time it's being retrieved, the data must be converted.

See L<KiokuDB::TypeMap::Entry::MOP> for more details.

=back

=head1 METHODS

=over 4

=item connect $dsn, %args

DWIM wrapper for C<new>.

C<$dsn> represents some sort of backend (much like L<DBI> dsns map to DBDs).

An example DSN is:

    my $dir = KiokuDB->connect("bdb:dir=path/to/data/");

The backend moniker name is extracted by splitting on the colon. The rest of
the string is passed to C<new_from_dsn>, which is documented in more detail in
L<KiokuDB::Backend>.

Typically DSN arguments are separated by C<;>, with C<=> separating keys and
values. Arguments with no value are assumed to denote boolean truth (e.g.
C<jspon:dir=foo;pretty> means C<< dir => "foo", pretty => 1 >>). However, a
backend may override the default parsing, so this is not guaranteed.

Extra arguments are passed both to the backend constructor, and the C<KiokuDB>
constructor.

Note that if you need a typemap you still need to pass it in:

    KiokuDB->connect( $dsn, typemap => $typemap );

The DSN can also be a valid L<JSON> string taking one of the following forms:

    dsn => '["dbi:SQLite:foo",{"schema":"MyApp::DB"}]'

    dsn => '{"dsn":"dbi:SQLite:foo","schema":"MyApp::DB"}'

This allows more complicated arguments to be specified accurately, or arbitrary
options to be specified when the backend has nonstandard DSN parsing (for
instance L<KiokuDB::Backend::DBI> simply passes the string to L<DBI>, so this
is necessary in order to specify options on the command line).

=item configure $config_file, %args

TODO

=item new %args

Creates a new directory object.

See L</ATTRIBUTES>

=item new_scope

Creates a new object scope. Handled by C<live_objects>.

The object scope artificially bumps up the reference count of objects to ensure
that they live at least as long as the scope does.

This ensures that weak references aren't deleted prematurely, and the object
graph doesn't get corrupted without needing to create circular structures and
cleaning up leaks manually.

=item lookup @ids

Fetches the objects for the specified IDs from the live object set or from
storage.

=item store @objects

=item store %objects

=item store_nonroot @objects

=item store_nonroot %objects

Recursively collapses C<@objects> and inserts or updates the entries.

This performs a full update of every reachable object from C<@objects>,
snapshotting everything.

Strings found in the object list are assumed to be IDs for the following objects.

The C<nonroot> variant will not mark the objects as members of the root set
(therefore they will be subject to garbage collection).

=item update @objects

Performs a shallow update of @objects (referants are not updated).

It is an error to update an object not in the database.

=item deep_update @objects

Update @objects and all of the objects they reference. All references
objects must already be in the database.

=item insert @objects

=item insert %objects

=item insert_nonroot @objects

=item insert_nonroot %objects

Inserts objects to the database.

It is an error to insert objects that are already in the database, all elements
of C<@objects> must be new, but their referants don't have to be.

C<@objects> will be collapsed recursively, but the collapsing stops at known
objects, which will not be updated.

The C<nonroot> variant will not mark the objects as members of the root set
(therefore they will be subject to garbage collection).


=item delete @objects_or_ids

Deletes the specified objects from the store.

Note that this can cause lookup errors if the object you are deleting is
referred to by another object, because that link will be broken.

=item set_root @objects

=item unset_root @objects

Modify the C<root> flag on the associated entries.

C<update> must be called for the change to take effect.

=item txn_do $code, %args

=item txn_do %args

=item scoped_txn $code

Executes $code within the scope of a transaction.

This requires that the backend supports transactions
(L<KiokuDB::Backend::Role::TXN>).

If the backend does not support transactions, the code block will simply be
invoked.

Transactions may be nested.

If the C<scope> argument is true an implicit call to C<new_scope> will be made,
keeping the scope for the duration of the transaction.

The return value is propagated from the code block, with handling of
list/scalar/void context.

C<scoped_txn> is like C<txn_do> but sets C<scope> to true.

=item txn_begin

=item txn_commit

=item txn_rollback

These methods simply call the corresponding methods on the backend.

Like C<txn_do> these methods are no-ops if the backend does not support
transactions.

=item search \%proto

=item search @args

Searching requires a backend that supports querying.

The C<\%proto> form is currently unspecified but in the future should provide a
simple but consistent way of looking up objects by attributes.

The second form is backend specific querying, for instance
L<Search::GIN::Query> objects passed to L<KiokuDB::Backend::BDB::GIN> or
the generic GIN backend wrapper L<KiokuDB::GIN>.

Returns a L<Data::Stream::Bulk> of the results.

=item root_set

Returns a L<Data::Stream::Bulk> of all the root objects in the database.

=item all_objects

Returns a L<Data::Stream::Bulk> of all the objects in the database.

=item grep $filter

Returns a L<Data::Stream::Bulk> of the objects in C<root_set> filtered by
C<$filter>.

=item scan $callback

Iterates the root set calling C<$callback> for each object.

=item object_to_id

=item objects_to_ids

=item id_to_object

=item ids_to_objects

Delegates to L<KiokuDB::LiveObjects>

=item directory

Returns C<$self>.

This is used when setting up L<KiokuDB::Role::API> delegation chains. Calling
C<directory> on any level of delegator will always return the real L<KiokuDB>
instance no matter how deep.

=back

=head1 GLOBALS

=over 4

=item C<$SERIAL_IDS>

If set at compile time, the default UUID generation role will use serial IDs,
instead of UUIDs.

This is useful for testing, since the same IDs will be issued each run, but is
utterly broken in the face of concurrency.

=back

=head1 INTERNAL ATTRIBUTES

These attributes are documented for completeness and should typically not be
needed.

=over 4

=item collapser

L<KiokuDB::Collapser>

The collapser prepares objects for storage, by creating L<KiokDB::Entry>
objects to pass to the backend.

=item linker

L<KiokuDB::Linker>

The linker links entries into functioning instances, loading necessary
dependencies from the backend.

=item live_objects

L<KiokuDB::LiveObjects>

The live object set keeps track of objects and entries for the linker and the
resolver.

It also creates scope objects that help ensure objects don't garbage collect
too early (L<KiokuDB::LiveObjects/new_scope>, L<KiokuDB::LiveObjects::Scope>),
and transaction scope objects used by C<txn_do>
(L<KiokuDB::LiveObjects::TXNScope>).

=item typemap_resolver

An instance of L<KiokuDB::TypeMap::Resolver>. Handles actual lookup and
compilation of typemap entries, using the user typemap.

=back

=head1 SEE ALSO

=head2 Prior Art on the CPAN

=over 4

=item L<Pixie>

=item L<DBM::Deep>

=item L<OOPS>

=item L<Tangram>

=item L<DBIx::Class>

Polymorphic retrieval is possible with L<DBIx::Class::DynamicSubclass>

=item L<Fey::ORM>

=item L<MooseX::Storage>

=back

=head1 VERSION CONTROL

KiokuDB is maintained using Git. Information about the repository is available
on L<http://www.iinteractive.com/kiokudb/>

=head1 AUTHOR

Yuval Kogman E<lt>[e-mail]<gt>

=head1 COPYRIGHT

    Copyright (c) 2008, 2009 Yuval Kogman, Infinity Interactive. All
    rights reserved This program is free software; you can redistribute
    it and/or modify it under the same terms as Perl itself.

=cut