Rails - Mar 2006 - Self-referential join model does not work

I have been trying to model a labeled graph using ActiveRecord (trunk
version). Basically, I have a ''Node'' model which represents a
node linking
to other nodes. Links (aka edges) are labeled (i.e., have a
''label''
attribute and other behavior). Thus I decided to model edges as an
''Edge''
model and use a ''has_many :trough'' association in the Node
model. However,
it just doesn''t work, regardless of how hard I''ve tried.

The database structure is as follows:

class InitialSchema < ActiveRecord::Migration
  def self.up
    create_table :nodes do |t|
      t.column :title, :string, :null => false
      t.column :body, :text, :null => false, :default =>
''''
    end
    create_table :edges do |t|
      t.column :node_id, :integer, :null => false
      t.column :related_node_id, :integer, :null => false
      t.column :label, :string, :null => false, :default =>
''''
    end
    add_index :edges, [:node_id, :related_node_id], :unique => true
  end
  def self.down
    drop_table :edges
    drop_table :nodes
  end
end

The two models are as follows:

class Node < ActiveRecord::Base
  validates_presence_of :title
  has_many :edges, :dependent => true
  has_many :related_nodes, :through => :edges, :class_name =>
''Node'', :foreign_key => ''node_id''
end

class Edge < ActiveRecord::Base
  belongs_to :node
  belongs_to :related_node, :class_name => ''Node'',
:foreign_key =>
''related_node_id''
  validates_uniqueness_of :related_node_id, :scope => :node_id
  validates_presence_of :node, :related_node  
end

In script/console I then create two nodes and link them with an edge as
follows:
>> from_node = Node.create :title => ''From''
>> to_node = Node.create :title => ''To''
>> e = Edge.create :node => from_node, :related_node => to_node
>> from_node.edges.find_first.related_node
=> #<Node:0xb7430ee4 @attributes={"body"=>"",
"title"=>"To", "id"=>"2"}>

SO FAR SO GOOD! but if I ask the ''from_node'' for
''related_nodes'' this is
what I get back!!!
>> from_node.edges.related_nodes.find_first
=> #<Node:0xb742e20c @attributes={"body"=>"",
"title"=>"From", "id"=>"1"}>

Same result even if I change :foreign_key in the Node model from
''node_id''
to ''related_node_id''. Furthermore, :association_foreign_key is
not accepted
as a parameter to has_many :through associations.

Does anybody have a clue of what I am doing wrong here? Or is it that Rails
1.1 does not support self-referential join models?

Thanx in advance for the help and consideration,

Edoardo "Dado" Marcora

See if the patch at http://dev.rubyonrails.org/ticket/4289 works for
you.  It adds the :association_foreign_key to has_many.

On 3/14/06, Edoardo Dado Marcora <marcora@caltech.edu>
wrote:
> I have been trying to model a labeled graph using ActiveRecord (trunk
> version). Basically, I have a ''Node'' model which
represents a node linking
> to other nodes. Links (aka edges) are labeled (i.e., have a
''label''
> attribute and other behavior). Thus I decided to model edges as an
''Edge''
> model and use a ''has_many :trough'' association in the
Node model. However,
> it just doesn''t work, regardless of how hard I''ve tried.
>
> The database structure is as follows:
>
> class InitialSchema < ActiveRecord::Migration
>   def self.up
>     create_table :nodes do |t|
>       t.column :title, :string, :null => false
>       t.column :body, :text, :null => false, :default =>
''''
>     end
>     create_table :edges do |t|
>       t.column :node_id, :integer, :null => false
>       t.column :related_node_id, :integer, :null => false
>       t.column :label, :string, :null => false, :default =>
''''
>     end
>     add_index :edges, [:node_id, :related_node_id], :unique => true
>   end
>   def self.down
>     drop_table :edges
>     drop_table :nodes
>   end
> end
>
> The two models are as follows:
>
> class Node < ActiveRecord::Base
>   validates_presence_of :title
>   has_many :edges, :dependent => true
>   has_many :related_nodes, :through => :edges, :class_name =>
> ''Node'', :foreign_key => ''node_id''
> end
>
> class Edge < ActiveRecord::Base
>   belongs_to :node
>   belongs_to :related_node, :class_name => ''Node'',
:foreign_key =>
> ''related_node_id''
>   validates_uniqueness_of :related_node_id, :scope => :node_id
>   validates_presence_of :node, :related_node
> end
>
> In script/console I then create two nodes and link them with an edge as
> follows:
>
> >> from_node = Node.create :title => ''From''
> >> to_node = Node.create :title => ''To''
> >> e = Edge.create :node => from_node, :related_node => to_node
> >> from_node.edges.find_first.related_node
> => #<Node:0xb7430ee4 @attributes={"body"=>"",
"title"=>"To", "id"=>"2"}>
>
> SO FAR SO GOOD! but if I ask the ''from_node'' for
''related_nodes'' this is
> what I get back!!!
>
> >> from_node.edges.related_nodes.find_first
> => #<Node:0xb742e20c @attributes={"body"=>"",
"title"=>"From", "id"=>"1"}>
>
> Same result even if I change :foreign_key in the Node model from
''node_id''
> to ''related_node_id''. Furthermore,
:association_foreign_key is not accepted
> as a parameter to has_many :through associations.
>
> Does anybody have a clue of what I am doing wrong here? Or is it that Rails
> 1.1 does not support self-referential join models?
>
> Thanx in advance for the help and consideration,
>
> Edoardo "Dado" Marcora
>
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

