Postgres error on insert

[Mike Summers]

Trying to insert a row into a model that has a composite key the generated sql is asking for an array return value from Postgres:

{"city_id"=>"14000", "state_id"=>"17", "name"=>"City of Chicago", "feature_class"=>"Civil", "county_id"=>"031", "census_class_code"=>"C5"}

rake aborted!

PG::Error: ERROR:  column "[:state_id, :city_id]" does not exist

LINE 1: ...ES ($1, $2, $3, $4, $5, $6, $7, $8, $9) RETURNING "[:state_i...

                                                             ^

: INSERT INTO "cities" ("census_class_code", "city_id", "created_at", "geog", "geom", "name", "state_id", "subdivision_code", "updated_at") VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9) RETURNING "[:state_id, :city_id]"

Is the returning [:state_id, :city_id] correct?

Postgres table:

      Column       |            Type             | Modifiers | Storage  | Stats target | Description 

-------------------+-----------------------------+-----------+----------+--------------+-------------

 city_id           | integer                     | not null  | plain    |              | 

 state_id          | integer                     | not null  | plain    |              | 

 name              | character varying(255)      |           | extended |              | 

 subdivision_code  | integer                     |           | plain    |              | 

 census_class_code | character varying(255)      |           | extended |              | 

 created_at        | timestamp without time zone | not null  | plain    |              | 

 updated_at        | timestamp without time zone | not null  | plain    |              | 

 geom              | postgis.geometry            |           | main     |              | 

 geog              | postgis.geometry(Point)     |           | main     |              | 

Indexes:

    "cities_pkey" PRIMARY KEY, btree (city_id, state_id)

City model:

class City < ActiveRecord::Base

  self.primary_key = :state_id, :city_id

  has_many :addresses

  belongs_to :state

  has_and_belongs_to_many :zip_codes, foreign_key: [:state_id, :city_id]

  has_and_belongs_to_many :counties, foreign_key: [:state_id, :city_id]

  attr_accessible :city_id, :name, :state_id, :census_class_code

end

TIA.

[Mike Summers]

Pilot error, 

self.primary_key = :state_id, :city_id 

should of course be 

self.primary_keys = :state_id, :city_id