expanded/clarified documentation

[dbsrgits/DBIx-Class.git] / lib / DBIx / Class / Schema.pm

package DBIx::Class::Schema;

use strict;
use warnings;

use Carp::Clan qw/^DBIx::Class/;

use base qw/DBIx::Class/;

__PACKAGE__->mk_classdata('class_mappings' => {});
__PACKAGE__->mk_classdata('source_registrations' => {});
__PACKAGE__->mk_classdata('storage_type' => '::DBI');
__PACKAGE__->mk_classdata('storage');

=head1 NAME

DBIx::Class::Schema - composable schemas

=head1 SYNOPSIS

  package Library::Schema;
  use base qw/DBIx::Class::Schema/;
  
  # load Library::Schema::CD, Library::Schema::Book, Library::Schema::DVD
  __PACKAGE__->load_classes(qw/CD Book DVD/);

  package Library::Schema::CD;
  use base qw/DBIx::Class/;
  __PACKAGE__->load_components(qw/PK::Auto Core/); # for example
  __PACKAGE__->table('cd');

  # Elsewhere in your code:
  my $schema1 = Library::Schema->connect(
    $dsn,
    $user,
    $password,
    { AutoCommit => 0 },
  );
  
  my $schema2 = Library::Schema->connect($coderef_returning_dbh);

  # fetch objects using Library::Schema::DVD
  my $resultset = $schema1->resultset('DVD')->search( ... );
  my @dvd_objects = $schema2->resultset('DVD')->search( ... );

=head1 DESCRIPTION

Creates database classes based on a schema. This is the recommended way to
use L<DBIx::Class> and allows you to use more than one concurrent connection
with your classes.

NB: If you're used to L<Class::DBI> it's worth reading the L</SYNOPSIS>
carefully as DBIx::Class does things a little differently. Note in
particular which module inherits off which.

=head1 METHODS

=head2 register_class

=head3 Arguments: ($moniker, $component_class)

Registers a class which isa L<DBIx::Class::ResultSourceProxy>. Equivalent to
calling

  $schema->register_source($moniker, $component_class->result_source_instance);

=cut

sub register_class {
  my ($self, $moniker, $to_register) = @_;
  $self->register_source($moniker => $to_register->result_source_instance);
}

=head2 register_source

=head3 Arguments: ($moniker, $result_source)

Registers the L<DBIx::Class::ResultSource> in the schema with the given
moniker.

=cut

sub register_source {
  my ($self, $moniker, $source) = @_;
  my %reg = %{$self->source_registrations};
  $reg{$moniker} = $source;
  $self->source_registrations(\%reg);
  $source->schema($self);
  if ($source->result_class) {
    my %map = %{$self->class_mappings};
    $map{$source->result_class} = $moniker;
    $self->class_mappings(\%map);
  }
} 

=head2 class

=head3 Arguments: ($moniker)

=head3 Returns: $classname

Retrieves the result class name for the given moniker.

e.g.,

  my $class = $schema->class('CD');

=cut

sub class {
  my ($self, $moniker) = @_;
  return $self->source($moniker)->result_class;
}

=head2 source

=head3 Arguments: ($moniker)

=head3 Returns: $result_source

  my $source = $schema->source('Book');

Returns the L<DBIx::Class::ResultSource> object for the registered moniker.

=cut

sub source {
  my ($self, $moniker) = @_;
  my $sreg = $self->source_registrations;
  return $sreg->{$moniker} if exists $sreg->{$moniker};

  # if we got here, they probably passed a full class name
  my $mapped = $self->class_mappings->{$moniker};
  $self->throw_exception("Can't find source for ${moniker}")
    unless $mapped && exists $sreg->{$mapped};
  return $sreg->{$mapped};
}

=head2 sources

=head3 Returns: @source_monikers

Returns the source monikers of all source registrations on this schema.

e.g.,

  my @source_monikers = $schema->sources;

=cut

sub sources { return keys %{shift->source_registrations}; }

=head2 resultset

=head3 Arguments: ($moniker)

=head3 Returns: $result_set

  my $rs = $schema->resultset('DVD');

Returns the L<DBIx::Class::ResultSet> object for the registered moniker.

=cut

sub resultset {
  my ($self, $moniker) = @_;
  return $self->source($moniker)->resultset;
}

=head2 load_classes

=head3 Arguments: @classes?, { $namespace => [ @classes ] }+

With no arguments, this method uses L<Module::Find> to find all classes under
the schema's namespace. Otherwise, this method loads the classes you specify
(using L<use>), and registers them (using L</"register_class">).

