Rails - Jan 2006 - nuby: do models have to inherit directly from ActiveRecord?

Hello,
 
I have a few models -- book, cd, dvd -- for which I''d like to have an
abstract base superclass to hold some common stuff. That abstract class, I
was thinking, would inherit from ActiveRecord.
 
Didn''t work, though, and looking around, I found this:
<http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel>
http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel. Which looks
pretty hackish to me. Is there any best way or recommendations on how to
achieve this kind of behavior? I know I could modify ActiveRecord directly,
but that seems brittle -- to run my app on later versions of rails, I''d
have
to remember to re-modify ActiveRecord.
 
What''s really brittle, though, is my brain. This is my first RoR app,
and
parts of rails (convention over config, built-in ORM and testing) I
immediately loved. But some stuff seems like it would be, well, [puts on
fireproof suit] easier in Java. I''m still sort of waiting for it all to
come
together in my mind.
 
Anyways, apologies for being a dunce. Any guidance on how to best handle the
abstract base class question would be much appreciated.
 
John
http://fryolator.com
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You should take a look at Single Table Inheritance (STI):
http://wiki.rubyonrails.com/rails/pages/SingleTableInheritance

/ CJ

On 1/14/06, John McGrath <jmcgrath@whoi.edu>
wrote:
>
>
> Hello,
>
> I have a few models -- book, cd, dvd -- for which I''d like to have
an
> abstract base superclass to hold some common stuff. That abstract class, I
> was thinking, would inherit from ActiveRecord.
>
> Didn''t work, though, and looking around, I found this:
> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel.
> Which looks pretty hackish to me. Is there any best way or recommendations
> on how to achieve this kind of behavior? I know I could modify ActiveRecord
> directly, but that seems brittle -- to run my app on later versions of
> rails, I''d have to remember to re-modify ActiveRecord.
>
> What''s really brittle, though, is my brain. This is my first RoR
app, and
> parts of rails (convention over config, built-in ORM and testing) I
> immediately loved. But some stuff seems like it would be, well, [puts on
> fireproof suit] easier in Java. I''m still sort of waiting for it
all to come
> together in my mind.
>
> Anyways, apologies for being a dunce. Any guidance on how to best handle
the
> abstract base class question would be much appreciated.
>
> John
> http://fryolator.com
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
>
>

Have you tried using Ruby module as mixin?

Chris

On 1/13/06, John McGrath <jmcgrath@whoi.edu>
wrote:
>
> Hello,
>
> I have a few models -- book, cd, dvd -- for which I''d like to have
an
> abstract base superclass to hold some common stuff. That abstract class, I
> was thinking, would inherit from ActiveRecord.
>
> Didn''t work, though, and looking around, I found this:
> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel.
> Which looks pretty hackish to me. Is there any best way or recommendations
> on how to achieve this kind of behavior? I know I could modify ActiveRecord
> directly, but that seems brittle -- to run my app on later versions of
> rails, I''d have to remember to re-modify ActiveRecord.
>
> What''s really brittle, though, is my brain. This is my first RoR
app, and
> parts of rails (convention over config, built-in ORM and testing) I
> immediately loved. But some stuff seems like it would be, well, [puts on
> fireproof suit] easier in Java. I''m still sort of waiting for it
all to come
> together in my mind.
>
> Anyways, apologies for being a dunce. Any guidance on how to best handle
the
> abstract base class question would be much appreciated.
>
> John
> http://fryolator.com
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
>
>

On Jan 14, 2006, at 12:11 AM, rails-request@lists.rubyonrails.org wrote:
> I have a few models -- book, cd, dvd -- for which I''d like to have
an
> abstract base superclass to hold some common stuff. That abstract  
> class, I
> was thinking, would inherit from ActiveRecord.
>
> Didn''t work, though, and looking around, I found this:
> <http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel>
> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel.  
> Which looks
> pretty hackish to me. Is there any best way or recommendations on  
> how to
> achieve this kind of behavior? I know I could modify ActiveRecord  
> directly,
> but that seems brittle -- to run my app on later versions of rails,  
> I''d have
> to remember to re-modify ActiveRecord.
That''s how you do it.
> What''s really brittle, though, is my brain. This is my first RoR  
> app, and
> parts of rails (convention over config, built-in ORM and testing) I
> immediately loved. But some stuff seems like it would be, well,  
> [puts on
> fireproof suit] easier in Java. I''m still sort of waiting for it  
> all to come
> together in my mind.
A few things are harder than they should be, like subclassing  
ActiveRecord::Base.  Rather than make the common thing easy,  
ActiveRecord reserves subclassing for a seldom-used feature.
> Anyways, apologies for being a dunce. Any guidance on how to best  
> handle the
> abstract base class question would be much appreciated.
Bite the bullet and add those methods.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com

