参考资料

数据库迁移

Creating a Migration

  • Create a Standalone Migration

    $ rails generate migration AddModeToStandardLogs mode:string

    invoke  active_record
create    db/migrate/20120813055814_add_mode_to_standard_logs.rb

    $ rails generate migration AddModeToInfoLogs mode:string

    /db/migrate/20120813055814_add_mode_to_standard_logs.rb

    class AddModeToStandardLogs < ActiveRecord::Migration
  def self.up
    add_column :standard_logs, :mode, :string
  end

  def self.down
    remove_column :standard_logs, :mode
  end
end

  • Create a Standalone Migration with more columns.

    $ rails generate migration AddDetailsToInfoLogs device_type:string phase:string completion:string

  • Set default value.

change the created migration

   def self.up
     add_column :info_logs, :mode, :string, :default => "uploading"
   end

Running Migrations

$ rake db:migrate VERSION=20120813055814

$ rake db:migrate VERSION=20120813075400

Rolling Back

$ rake db:rollback

This will run the down method from the latest migration. If you need to undo several migrations you can provide a STEP parameter:

$ rake db:rollback STEP=3

will run the down method from the last 3 migrations.

The db:migrate:redo task is a shortcut for doing a rollback and then migrating back up again. As with the db:rollback task, you can use the STEP parameter if you need to go more than one version back, for example

$ rake db:migrate:redo STEP=3