It is possible to comment out classes with a leading '#', but note that perl
will think it's a mistake (trying to use a comment in a qw list) so you'll
need to add "no warnings 'qw';" before your load_classes call.

e.g.,

  My::Schema->load_classes(); # loads My::Schema::CD, My::Schema::Artist,
			      # etc. (anything under the My::Schema namespace)

  # loads My::Schema::CD, My::Schema::Artist, Other::Namespace::Producer but
  # not Other::Namespace::LinerNotes nor My::Schema::Track
  My::Schema->load_classes(qw/ CD Artist #Track /, {
    Other::Namespace => [qw/ Producer #LinerNotes /],
  });

=cut

sub load_classes {
  my ($class, @params) = @_;
  
  my %comps_for;
  
  if (@params) {
    foreach my $param (@params) {
      if (ref $param eq 'ARRAY') {
        # filter out commented entries
        my @modules = grep { $_ !~ /^#/ } @$param;
        
        push (@{$comps_for{$class}}, @modules);
      }
      elsif (ref $param eq 'HASH') {
        # more than one namespace possible
        for my $comp ( keys %$param ) {
          # filter out commented entries
          my @modules = grep { $_ !~ /^#/ } @{$param->{$comp}};

          push (@{$comps_for{$comp}}, @modules);
        }
      }
      else {
        # filter out commented entries
        push (@{$comps_for{$class}}, $param) if $param !~ /^#/;
      }
    }
  } else {
    eval "require Module::Find;";
    $class->throw_exception(
      "No arguments to load_classes and couldn't load Module::Find ($@)"
    ) if $@;
    my @comp = map { substr $_, length "${class}::"  }
                 Module::Find::findallmod($class);
    $comps_for{$class} = \@comp;
  }

  my @to_register;
  {
    no warnings qw/redefine/;
    local *Class::C3::reinitialize = sub { };
    foreach my $prefix (keys %comps_for) {
      foreach my $comp (@{$comps_for{$prefix}||[]}) {
        my $comp_class = "${prefix}::${comp}";
        eval "use $comp_class"; # If it fails, assume the user fixed it
        if ($@) {
	  $comp_class =~ s/::/\//g;
          die $@ unless $@ =~ /Can't locate.+$comp_class\.pm\sin\s\@INC/;
	  warn $@ if $@;
        }
        push(@to_register, [ $comp, $comp_class ]);
      }
    }
  }
  Class::C3->reinitialize;

  foreach my $to (@to_register) {
    $class->register_class(@$to);
    #  if $class->can('result_source_instance');
  }
}

=head2 compose_connection

=head3 Arguments: ($target_namespace, @db_info)

=head3 Returns: $new_schema

Calls L<DBIx::Class::schema/"compose_namespace"> to the target namespace,
calls L<DBIx::Class::Schema/connection>(@db_info) on the new schema, then
injects the L<DBix::Class::ResultSetProxy> component and a resultset_instance
classdata entry on all the new classes in order to support
$target_namespaces::$class->search(...) method calls.

This is primarily useful when you have a specific need for class method access
to a connection. In normal usage it is preferred to call
L<DBIx::Class::Schema/connect> and use the resulting schema object to operate
on L<DBIx::Class::ResultSet> objects with L<DBIx::Class::Schema/resultset> for
more information.

=cut

sub compose_connection {
  my ($self, $target, @info) = @_;
  my $base = 'DBIx::Class::ResultSetProxy';
  eval "require ${base};";
  $self->throw_exception
    ("No arguments to load_classes and couldn't load ${base} ($@)")
      if $@;

  if ($self eq $target) {
    # Pathological case, largely caused by the docs on early C::M::DBIC::Plain
    foreach my $moniker ($self->sources) {
      my $source = $self->source($moniker);
      my $class = $source->result_class;
      $self->inject_base($class, $base);
      $class->mk_classdata(resultset_instance => $source->resultset);
      $class->mk_classdata(class_resolver => $self);
    }
    $self->connection(@info);
    return $self;
  }

  my $schema = $self->compose_namespace($target, $base);
  {
    no strict 'refs';
    *{"${target}::schema"} = sub { $schema };
  }

  $schema->connection(@info);
  foreach my $moniker ($schema->sources) {
    my $source = $schema->source($moniker);
    my $class = $source->result_class;
    #warn "$moniker $class $source ".$source->storage;
    $class->mk_classdata(result_source_instance => $source);
    $class->mk_classdata(resultset_instance => $source->resultset);
    $class->mk_classdata(class_resolver => $schema);
  }
  return $schema;
}

=head2 compose_namespace

=head3 Arguments: $target_namespace, $additional_base_class?

