change_column で 型を integer や boolean に変更すると失敗する問題の解決方法 ref: http://qiita.com/gam0022/items/a73910de5b8eb44e5b13

file0.txt

[~/RubymineProjects/drwallet]$ rake db:migrate
==  ChangeColumnsToCreditCards: migrating =====================================
-- change_column(:credit_cards, :etc_issuance, :boolean)
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

PG::Error: ERROR:  column "etc_issuance" cannot be cast automatically to type boolean
HINT:  Specify a USING expression to perform the conversion.
: ALTER TABLE "credit_cards" ALTER COLUMN "etc_issuance" TYPE boolean/Users/gam0022/RubymineProjects/drwallet/db/migrate/20150206071431_change_columns_to_credit_cards.rb:3:in `change'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

migration.rb

-change_column :table_name, :column_name, :integer
+change_column :table_name, :column_name, 'integer USING CAST(column_name AS integer)'