Rails - Oct 2007 - Two foreign keys in model pointing at same table issue

Hello all.  :)

I have a student model with two foreign keys (FK).  Both of these keys
point at a county table.

These are the column statements for the two FK:
  t.column :nationality_id, :integer, :null => FALSE
  t.column :current_location_id, :integer, :null => FALSE

I then linked these to FK into my Student and Countries models:

class StStudent < ActiveRecord::Base
  belongs_to :nationality_id, :class_name => "GlCountry",
:foreign_key
=> "nationality_id"
  belongs_to :current_location_id, :class_name => "GlCountry",
:foreign_key => "current_location_id"

class GlCountry < ActiveRecord::Base
  has_many :st_students, :class_name => "StStudent", :foreign_key
=>
"nationality_id"
  has_many :st_students, :class_name => "StStudent", :foreign_key
=>
"current_location_id"

OK, so now things look peachy.  I can do a
StStudent.nationality_id.printable_name and see happy things.

However, when I attempt to use this setup in the ''New Student''
and ''Edit
Student'' actions the troubles start!

My controller defines the countries like this:
  @countries = GlCountry.find(:all, :select => "id,
printable_name",
:order => ''printable_name'').map {|u|
[u.printable_name,u.id]}

I then make dropdowns like this in the ''_forms'' partial:
  <p><label for="st_student_nationality_id">Nationality
(*)</label><br/>
  <%= select(''st_student'',
''nationality_id'', @countries)%></p>

And now everything breaks.  In the ''New'' view I see the object
ID for a
GlCountry object in the dropdown.  If I try to save a new student or
edit an existing one I see a ''GlCountry expected, got String''
error.

The dropdowns won''t select existing values when editing a student.  I
can do it manually, but I have to type this:  :selected =>
st_student.nationality_id.id.

I believe that the linking of the two models via the '':class_name
=>''
statements in the models has created GlCountry objects that are
assciated w/ my StStudent object. It doesn''t seem to just return the
values as I would have wished.

Does anyone have any advice or solutions on this?  Has anyone else
linked FK using the '':class_name =>'' method, and if so, how
did you do
it?

Many thanks!
Nathan
-- 
Posted via http://www.ruby-forum.com/.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

On 23 Oct 2007, at 17:44, Nathan Rasch wrote:
> And now everything breaks.  In the ''New'' view I see the
object ID
> for a
> GlCountry object in the dropdown.  If I try to save a new student or
> edit an existing one I see a ''GlCountry expected, got
String'' error.
>
> The dropdowns won''t select existing values when editing a student.
I
> can do it manually, but I have to type this:  :selected =>
> st_student.nationality_id.id.
>
> I believe that the linking of the two models via the '':class_name
=>''
> statements in the models has created GlCountry objects that are
> assciated w/ my StStudent object. It doesn''t seem to just return
the
> values as I would have wished.
>
I think the problem is that the association name is the same as the  
foreign key name. When populating the select, normally you would look  
at foo_id to see which Foo should be the selected one. However in  
your case sending nationality_id to an instance of Student returns a  
GlCountry object, not an id. Similarly the form stuff will be trying  
to set nationality_id to be the id of the chosen object, but since  
nationality_id is actually the association that will break too.

You should probably change it to this:

class StStudent < ActiveRecord::Base
   belongs_to :nationality, :class_name => "GlCountry",
:foreign_key
=> "nationality_id"
   belongs_to :current_location, :class_name => "GlCountry",
:foreign_key => "current_location_id"
end

Fred