=head3 Returns: $new_schema

For each L<DBIx::Class::ResultSource> in the schema, this method creates a
class in the target namespace (e.g. $target_namespace::CD,
$target_namespace::Artist) that inherits from the corresponding classes
attached to the current schema.

It also attaches a corresponding L<DBIx::Class::ResultSource> object to the
new $schema object. If C<$additional_base_class> is given, the new composed
classes will inherit from first the corresponding classe from the current
schema then the base class.

e.g. (for a schema with My::Schema::CD and My::Schema::Artist classes),

  $schema->compose_namespace('My::DB', 'Base::Class');
  print join (', ', @My::DB::CD::ISA) . "\n";
  print join (', ', @My::DB::Artist::ISA) ."\n";

Will produce the output

  My::Schema::CD, Base::Class
  My::Schema::Artist, Base::Class

=cut

sub compose_namespace {
  my ($self, $target, $base) = @_;
  my %reg = %{ $self->source_registrations };
  my %target;
  my %map;
  my $schema = $self->clone;
  {
    no warnings qw/redefine/;
    local *Class::C3::reinitialize = sub { };
    foreach my $moniker ($schema->sources) {
      my $source = $schema->source($moniker);
      my $target_class = "${target}::${moniker}";
      $self->inject_base(
        $target_class => $source->result_class, ($base ? $base : ())
      );
      $source->result_class($target_class);
    }
  }
  Class::C3->reinitialize();
  {
    no strict 'refs';
    foreach my $meth (qw/class source resultset/) {
      *{"${target}::${meth}"} =
        sub { shift->schema->$meth(@_) };
    }
  }
  return $schema;
}

=head2 setup_connection_class

=head3 Arguments: ($target, @info)

Sets up a database connection class to inject between the schema and the
subclasses that the schema creates.

=cut

sub setup_connection_class {
  my ($class, $target, @info) = @_;
  $class->inject_base($target => 'DBIx::Class::DB');
  #$target->load_components('DB');
  $target->connection(@info);
}

=head2 connection

=head3 Arguments: (@args)

=head3 Returns: $new_schema

Instantiates a new Storage object of type
L<DBIx::Class::Schema/"storage_type"> and passes the arguments to
$storage->connect_info. Sets the connection in-place on the schema. See
L<DBIx::Class::Storage::DBI/"connect_info"> for more information.

=cut

sub connection {
  my ($self, @info) = @_;
  return $self if !@info && $self->storage;
  my $storage_class = $self->storage_type;
  $storage_class = 'DBIx::Class::Storage'.$storage_class
    if $storage_class =~ m/^::/;
  eval "require ${storage_class};";
  $self->throw_exception(
    "No arguments to load_classes and couldn't load ${storage_class} ($@)"
  ) if $@;
  my $storage = $storage_class->new;
  $storage->connect_info(\@info);
  $self->storage($storage);
  return $self;
}

=head2 connect

=head3 Arguments: (@info)

=head3 Returns: $new_schema

This is a convenience method. It is equivalent to calling
$schema->clone->connection(@info). See L</connection> and L</clone> for more
information.

=cut

sub connect { shift->clone->connection(@_) }

=head2 txn_begin

Begins a transaction (does nothing if AutoCommit is off). Equivalent to
calling $schema->storage->txn_begin. See
L<DBIx::Class::Storage::DBI/"txn_begin"> for more information.

=cut

sub txn_begin { shift->storage->txn_begin }

=head2 txn_commit

Commits the current transaction. Equivalent to calling
$schema->storage->txn_commit. See L<DBIx::Class::Storage::DBI/"txn_commit">
for more information.

=cut

sub txn_commit { shift->storage->txn_commit }

=head2 txn_rollback

Rolls back the current transaction. Equivalent to calling
$schema->storage->txn_rollback. See
L<DBIx::Class::Storage::DBI/"txn_rollback"> for more information.

=cut

sub txn_rollback { shift->storage->txn_rollback }

=head2 txn_do

=head3 Arguments: (C<$coderef>, @coderef_args?)

=head3 Returns: (C<$return_value> | C<@return_values> | C<undef>) for scalar,
list and void contexts, respectively

Executes C<$coderef> with (optional) arguments C<@coderef_args> atomically,
returning its result (if any). If an exception is caught, a rollback is issued
and the exception is rethrown. If the rollback fails, (i.e. throws an
exception) an exception is thrown that includes a "Rollback failed" message.

