title: Getting following error on migration
body: <p>I am working on rails 2 project and am getting the following error while running rake tasks. Can someone help me out as what may be causing this.</p>
  
  <pre><code>[root@localhost webapp]# rake db:migrate
  (in /root/public/webapp)
  ==  CreateWhereKeywords: migrating ============================================
  -- create_table(:where_keywords)
  NOTICE:  CREATE TABLE will create implicit sequence "where_keywords_id_seq" for serial column "where_keywords.id"
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "where_keywords_pkey" for table "where_keywords"
     -&gt; 0.0838s
  -- execute("alter table where_keywords add constraint where_keyword foreign key (where_location_id) references \n        where_locations(id) on delete cascade")
  rake aborted!
  An error has occurred, this and all later migrations canceled:
  
  PGError: ERROR:  foreign key constraint "where_keyword" cannot be implemented
  DETAIL:  Key columns "where_location_id" and "id" are of incompatible types: character varying and integer.
  : alter table where_keywords add constraint where_keyword foreign key (where_location_id) references 
          where_locations(id) on delete cascade
  </code></pre>