add support use string FK with integer PK

db/migrate/20121009205010_postgres_create_integer_cast.rb

@@ -0,0 +1,15 @@
+class PostgresCreateIntegerCast < ActiveRecord::Migration
+  def up
+    execute <<-SQL
+      CREATE CAST (integer AS text) WITH INOUT AS IMPLICIT;
+    SQL
+    rescue ActiveRecord::StatementInvalid
+  end
+
+  def down
+    execute <<-SQL
+      DROP CAST (integer AS text);
+    SQL
+    rescue ActiveRecord::StatementInvalid
+  end
+end