Rails - Dec 2006 - representing a graph

I am representing a graph structrure in my DB. I have a table for nodes
(which holds node names for now) and a table for segments/links. Each
segment has the id-s of its 2 end-nodes.
How do i specify this in the Rails model for a Segment ? I can''t say
belongs_to twice ...
Is there a better way to do this ?

Thanks

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

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Self referential has_many :through, with the segment as the join model?

-faisal

On Dec 17, 2006, at 8:16 PM, hapciu wrote:
> I am representing a graph structrure in my DB. I have a table for  
> nodes
> (which holds node names for now) and a table for segments/links. Each
> segment has the id-s of its 2 end-nodes.
> How do i specify this in the Rails model for a Segment ? I can''t
say
> belongs_to twice ...
> Is there a better way to do this ?
>
> Thanks
>
> -- 
> Posted via http://www.ruby-forum.com/.
>
> >

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On Dec 17, 8:16 pm, hapciu
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> I am representing a graph structrure in my DB. I have a table for nodes
> (which holds node names for now) and a table for segments/links. Each
> segment has the id-s of its 2 end-nodes.
> How do i specify this in the Rails model for a Segment ? I can''t
say
> belongs_to twice ...
> Is there a better way to do this ?
Something along these lines?  This creates a directed graph, you would
just add two segments for each node pair with the source/target
reversed if you want an undirected graph.

## Models:

class Node < ActiveRecord::Base
  has_many :segments
  has_many :nodes, :through => :segments, :source => :target
end

class Segment < ActiveRecord::Base
  belongs_to :source, :class_name => "Node"
  belongs_to :target, :class_name => "Node"
end

## Migrations

create_table "nodes" do |t|
  t.column "name", :string
end
create_table "segments" do |t|
  t.column "source_id", :integer
  t.column "target_id", :integer
end

Best,

-r
> 
> Thanks
> 
> --
> Posted viahttp://www.ruby-forum.com/.

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Hi,


On Dec 17, 8:16 pm, hapciu
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>> I am representing a graph structrure in my DB. I have a table for 
>> nodes
>> (which holds node names for now) and a table for segments/links. Each
>> segment has the id-s of its 2 end-nodes.
>> How do i specify this in the Rails model for a Segment ? I
can''t say
>> belongs_to twice ...
>> Is there a better way to do this ?
Mybe you ''d like to have a look on nestedset theory and our 
implementation as plugin.
Thanks to some devs that helped a lot, our plugin has many tests and 
begins to work well.


Jean-Christophe Michel
--
symetrie.com

Better Nested Set for rails:
http://opensource.symetrie.com/trac/better_nested_set


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