HABTM question

is it possible you are describing a has-many relationship and not a
has-and-belongs-to-many relationship?

anyway, for a habtm relationship, i think the convention would be to
not hold any of the data about states in the address table. instead the
join table contains info about the addresses table and states table.
then rails knows what you want to do when you tell it to use an habtm

if you're dealing with a legacy system:

class State < ActiveRecord::Base
  set_primary_key "statecode"
  has and belongs_to_many :addresses, :foreign_key => "statecode"

class Address < ActiveRecord::Base
  has_and_belongs_to_many :states, :association_foreign_key => "statecode"

where your states table is:

statecode (PK)

and your join table, addresses_states, is


if you are designing from scratch, just use an id column in the states
table and do away with all the extra work above.

the argument is that any column that carries a meaning, no matter if
it's unique or not, should not be used as a primary key field. the id
column's only purpose is to uniquely identify that row and should
carry no meaning/purpose beyond that.