Through associations on tables with non-standard primary keys

I cannot seem to get through associations working properly on tables
that have non standard primary keys.

class Address < ActiveRecord::Base
  set_primary_key "address_id"
  has_many :investor_addresses
  has_many :investors, :through => :investor_addresses, :source =>
:investor
end

class Investor < ActiveRecord::Base
  set_primary_key "pid"
  has_many :investor_addresses
  has_many :addresses, :through => :investor_addresses, :source =>
:address
end

class InvestorAddress < ActiveRecord::Base
  set_primary_key "investor_address_id"
  belongs_to :investor, :foreign_key => "pid"
  belongs_to :address, :foreign_key => "address_id"
end

The Investors table has primary key pid.
The Addresses table has primary key address_id.
The investor_addresses table has a primary key investor_address and
also columns pid and address_id.

To me this should work but when I do:
i = Investor.find(6493)
i.addresses

Active record seems to think the investor_addresses table has a column
called investor_id. Why wont it use pid?

ActiveRecord::StatementInvalid: PGError: ERROR: column
investor_addresses.investor_id does not exist
: SELECT addresses.* FROM addresses INNER JOIN investor_addresses ON
addresses.address_id = investor_addresses.address_id WHERE
(investor_addresses.investor_id = 6493)
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/connection_adapters/abstract_adapter.rb:120:in
`log'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/connection_adapters/postgresql_adapter.rb:148:in
`execute'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/connection_adapters/postgresql_adapter.rb:361:in
`select'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/connection_adapters/postgresql_adapter.rb:129:in
`select_all'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:390:in
`find_by_sql'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:924:in
`find_every'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:381:in
`find'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations/has_many_through_association.rb:54:in
`find_target'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations/association_proxy.rb:116:in
`load_target'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations/association_proxy.rb:109:in
`method_missing'
        from
/sw/var/lib/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations/has_many_through_association.rb:47:in
`method_missing'
        from /sw/lib/ruby/1.8/irb.rb:298:in `output_value'
        from /sw/lib/ruby/1.8/irb.rb:151:in `eval_input'
        from /sw/lib/ruby/1.8/irb.rb:259:in `signal_status'
        from /sw/lib/ruby/1.8/irb.rb:147:in `eval_input'
        from /sw/lib/ruby/1.8/irb.rb:146:in `eval_input'
        from /sw/lib/ruby/1.8/irb.rb:70:in `start'
        from /sw/lib/ruby/1.8/irb.rb:69:in `start'

Gonna answer my own question here. It should be as follows:

class Address < ActiveRecord::Base
  set_primary_key "address_id"
  has_many :investor_addresses, :foreign_key => "address_id"
  has_many :investors, :through => :investor_addresses
end

class Investor < ActiveRecord::Base
  set_primary_key "pid"
  has_many :investor_addresses, :foreign_key => "pid"
  has_many :addresses, :through => :investor_addresses
end

class InvestorAddress < ActiveRecord::Base
  set_primary_key "investor_address_id"
  belongs_to :investor, :foreign_key => "pid"
  belongs_to :address, :foreign_key => "address_id"
end