关于rails generate migrate 批改字段类型

关于rails generate migrate 修改字段类型
有几种写法，最早就是add remove了

class AddSsl < ActiveRecord::Migration  def up    add_column :accounts, :ssl_enabled, :boolean, :default => 1  end  def down    remove_column :accounts, :ssl_enabled  endend

rails g migration change_date_format_in_my_tableclass ChangeDateFormatInMyTable < ActiveRecord::Migration  def self.up   change_column :my_table, :my_column, :datetime  end  def self.down   change_column :my_table, :my_column, :date  endend

change_table :table_name do |t|  t.change :column_name, :column_type, {options}endclass ChangeDataTypeForWidgetCount < ActiveRecord::Migration  def self.up    change_table :widgets do |t|      t.change :count, :float    end  end  def self.down    change_table :widgets do |t|      t.change :count, :integer    end  endend

rename_column(table_name, column_name, new_column_name)

add_index(table_name, column_names, options)add_index(:suppliers, :name)#生成CREATE INDEX suppliers_name_index ON suppliers(name)add_index(:accounts, [:branch_id, :party_id], :unique => true)#生成CREATE UNIQUE INDEX accounts_branch_id_party_id_index ON accounts(branch_id, party_id)add_index(:accounts, [:branch_id, :party_id], :unique => true, :name => 'by_branch_party')#生成CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)

class MakeJoinUnique < ActiveRecord::Migration  def up    execute "ALTER TABLE `pages_linked_pages` ADD UNIQUE `page_id_linked_page_id` (`page_id`,`linked_page_id`)"  end  def down    execute "ALTER TABLE `pages_linked_pages` DROP INDEX `page_id_linked_page_id`"  endendclass AddPeopleSalary < ActiveRecord::Migration  def up    add_column :people, :salary, :integer    Person.reset_column_information    Person.find(:all).each do |p|      p.update_attribute :salary, SalaryCalculator.compute(p)    end  endend