migration例子

 1:建表选项
：null => true
:limit=> size
:default => value

ruby 代码

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.column :login, :string
      t.column :email, :string
      t.column :password, :string
      t.column :created_at, :datetime
      t.column :last_login_at, :datetime
      t.column :admin, :boolean
      t.column :posts_count, :integer, :default => 0
    end
  end

  def self.down
    drop_table :users
  end
end

2：添加 字段

ruby 代码

class AddForumDesc < ActiveRecord::Migration
  def self.up
    add_column "forums", "description", :string
  end

  def self.down
    remove_column "forums", "description"
  end
end

3：修改 数据

ruby 代码

class SetLastSeenAt < ActiveRecord::Migration
  def self.up
    User.find(:all).each do |user|
      if user.last_seen_at.nil?
        user.last_seen_at=Time.now.utc
        user.save!
      end
    end
  end

  def self.down
  end
end

4用sql改变 数据

ruby 代码

class FixRepliedAt < ActiveRecord::Migration
  def self.up
    execute 'update posts set replied_at=created_at where replied_at is null and id=topic_id'
  end

  def self.down
  end
end