Robby on Rails

$sql = $db->prepare("SELECT seq.relname::text
                        FROM pg_class src, pg_class seq, pg_namespace, pg_attribute,
                        pg_depend
                        WHERE
                            pg_depend.refobjsubid = pg_attribute.attnum AND
                            pg_depend.refobjid = src.oid AND
                            seq.oid = pg_depend.objid AND
                            src.relnamespace = pg_namespace.oid AND
                            pg_attribute.attrelid = src.oid AND
                            pg_namespace.nspname = ? AND
                            src.relname = ? AND
                            pg_attribute.attname = ?");

testingdb=# \d legacy.foobar
                                     Table "legacy.foobar" 
  Column   |         Type          |                         Modifiers                          
-----------+-----------------------+------------------------------------------------------------
 foobar_id | integer               | not null default nextval('legacy.old_sequence_name'::text)
 name      | character varying(40) | 
Indexes:
    "foobar_pkey" PRIMARY KEY, btree (foobar_id)

testingdb=# INSERT INTO legacy.foobar (name) VALUES ('abc')
testingdb-# ;
INSERT 17514 1
testingdb=# SELECT * FROM legacy.foobar ;
 foobar_id | name 
-----------+------
       106 | abc
(1 row)

=# \d legacy.people
                                       Table "legacy.people" 
  Column   |         Type          |                           Modifiers                           
-----------+-----------------------+---------------------------------------------------------------
 people_id | integer               | not null default nextval('legacy.people_people_id_seq'::text)
 name      | character varying(50) | 
Indexes:
    "people_pkey" PRIMARY KEY, btree (people_id)

=# \d foo.people
                                       Table "foo.people" 
  Column   |         Type          |                         Modifiers                          
-----------+-----------------------+------------------------------------------------------------
 people_id | integer               | not null default nextval('foo.people_people_id_seq'::text)
 name      | character varying(50) | 
Indexes:
    "people_pkey" PRIMARY KEY, btree (people_id)      

# SELECT adsrc FROM pg_attrdef WHERE adrelid = (SELECT oid FROM pg_class WHERE relname = 'people');
ERROR:  more than one row returned by a subquery used as an expression  

class LegacyTable < ActiveRecord::Base
  def self.table_name() "legacy.foobar" end

  # new option for this
  set_primary_key "foobar_id", :sequence => "legacy.old_sequence_name" 
end