Question

我是Ruby on Rails的新手，非常感谢有关迁移的一些帮助。第4版

首次迁移

class CreateRooms < ActiveRecord::Migration
  def change
    create_table :rooms do |t|
      t.integer :legacy_id, null: true
      t.string :tag, null: false
      t.string :name_en, null: false
      t.string :name_et, null: false
      t.string :name_ru, null: false
      t.string :color, default: 'Black'
      t.timestamp :enabled_from, default: 0
      t.timestamp :enabled_to, default: 0
      t.timestamps null: false 
    end
    add_index :rooms, :tag, unique: true
    add_index :rooms, :name_en, unique: true
    add_index :rooms, :name_et, unique: true
    add_index :rooms, :name_ru, unique: true

  end
end

下一个

class AddDefaultValuesToRoom < ActiveRecord::Migration
  def change
    add_column :rooms, :priority, :integer, null: false
    change_column :rooms, :enabled_from, :datetime, default: '2008-08-15'
    change_column :rooms, :enabled_to, :datetime, default: '2050-12-31'
    add_index :rooms, :priority, unique: true
  end
end

奇怪的是，这并没有反映在架构中

  create_table "rooms", force: :cascade do |t|
    t.integer  "legacy_id"
    t.string   "tag",                                          null: false
    t.string   "name_en",                                      null: false
    t.string   "name_et",                                      null: false
    t.string   "name_ru",                                      null: false
    t.string   "color",        default: "Black"
    t.datetime "enabled_from", default: '2008-08-15 00:00:00'
    t.datetime "enabled_to",   default: '2050-12-31 00:00:00'
    t.datetime "created_at",                                   null: false
    t.datetime "updated_at",                                   null: false
  end

  add_index "rooms", ["name_en"], name: "index_rooms_on_name_en", unique: true
  add_index "rooms", ["name_et"], name: "index_rooms_on_name_et", unique: true
  add_index "rooms", ["name_ru"], name: "index_rooms_on_name_ru", unique: true
  add_index "rooms", ["tag"], name: "index_rooms_on_tag", unique: true

rake db：rollback崩溃

 rake db:rollback STEP=2 --trace
** Invoke db:rollback (first_time)
** Invoke environment (first_time)
** Execute environment
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:rollback
  ActiveRecord::SchemaMigration Load (0.2ms)  SELECT "schema_migrations".* FROM "schema_migrations"
  ActiveRecord::SchemaMigration Load (0.2ms)  SELECT "schema_migrations".* FROM "schema_migrations"
Migrating to AddDefaultValuesToRoom (20160127121254)
   (0.1ms)  begin transaction
== 20160127121254 AddDefaultValuesToRoom: reverting ===========================
   (0.1ms)  rollback transaction
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

ActiveRecord::IrreversibleMigration/usr/local/rvm/gems/ruby-2.2.1/gems/activerecord-4.2.2/lib/active_record/migration/command_recorder.rb:65:in `inverse_of'

现在我正在解决问题，有人可以帮助我吗？

TIA 帕维尔

Answer 1

change_column会对您的数据库进行不可逆转的更改，这意味着您无法将其回滚。请参阅指南：http://guides.rubyonrails.org/active_record_migrations.html#changing-columns

这里的想法是恢复数据会导致数据丢失，因此Rails会阻止您在默认情况下执行破坏性操作并抛出错误来停止进程。

更改上次迁移以使用reversible或up / down方法，以明确告知Rails如何撤消您的更改（请注意，您将丢失存储在新专栏priority）。请参阅：http://guides.rubyonrails.org/active_record_migrations.html#using-reversible

以下是使用up / down方法的示例：

class AddDefaultValuesToRoom < ActiveRecord::Migration
  def up
    add_column :rooms, :priority, :integer, null: false
    change_column :rooms, :enabled_from, :datetime, default: '2008-08-15'
    change_column :rooms, :enabled_to, :datetime, default: '2050-12-31'
    add_index :rooms, :priority, unique: true
  end

  def down
    remove_column :rooms, :priority
    change_column :rooms, :enabled_from, :datetime, default: 0
    change_column :rooms, :enabled_to, :datetime, default: 0
  end
end

Ruby on Rails迁移陷入困境

1 个答案: