I'm confused with "package Host; extends 'Base';"
I expect "extends 'Target'", not 'Base'. Is it correct?

15.06.2012, 12:06, "Hailin Hu" <i...@h2l.name>:
> 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-h...@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" <bti...@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-h...@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...@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-h...@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@
>>>>>>
>>>>>>    _______________________________________________
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>>>>>   _______________________________________________
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>>>>   --
>>>>   eaa@
>>>>
>>>>   _______________________________________________
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>>>  _______________________________________________
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>>  --
>>  eaa@
>>
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>
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-- 
eaa@

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