[Dbix-class] table-per-subclass - how it works?

[Hailin Hu]

I have no idea about "standard" solution, but another idea for reference :)

Package Base;
use base 'DBIx::Class::Core';

# parents' name should be a defined has_one or belong_to relationship
has 'parents' => (
  is => 'rw',
  isa => 'ArrayRef[Str]',
  builder => _build_parents,
);

sub inflate_result {
  my $self = shift;
  my $ret = $self->next::method( @_ );
  foreach my $relationship ( @{ $ret->parents } ) {
    my $parent = $ret->$relationship;
    my @columns = ... # @columns_in_$parent - @column_in_$ret
    foreach my $column ( @columns ) {
      # stolen from DBIx::Class's source
      no strict 'refs';
      no warnings 'redefine';
      my $method = join '::', ref $ret, $column;
      *$method = Sub::Name::subname( $method, sub {
        return $ret->$parent->$column;
      });
    }
  }
}
...

package Target;
extends 'Base';
...

package Host;
extends 'Base';
__PACKAGE__->belong_to('target' => 'Target', 'target_id');
sub _build_parents {[qw/target/]}
...

so just declare the attribute 'parents' in subclass is ok.
the task is not typical for me, but interesting.

On Fri, Jun 15, 2012 at 3:59 PM, Alex Erzin <eaa-home at yandex.ru> wrote:
> Yes, in some cases you are right, but you are saying about "long inheritance chains" and other cases where inheritance is not enought flexible,
> but i say about just one case in one place where inheritance is preferred for me, and i try to find solution _how_ to implement inheritance, but not about _why_not_ :)
>
>
> 15.06.2012, 10:43, "Ben Tilly" <btilly at gmail.com>:
>> The benefits of OOP are mostly in information hiding.
>>
>> If you're creating a bunch of long inheritance chains, you're probably
>> doing OOP poorly.  Composition is preferred.  And maps *much* more
>> naturally onto a relational database.
>>
>> On Thu, Jun 14, 2012 at 11:37 PM, Alex Erzin <eaa-home at yandex.ru> wrote:
>>
>>>  Hm... it really works, but where are benefits of OOP? ;)
>>>  There is no inheritance at all, and to access parent's properties I should call parent directly, so inheritance just replaced with incapsulation, and it's no one what i try to find.
>>>
>>>  Some years ago we have implemented inheritance in ORM in some commercial project in Perl, later I have swithed to java and have found Hibernate it really cool with ORM.
>>>  But now I have returned to Perl and I think that DBIx::Class can help me with ORM, but right now i'm confused that cannot find "standard" solution for typical task.
>>>
>>>  15.06.2012, 10:25, "Hailin Hu" <i at h2l.name>:
>>>>  Is it acceptable like something below
>>>>
>>>>  package Target;
>>>>  ...
>>>>  package Host;
>>>>  ...
>>>>  __PACKAGE__->belong_to('target' => 'Target', 'target_id');
>>>>  sub column_only_exists_in_target {
>>>>    my $self = shift;
>>>>    return $self->target->column_only_exists_in_target;
>>>>  }
>>>>
>>>>  well, it is not a good solution, but it could work, I think :)
>>>>
>>>>  On Fri, Jun 15, 2012 at 3:04 PM, Alex Erzin <eaa-home at yandex.ru> wrote:
>>>>>   Hello,
>>>>>
>>>>>   I need to implement table-per-class inheritance, as it simple made in Hibernate in Java (more details can be found here http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch10.html#inheritance-tablepersubclass),
>>>>>   but cannot find right way how to do it in DBIx::Class.
>>>>>
>>>>>   For example, I have two objects: Target (with properties ID, Description) and Host (ID, Hostname, IP), Host inherited from Target, and on table-level there are two tables Host and Target, joined by ID field.
>>>>>
>>>>>   CREATE  TABLE  `mydb`.`target` (
>>>>>    `target_id` INT NOT NULL ,
>>>>>    `description` VARCHAR(45) NULL ,
>>>>>    PRIMARY KEY (`target_id`) )
>>>>>
>>>>>   CREATE  TABLE `mydb`.`host` (
>>>>>    `target_id` INT NOT NULL ,
>>>>>    `hostname` VARCHAR(45) NULL ,
>>>>>    `ip` VARCHAR(45) NULL ,
>>>>>    PRIMARY KEY (`target_id`) ,
>>>>>    CONSTRAINT `fk_host_target`
>>>>>      FOREIGN KEY (`target_id` )
>>>>>      REFERENCES `mydb`.`target` (`target_id` )
>>>>>   )
>>>>>
>>>>>   How to implemeng there classes Target and Host, so it possible to write
>>>>>
>>>>>   print $target->id(), $targer->description()
>>>>>   print $host->id(), $host->description(), $host->hostname(), $host->ip()
>>>>>
>>>>>   ?
>>>>>
>>>>>   I have no ideas how to implement inheritance, and all my experiments are failed - from Host i cannot get access to parent properties like description.
>>>>>   Could you help me please (with examples)?
>>>>>
>>>>>   Thanks.
>>>>>
>>>>>   --
>>>>>   eaa@
>>>>>
>>>>>   _______________________________________________
>>>>>   List: http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbix-class
>>>>>   IRC: irc.perl.org#dbix-class
>>>>>   SVN: http://dev.catalyst.perl.org/repos/bast/DBIx-Class/
>>>>>   Searchable Archive: http://www.grokbase.com/group/dbix-class@lists.scsys.co.uk
>>>>  _______________________________________________
>>>>  List: http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbix-class
>>>>  IRC: irc.perl.org#dbix-class
>>>>  SVN: http://dev.catalyst.perl.org/repos/bast/DBIx-Class/
>>>>  Searchable Archive: http://www.grokbase.com/group/dbix-class@lists.scsys.co.uk
>>>  --
>>>  eaa@
>>>
>>>  _______________________________________________
>>>  List: http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbix-class
>>>  IRC: irc.perl.org#dbix-class
>>>  SVN: http://dev.catalyst.perl.org/repos/bast/DBIx-Class/
>>>  Searchable Archive: http://www.grokbase.com/group/dbix-class@lists.scsys.co.uk
>>
>> _______________________________________________
>> List: http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbix-class
>> IRC: irc.perl.org#dbix-class
>> SVN: http://dev.catalyst.perl.org/repos/bast/DBIx-Class/
>> Searchable Archive: http://www.grokbase.com/group/dbix-class@lists.scsys.co.uk
>
> --
> eaa@
>
> _______________________________________________
> List: http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbix-class
> IRC: irc.perl.org#dbix-class
> SVN: http://dev.catalyst.perl.org/repos/bast/DBIx-Class/
> Searchable Archive: http://www.grokbase.com/group/dbix-class@lists.scsys.co.uk