Rails - May 2006 - belongs_to without referencing an id as a foreign key?

Hello everyone,

Here''s my problem for the day:  I have three tables that look a little
like
the following

table_a
 id

table_b
 id
 position
 table_a_id
 name

table_c
 id
 table_a_id
 table_b_position


There will be many rows in table_c that have the same table_a_id, and the
same table_b_position.  These will all be referencing the same name value in
table_b.  The row in table_b may or may not exist, and table_b_position is a
meaningful field with or without a corresponding row in table_b, so these
two reasons keep me from using table_b_id within table_c.  The natural
relationship here is for table_c to belong_to table_b, but I do not know how
to do this.  Any ideas?

Thanks!
Zack
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