Various fun things.

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

package DBIx::Class::Storage;

use strict;
use warnings;

use base qw/DBIx::Class/;

use Scalar::Util qw/weaken/;
use Carp::Clan qw/^DBIx::Class/;
use IO::File;
use DBIx::Class::Storage::TxnScopeGuard;

__PACKAGE__->mk_group_accessors('simple' => qw/debug debugobj schema/);
__PACKAGE__->mk_group_accessors('inherited' => 'cursor_class');

__PACKAGE__->cursor_class('DBIx::Class::Cursor');

sub cursor { shift->cursor_class(@_); }

package # Hide from PAUSE
    DBIx::Class::Storage::NESTED_ROLLBACK_EXCEPTION;

use overload '"' => sub {
  'DBIx::Class::Storage::NESTED_ROLLBACK_EXCEPTION'
};

sub new {
  my $class = shift;
  my $self = {};
  return bless $self, $class;
}

package DBIx::Class::Storage;

=head1 NAME

DBIx::Class::Storage - Generic Storage Handler

=head1 DESCRIPTION

A base implementation of common Storage methods.  For specific
information about L<DBI>-based storage, see L<DBIx::Class::Storage::DBI>.

=head1 METHODS

=head2 new

Arguments: $schema

Instantiates the Storage object.

=cut

sub new {
  my ($self, $schema) = @_;

  $self = ref $self if ref $self;

  my $new = {};
  bless $new, $self;

  $new->set_schema($schema);
  $new->debugobj(new DBIx::Class::Storage::Statistics());

  #my $fh;

  my $debug_env = $ENV{DBIX_CLASS_STORAGE_DBI_DEBUG}
                  || $ENV{DBIC_TRACE};

  $new->debug(1) if $debug_env;

  $new;
}

=head2 set_schema

Used to reset the schema class or object which owns this
storage object, such as during L<DBIx::Class::Schema/clone>.

=cut

sub set_schema {
  my ($self, $schema) = @_;
  $self->schema($schema);
  weaken($self->{schema}) if ref $self->{schema};
}

=head2 connected

Returns true if we have an open storage connection, false
if it is not (yet) open.

=cut

sub connected { die "Virtual method!" }

=head2 disconnect

Closes any open storage connection unconditionally.

=cut

sub disconnect { die "Virtual method!" }

=head2 ensure_connected

Initiate a connection to the storage if one isn't already open.

=cut

sub ensure_connected { die "Virtual method!" }

=head2 throw_exception

Throws an exception - croaks.

=cut

sub throw_exception {
  my $self = shift;

  $self->schema->throw_exception(@_) if $self->schema;
  croak @_;
}

=head2 txn_do

=over 4

=item Arguments: C<$coderef>, @coderef_args?

=item Return Value: The return value of $coderef

=back

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 @titles = qw/Night Day It/;

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

    return $author->books;
  };

  my $rs;
  eval {
    $rs = $schema->txn_do($coderef);
  };

  if ($@) {                                  # Transaction failed
    die "something terrible has happened!"   #
      if ($@ =~ /Rollback failed/);          # Rollback failed

    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</txn_commit>, and txn_do() can be
called in void, scalar and list context and it will behave as expected.

Please note that all of the code in your coderef, including non-DBIx::Class
code, is part of a transaction.  This transaction may fail out halfway, or
it may get partially double-executed (in the case that our DB connection
failed halfway through the transaction, in which case we reconnect and
restart the txn).  Therefore it is best that any side-effects in your coderef
are idempotent (that is, can be re-executed multiple times and get the
same result), and that you check up on your side-effects in the case of
transaction failure.

=cut

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

  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 txn_begin

Starts a transaction.

See the preferred L</txn_do> method, which allows for
an entire code block to be executed transactionally.

=cut

sub txn_begin { die "Virtual method!" }

=head2 txn_commit

Issues a commit of the current transaction.

=cut

sub txn_commit { die "Virtual method!" }

=head2 txn_rollback

Issues a rollback of the current transaction. A nested rollback will
throw a L<DBIx::Class::Storage::NESTED_ROLLBACK_EXCEPTION> exception,
which allows the rollback to propagate to the outermost transaction.

=cut

sub txn_rollback { die "Virtual method!" }

=head2 svp_begin

Arguments: $savepoint_name

Establishes a new savepoint of the specified name within the current
transaction.

