Ruby on Rails migration stuck - ruby-on-rails-4

Question

I'm new to Ruby on Rails and would be grateful for some help with migrations.
Version 4
first migration
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
next one
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
Strangely enough this is not reflected in schema
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 crashes
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'
Now I'm in a fix, could somebody help me out ?
TIA
Pavel

Answer 1

change_column creates an irreversible change to your database, which means you can't roll it back. See the guide: http://guides.rubyonrails.org/active_record_migrations.html#changing-columns
The idea here is that reverting your data would result in data loss, so Rails prevents you from doing something destructive by default and throws an error to stop the process.
Change your last migration to utilize reversible or up/down methods, in order to explicitly tell Rails how to reverse your change (note that you will lose any data stored in the new column priority). See: http://guides.rubyonrails.org/active_record_migrations.html#using-reversible
Here's an example using up/down methods:
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