Ruby Forum Ruby on Rails > I need untyped associations

I am in the process of trying to migrate to ROR from a home grown ORM,
but one stumbling block is ActiveRecord's typed associations and object
ID assignment scheme.   In the home grown system, I have a master table
which *all* objects are packed into and a master associative table which
holds *all* associations.  This allows each object, regardless of type,
to have a unique ID and thus it is easy to allow any object to associate
with any other object regardless of type.  This is handy for things such
as Folder objects which should be able to contain objects of arbitrary
type.  In ActiveState, it appears that ID's are only unique within a
particular table and associations require explicit type information (to
refer to a particular table).  So folder.contents can't really refer to
an arbitrary collection of objects.  I'm sure this has come up within
the ROR community before and there is probably an easy solution I'm
overlooking.

On Sun, Jan 08, 2006 at 04:54:10PM +0100, Sorenson wrote:
} I am in the process of trying to migrate to ROR from a home grown ORM,
} but one stumbling block is ActiveRecord's typed associations and 
object
} ID assignment scheme.   In the home grown system, I have a master 
table
} which *all* objects are packed into and a master associative table 
which
} holds *all* associations.  This allows each object, regardless of 
type,
} to have a unique ID and thus it is easy to allow any object to 
associate
} with any other object regardless of type.  This is handy for things 
such
} as Folder objects which should be able to contain objects of arbitrary
} type.  In ActiveState, it appears that ID's are only unique within a
} particular table and associations require explicit type information 
(to
} refer to a particular table).  So folder.contents can't really refer 
to
} an arbitrary collection of objects.  I'm sure this has come up within
} the ROR community before and there is probably an easy solution I'm
} overlooking.

The simplest thing is to create views in the DB, and triggers on the 
views
for inserting/updating, I expect.

--Greg

Polymorphic associations are on their way. DHH has added "preliminary 
support" in edgerails (from the changelog). I don't know what the 
performance impact would be for doing the whole db that way, but at 
least it will be along soon as an option. You can see a mention of this 
in here (the presentation is worth checking out):
http://weblog.rubyonrails.org/articles/2005/12/22/new-37signals-targets-for-rails-extraction

Sorenson wrote:
> I am in the process of trying to migrate to ROR from a home grown ORM,
> but one stumbling block is ActiveRecord's typed associations and object
> ID assignment scheme.   In the home grown system, I have a master table
> which *all* objects are packed into and a master associative table which
> holds *all* associations.  This allows each object, regardless of type,
> to have a unique ID and thus it is easy to allow any object to associate
> with any other object regardless of type.  This is handy for things such
> as Folder objects which should be able to contain objects of arbitrary
> type.  In ActiveState, it appears that ID's are only unique within a
> particular table and associations require explicit type information (to
> refer to a particular table).  So folder.contents can't really refer to
> an arbitrary collection of objects.  I'm sure this has come up within
> the ROR community before and there is probably an easy solution I'm
> overlooking.

Surely STI is all you need for this?

--
Alex

Alex Young wrote:
> Surely STI is all you need for this?
> 
> --
> Alex

I can see how STI would work if there is only one object table.  But 
this could get messy after there are more than a few branches on the 
inheritance tree.  I may still try it nonetheless.

This feature is provided using

belongs_to :files, :polymorphical => true

This requires you to have an additional _type column. in this case
file_type and file_id.

This belongs_to link would allow you to point to any other object in
the system without the need for a separate key registry.

In combination with the new :through associations you can then make a
link table.

class Folder < AR:B
  has_many :links
  has_many :content, :through => :links, :as => :object
end

def Link < AR:B
  belogns_to :folder
  belogns_to :object, :polymorphic => true
end

def RandomObject < AR:B
end


f = Folder.create
ro = RandomObject.create

f.links.create( :object => ro )

f.content #=> [ ro ]


All those features are only available in trunk and edge rails.





On 1/8/06, Sorenson <jsorenson@bellsouth.net> wrote:
> refer to a particular table).  So folder.contents can't really refer to
>
--
Tobi
http://jadedpixel.com    - modern e-commerce software
http://typo.leetsoft.com - Open source weblog engine
http://blog.leetsoft.com - Technical weblog

Hi Tobias,

This feature looks great...  Is there any documentation/tutorials 
written
for this yet?

I have rails 1.0.0 installed.  When are these features likely to be 
included
into the main gem?

Thanx in advance

Dan

This looks promising...

Tobias Luetke wrote:
> This feature is provided using
> 
> belongs_to :files, :polymorphical => true
> 
> This requires you to have an additional _type column. in this case
> file_type and file_id.
......

Hey I never got an email back from a library I released!
> On 1/12/06, Liquid <has.sox@gmail.com> wrote:

> This feature looks great...  Is there any documentation/tutorials written
> for this yet?

I use it heavily in Shopify and David uses it in his current project
as well so these features are certainly stableish. I don't think there
is any documentation at this point but if you download and watch
David's great talk at the Ruby and Snakes event he shows several
slides on the topic


--
Tobi
http://jadedpixel.com    - modern e-commerce software
http://typo.leetsoft.com - Open source weblog engine
http://blog.leetsoft.com - Technical weblog