=cut

sub svp_begin { die "Virtual method!" }

=head2 svp_release

Arguments: $savepoint_name

Destroy a savepoint, but keep the effects of the commands executed since
it's creation.

=cut

sub svp_release { die "Virtual method!" }

=head2 svp_rollback

Arguments: $savepoint_name

Rollback to the savepoint of the specified name.

=cut

sub svp_rollback { die "Virtual method!" }

=head2 svp_generate_name

Generates a name for the next savepoint.  Defaults to 'savepoint_$count',
where count is the number of current savepoints + 1.

=cut

sub svp_generate_name { die "Virtual method!" }

=for comment

=head2 txn_scope_guard

Return an object that does stuff.

=cut

sub txn_scope_guard {
  return DBIx::Class::Storage::TxnScopeGuard->new($_[0]);
}

=head2 sql_maker

Returns a C<sql_maker> object - normally an object of class
C<DBIC::SQL::Abstract>.

=cut

sub sql_maker { die "Virtual method!" }

=head2 debug

Causes trace information to be emitted on the C<debugobj> object.
(or C<STDERR> if C<debugobj> has not specifically been set).

This is the equivalent to setting L</DBIC_TRACE> in your
shell environment.

=head2 debugfh

Set or retrieve the filehandle used for trace/debug output.  This should be
an IO::Handle compatible ojbect (only the C<print> method is used.  Initially
set to be STDERR - although see information on the
L<DBIC_TRACE> environment variable.

=cut

sub debugfh {
    my $self = shift;

    if ($self->debugobj->can('debugfh')) {
        return $self->debugobj->debugfh(@_);
    }
}

=head2 debugobj

Sets or retrieves the object used for metric collection. Defaults to an instance
of L<DBIx::Class::Storage::Statistics> that is compatible with the original
method of using a coderef as a callback.  See the aforementioned Statistics
class for more information.

=head2 debugcb

Sets a callback to be executed each time a statement is run; takes a sub
reference.  Callback is executed as $sub->($op, $info) where $op is
SELECT/INSERT/UPDATE/DELETE and $info is what would normally be printed.

See L<debugobj> for a better way.

=cut

sub debugcb {
    my $self = shift;

    if ($self->debugobj->can('callback')) {
        return $self->debugobj->callback(@_);
    }
}

=head2 cursor_class

The cursor class for this Storage object.

=cut

=head2 deploy

Deploy the tables to storage (CREATE TABLE and friends in a SQL-based
Storage class). This would normally be called through
L<DBIx::Class::Schema/deploy>.

=cut

sub deploy { die "Virtual method!" }

=head2 connect_info

The arguments of C<connect_info> are always a single array reference,
and are Storage-handler specific.

This is normally accessed via L<DBIx::Class::Schema/connection>, which
encapsulates its argument list in an arrayref before calling
C<connect_info> here.

=cut

sub connect_info { die "Virtual method!" }

=head2 select

Handle a select statement.

=cut

sub select { die "Virtual method!" }

=head2 insert

Handle an insert statement.

=cut

sub insert { die "Virtual method!" }

=head2 update

Handle an update statement.

=cut

sub update { die "Virtual method!" }

=head2 delete

Handle a delete statement.

=cut

sub delete { die "Virtual method!" }

=head2 select_single

Performs a select, fetch and return of data - handles a single row
only.

=cut

sub select_single { die "Virtual method!" }

=head2 columns_info_for

Returns metadata for the given source's columns.  This
is *deprecated*, and will be removed before 1.0.  You should
be specifying the metadata yourself if you need it.

=cut

sub columns_info_for { die "Virtual method!" }

=head1 ENVIRONMENT VARIABLES

=head2 DBIC_TRACE

If C<DBIC_TRACE> is set then trace information
is produced (as when the L<debug> method is set).

If the value is of the form C<1=/path/name> then the trace output is
written to the file C</path/name>.

This environment variable is checked when the storage object is first
created (when you call connect on your schema).  So, run-time changes 
to this environment variable will not take effect unless you also 
re-connect on your schema.

=head2 DBIX_CLASS_STORAGE_DBI_DEBUG

Old name for DBIC_TRACE

=head1 SEE ALSO

L<DBIx::Class::Storage::DBI> - reference storage inplementation using SQL::Abstract and DBI.

=head1 AUTHORS

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

Andy Grundman <andy@hybridized.org>

=head1 LICENSE

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

=cut

1;