Rails - Jun 2006 - habtm has_many through and foreign keys

I have two models
Role and Task
..and a join table/model RoleTask

Now both roles and tasks have id as a primary key and name which is a 
unique identifier

I want the join table to hold role_id and task_name

I''ve tried using habtm with foreign key and association foreign keys
set
up and I''ve tried using has_many :through
..but they all seem to someone want to work with the primary keys of 
both roles and tasks.

Do I need to set the primary key of tasks to be the name field?

thanks in advance
levent

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