For example,

  my $author_rs = $schema->resultset('Author')->find(1);

  my $coderef = sub {
    my ($author, @titles) = @_;

    # If any one of these fails, the entire transaction fails
    $author->create_related('books', {
      title => $_
    }) foreach (@titles);

    return $author->books;
  };

  my $rs;
  eval {
    $rs = $schema->txn_do($coderef, $author_rs, qw/Night Day It/);
  };

  if ($@) {
    my $error = $@;
    if ($error =~ /Rollback failed/) {
      die "something terrible has happened!";
    } else {
      deal_with_failed_transaction();
    }
  }

In a nested transaction (calling txn_do() from within a txn_do() coderef) only
the outermost transaction will issue a L<DBIx::Class::Schema/"txn_commit"> on
the Schema's storage, and txn_do() can be called in void, scalar and list
context and it will behave as expected.

=cut

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

  ref $self or $self->throw_exception
    ('Cannot execute txn_do as a class method');
  ref $coderef eq 'CODE' or $self->throw_exception
    ('$coderef must be a CODE reference');

  my (@return_values, $return_value);

  $self->txn_begin; # If this throws an exception, no rollback is needed

  my $wantarray = wantarray; # Need to save this since the context
			     # inside the eval{} block is independent
			     # of the context that called txn_do()
  eval {

    # Need to differentiate between scalar/list context to allow for
    # returning a list in scalar context to get the size of the list
    if ($wantarray) {
      # list context
      @return_values = $coderef->(@args);
    } elsif (defined $wantarray) {
      # scalar context
      $return_value = $coderef->(@args);
    } else {
      # void context
      $coderef->(@args);
    }
    $self->txn_commit;
  };

  if ($@) {
    my $error = $@;

    eval {
      $self->txn_rollback;
    };

    if ($@) {
      my $rollback_error = $@;
      my $exception_class = "DBIx::Class::Storage::NESTED_ROLLBACK_EXCEPTION";
      $self->throw_exception($error)  # propagate nested rollback
	if $rollback_error =~ /$exception_class/;

      $self->throw_exception(
        "Transaction aborted: $error. Rollback failed: ${rollback_error}"
      );
    } else {
      $self->throw_exception($error); # txn failed but rollback succeeded
    }
  }

  return $wantarray ? @return_values : $return_value;
}

=head2 clone

=head3 Returns: $new_schema

Clones the schema and its associated result_source objects and returns the
copy.

=cut

sub clone {
  my ($self) = @_;
  my $clone = bless({ (ref $self ? %$self : ()) }, ref $self || $self);
  foreach my $moniker ($self->sources) {
    my $source = $self->source($moniker);
    my $new = $source->new($source);
    $clone->register_source($moniker => $new);
  }
  return $clone;
}

=head2 populate

=head3 Arguments: ($moniker, \@data);

Populates the source registered with the given moniker with the supplied data.
@data should be a list of listrefs -- the first containing column names, the
second matching values.

i.e.,

  $schema->populate('Artist', [
    [ qw/artistid name/ ],
    [ 1, 'Popular Band' ],
    [ 2, 'Indie Band' ],
    ...
  ]);

=cut

sub populate {
  my ($self, $name, $data) = @_;
  my $rs = $self->resultset($name);
  my @names = @{shift(@$data)};
  my @created;
  foreach my $item (@$data) {
    my %create;
    @create{@names} = @$item;
    push(@created, $rs->create(\%create));
  }
  return @created;
}

=head2 throw_exception

=over 4 

=item Arguments: ($message)

=back

Throws an exception. Defaults to using L<Carp::Clan> to report errors from
user's perspective.

=cut

sub throw_exception {
  my ($self) = shift;
  croak @_;
}

=head2 deploy (EXPERIMENTAL)

=over 4

=item Arguments: ($sqlt_args)

=back

Attempts to deploy the schema to the current storage using L<SQL::Translator>.

Note that this feature is currently EXPERIMENTAL and may not work correctly
across all databases, or fully handle complex relationships.

=cut

sub deploy {
  my ($self, $sqltargs) = @_;
  $self->throw_exception("Can't deploy without storage") unless $self->storage;
  $self->storage->deploy($self, undef, $sqltargs);
}

1;

=head1 AUTHORS

Matt S. Trout <mst@shadowcatsystems.co.uk>

=head1 LICENSE

You may distribute this code under the same terms as Perl itself.

=cut