我運行:默認值
軌產生遷移AddHidemsgColumnToPublishers hide_msg:布爾
和下一個文件的創建:
class AddHidemsgColumnToPublishers < ActiveRecord::Migration
def change
add_column :publishers, :hide_msg, :boolean
end
end
我想設置一個默認值到hide_msg
由虛假。
所以我嘗試:
軌產生遷移add_default_value_to_hide_msg
class AddDefaultValueToHideMsg < ActiveRecord::Migration
def up
change_column :publishers, :hide_msg, :boolean, :default => false
end
def down
change_column :publishers, :hide_msg, :boolean, :default => nil
end
end
,但我得到的錯誤:
rake db:migrate
== AddHidemsgColumnToPublishers: migrating ===================================
-- add_column(:publishers, :hide_msg, :boolean, {:default=>false})
rake aborted!
An error has occurred, this and all later migrations canceled:
PG::Error: ERROR: column "hide_msg" of relation "publishers" already exists
: ALTER TABLE "publishers" ADD COLUMN "hide_msg" boolean DEFAULT 'f'
謝謝您的解釋! –