On Jan 14, 2006, at 12:11 AM, rails-request@lists.rubyonrails.org wrote:
> On 1/13/06, John McGrath <jmcgrath@whoi.edu> wrote:
>
>> I have a few models -- book, cd, dvd -- for which I''d like to
have an
>> abstract base superclass to hold some common stuff. That abstract  
>> class, I
>> was thinking, would inherit from ActiveRecord.
>>
>> Didn''t work, though, and looking around, I found this:
>> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel.
>> Which looks pretty hackish to me.
>
> Have you tried using Ruby module as mixin?
Ruby is an OO language so subclassing should Just Work.  The single  
table inheritance hack prevents developers from performing code reuse  
the natural OO way.  There''s more use cases for code reuse via  
inheritance than for single table inheritance.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com

John McGrath wrote:
> I have a few models -- book, cd, dvd -- for which I''d like to have
an
> abstract base superclass to hold some common stuff. That abstract 
> class, I was thinking, would inherit from ActiveRecord.
>  
> Didn''t work, though, and looking around, I found this: 
> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel. Which 
> looks pretty hackish to me. Is there any best way or recommendations on 
> how to achieve this kind of behavior? I know I could modify ActiveRecord 
> directly, but that seems brittle -- to run my app on later versions of 
> rails, I''d have to remember to re-modify ActiveRecord.
What I did once was to put the common stuff in a module, called say Media
in your case, and put ''include Media'' at the top of each model
class.

Instance methods will include directly, but for class methods that you
want to call without using the "Media." prefix you have to define a
self.included(model) method in the module that defines the class methods
in a model.class_eval block.

-- 
We develop, watch us RoR, in numbers too big to ignore.

Since ActiveRecord creates a direct mapping to database tables, there would
be a case here for mixins. STI is not a seldom used feature, and Ruby
provides the mixin facility just for these types of situations where you
need to inherit functionality from two places.

Joshua Sierles

On 1/14/06, Eric Hodel <drbrain@segment7.net>
wrote:
>
> On Jan 14, 2006, at 12:11 AM, rails-request@lists.rubyonrails.org wrote:
>
> > On 1/13/06, John McGrath <jmcgrath@whoi.edu> wrote:
> >
> >> I have a few models -- book, cd, dvd -- for which I''d
like to have an
> >> abstract base superclass to hold some common stuff. That abstract
> >> class, I
> >> was thinking, would inherit from ActiveRecord.
> >>
> >> Didn''t work, though, and looking around, I found this:
> >> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel.
> >> Which looks pretty hackish to me.
> >
> > Have you tried using Ruby module as mixin?
>
> Ruby is an OO language so subclassing should Just Work.  The single
> table inheritance hack prevents developers from performing code reuse
> the natural OO way.  There''s more use cases for code reuse via
> inheritance than for single table inheritance.
>
> --
> Eric Hodel - drbrain@segment7.net - http://segment7.net
> This implementation is HODEL-HASH-9600 compliant
>
> http://trackmap.robotcoop.com
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
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On 1/13/06, John McGrath <jmcgrath@whoi.edu>
wrote:
>
>
> Hello,
>
> I have a few models -- book, cd, dvd -- for which I''d like to have
an
> abstract base superclass to hold some common stuff. That abstract class, I
> was thinking, would inherit from ActiveRecord.
I think this applies:
http://blogs.pragprog.com/cgi-bin/pragdave.cgi/Tech/Ruby/Connections.rdoc

You can''t do:
class Media < AR; end
class Book < Media; end
class CD < Media; end;

?