Thanx for adding the ticket and for coming up with the patch. I am sure 
things will be resolved quickly in rails/trunk.

Lee Marlow wrote:
> See if the patch at http://dev.rubyonrails.org/ticket/4289 works for
> you.  It adds the :association_foreign_key to has_many.

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

Did you get this sorted?

I got something that works for me using the lovely :through. I copied
it onto a blogger account since it would have been real messy here....

http://rubbishshoes.blogspot.com/2006/03/self-referential-many-many-using.html

beers
-h

On 3/15/06, Edoardo Dado Marcora <marcora@caltech.edu>
wrote:
> I have been trying to model a labeled graph using ActiveRecord (trunk
> version). Basically, I have a ''Node'' model which
represents a node linking
> to other nodes. Links (aka edges) are labeled (i.e., have a
''label''
> attribute and other behavior). Thus I decided to model edges as an
''Edge''
> model and use a ''has_many :trough'' association in the
Node model. However,
> it just doesn''t work, regardless of how hard I''ve tried.
>
> The database structure is as follows:
>
> class InitialSchema < ActiveRecord::Migration
>   def self.up
>     create_table :nodes do |t|
>       t.column :title, :string, :null => false
>       t.column :body, :text, :null => false, :default =>
''''
>     end
>     create_table :edges do |t|
>       t.column :node_id, :integer, :null => false
>       t.column :related_node_id, :integer, :null => false
>       t.column :label, :string, :null => false, :default =>
''''
>     end
>     add_index :edges, [:node_id, :related_node_id], :unique => true
>   end
>   def self.down
>     drop_table :edges
>     drop_table :nodes
>   end
> end
>
> The two models are as follows:
>
> class Node < ActiveRecord::Base
>   validates_presence_of :title
>   has_many :edges, :dependent => true
>   has_many :related_nodes, :through => :edges, :class_name =>
> ''Node'', :foreign_key => ''node_id''
> end
>
> class Edge < ActiveRecord::Base
>   belongs_to :node
>   belongs_to :related_node, :class_name => ''Node'',
:foreign_key =>
> ''related_node_id''
>   validates_uniqueness_of :related_node_id, :scope => :node_id
>   validates_presence_of :node, :related_node
> end
>
> In script/console I then create two nodes and link them with an edge as
> follows:
>
> >> from_node = Node.create :title => ''From''
> >> to_node = Node.create :title => ''To''
> >> e = Edge.create :node => from_node, :related_node => to_node
> >> from_node.edges.find_first.related_node
> => #<Node:0xb7430ee4 @attributes={"body"=>"",
"title"=>"To", "id"=>"2"}>
>
> SO FAR SO GOOD! but if I ask the ''from_node'' for
''related_nodes'' this is
> what I get back!!!
>
> >> from_node.edges.related_nodes.find_first
> => #<Node:0xb742e20c @attributes={"body"=>"",
"title"=>"From", "id"=>"1"}>
>
> Same result even if I change :foreign_key in the Node model from
''node_id''
> to ''related_node_id''. Furthermore,
:association_foreign_key is not accepted
> as a parameter to has_many :through associations.
>
> Does anybody have a clue of what I am doing wrong here? Or is it that Rails
> 1.1 does not support self-referential join models?
>
> Thanx in advance for the help and consideration,
>
> Edoardo "Dado" Marcora
>
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>