Rails - Dec 2008 - one association from two

I''m working on a two-to-many relationship that works fine from the
child object''s perspective but not from the parent''s.    The
imperfect, yet functional code looks like this:
-------------------------------------------------------------------
class PrimaryTable < ActiveRecord::Base
  has_many :secondary_tables_1 ,
            :foreign_key => :A_primary_table_id,
           :class_name => "SecondaryTable"
 has_many :secondary_tables_2 ,
           :foreign_key => :B_primary_table_id,
           :class_name => "SecondaryTable"
end

class SecondaryTable < ActiveRecord::Base
  belongs_to :A_primary_table,
           :foreign_key => :A_primary_table_id,
           :class_name => "PrimaryTable"
  belongs_to :B_primary_table,
           :foreign_key=> :B_primary_table_id,
            :class_name => "PrimaryTable"
end
------------------------------------------------------------------------------------------

But, I don''t want to have two linking fields up *and* two linking
fields down.  I only want one linking field down.  I would like to
lump these parent to child relationships into one associated link...
doing something like this:

------------------------------------------------------------------------------------------

class PrimaryTable < ActiveRecord::Base
  has_many :secondary_tables ,
           :foreign_key => :A_primary_table_id,
           :foreign_key => :B_primary_table_id,
           :class_name => "SecondaryTable"
end

-------------------------------------------------

...but only one of the two links (the ones to "B_primary_table") shows
up this way.


Does any body have any idea how to do this?  I would think this would
be an easy thing to do.

Dave


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dschruth wrote:
> I''m working on a two-to-many relationship that works fine from the
> child object''s perspective but not from the parent''s.   
The
> imperfect, yet functional code looks like this:
> -------------------------------------------------------------------
> class PrimaryTable < ActiveRecord::Base
>   has_many :secondary_tables_1 ,
>             :foreign_key => :A_primary_table_id,
>            :class_name => "SecondaryTable"
>  has_many :secondary_tables_2 ,
>            :foreign_key => :B_primary_table_id,
>            :class_name => "SecondaryTable"
> end
> 
> class SecondaryTable < ActiveRecord::Base
>   belongs_to :A_primary_table,
>            :foreign_key => :A_primary_table_id,
>            :class_name => "PrimaryTable"
>   belongs_to :B_primary_table,
>            :foreign_key=> :B_primary_table_id,
>             :class_name => "PrimaryTable"
> end
>
------------------------------------------------------------------------------------------
> 
> But, I don''t want to have two linking fields up *and* two linking
> fields down.  I only want one linking field down.  I would like to
> lump these parent to child relationships into one associated link...
> doing something like this:
> 
>
------------------------------------------------------------------------------------------
> 
> class PrimaryTable < ActiveRecord::Base
>   has_many :secondary_tables ,
>            :foreign_key => :A_primary_table_id,
>            :foreign_key => :B_primary_table_id,
>            :class_name => "SecondaryTable"
> end
> 
> -------------------------------------------------
> 
> ...but only one of the two links (the ones to "B_primary_table")
shows
> up this way.
Using the :finder_sql option to has_many, you''ll have to write
custom SQL that does an "or" on the two foreign keys.

-- 
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