Joe Van Dyk wrote:
> On 1/13/06, John McGrath <jmcgrath@whoi.edu> wrote:
>>
>>
>> Hello,
>>
>> I have a few models -- book, cd, dvd -- for which I''d like to
have an
>> abstract base superclass to hold some common stuff. That abstract
class, I
>> was thinking, would inherit from ActiveRecord.
> 
> I think this applies:
> http://blogs.pragprog.com/cgi-bin/pragdave.cgi/Tech/Ruby/Connections.rdoc
> 
> You can''t do:
> class Media < AR; end
> class Book < Media; end
> class CD < Media; end;
> 
> ?
But you CAN do:

module Media
 #...
end

class Book < AR
 include Media
end

class CD < AR
 include Media
end


-- 
Posted via http://www.ruby-forum.com/.

Jules Jacobs wrote:
> Joe Van Dyk wrote:
>>
>>You can''t do:
>>class Media < AR; end
>>class Book < Media; end
>>class CD < Media; end;
>>
>>?
> 
> 
> But you CAN do:
> 
> module Media
>  #...
> end
> 
> class Book < AR
>  include Media
> end
> 
> class CD < AR
>  include Media
> end
> 
Just to clarify here: Joe was NOT saying that you CAN''T have a base
class... note the "?"
after the "You can''t do:" bit. He was saying "why
can''t you just do...?", right Joe?

It seems that either approach will work, though now I''m even more
confused. I thought the
STI requirement in rails precluded base model classes (that don''t map
to tables). From the
Dave Thomas blog entry it looks like it''s okay as long as you
don''t try to call db methods
on the base class.

right?

b

On 1/14/06, Ben Munat <bent@munat.com> wrote:
> Jules Jacobs wrote:
> > Joe Van Dyk wrote:
> >>
> >>You can''t do:
> >>class Media < AR; end
> >>class Book < Media; end
> >>class CD < Media; end;
> >>
> >>?
> >
> >
> > But you CAN do:
> >
> > module Media
> >  #...
> > end
> >
> > class Book < AR
> >  include Media
> > end
> >
> > class CD < AR
> >  include Media
> > end
> >
>
> Just to clarify here: Joe was NOT saying that you CAN''T have a
base class... note the "?"
> after the "You can''t do:" bit. He was saying "why
can''t you just do...?", right Joe?
Yes, that''s right.
> It seems that either approach will work, though now I''m even more
confused. I thought the
> STI requirement in rails precluded base model classes (that don''t
map to tables). From the
> Dave Thomas blog entry it looks like it''s okay as long as you
don''t try to call db methods
> on the base class.
>
> right?
Yeah, I think it''s fine as long as the base class is abstract (i.e.
you don''t try to instantiate it or try to call any db methods with
it).

On Jan 14, 2006, at 7:17 AM, rails-request@lists.rubyonrails.org wrote:
> On 1/14/06, Eric Hodel <drbrain@segment7.net> wrote:
>>
>> On Jan 14, 2006, at 12:11 AM, rails-request@lists.rubyonrails.org  
>> wrote:
>>
>>> On 1/13/06, John McGrath <jmcgrath@whoi.edu> wrote:
>>>
>>>> I have a few models -- book, cd, dvd -- for which I''d
like to
>>>> have an
>>>> abstract base superclass to hold some common stuff. That
abstract
>>>> class, I
>>>> was thinking, would inherit from ActiveRecord.
>>>>
>>>> Didn''t work, though, and looking around, I found this:
>>>> http://wiki.rubyonrails.com/rails/pages/HowtoMakeAbstractModel.
>>>> Which looks pretty hackish to me.
>>>
>>> Have you tried using Ruby module as mixin?
>>
>> Ruby is an OO language so subclassing should Just Work.  The single
>> table inheritance hack prevents developers from performing code reuse
>> the natural OO way.  There''s more use cases for code reuse via
>> inheritance than for single table inheritance.
>
> Since ActiveRecord creates a direct mapping to database tables,  
> there would
> be a case here for mixins. STI is not a seldom used feature, and Ruby
> provides the mixin facility just for these types of situations  
> where you
> need to inherit functionality from two places.
Proper factoring of code should not be made difficult in the  
interests of a feature than not everybody uses.  It would make more  
sense to tell people "call this method to set this class up for STI"  
then to tell people "sorry, you can''t use inheritance with  
ActiveRecord::Base the way you do everywhere else in Ruby and in  
every other OO language unless you add this hack".

You should certainly not need to use Module#include to hack around  
broken inheritance.  Mixins are for functionality that does not fit  
in the class hierarchy.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com