blog-migrating-databases-2

blog-migrating-databases-2.rb

class AddColumnUsersIsAdmin < ActiveRecord::Migration
  phase :pre_restart

  def change
    add_column :users, :is_admin, :boolean
  end
end

class BackfillUsersIsAdminNoLock < ActiveRecord::Migration
  phase :post_restart
  disable_ddl_transaction!

  def up
    User.unscoped.find_in_batches(batch_size: batch_size) do |b|
      User.unscoped.where(id: b.map(&:id)).update_all(is_admin: false)
    end
  end

  def down
    User.unscoped.find_in_batches(batch_size: batch_size) do |b|
      User.unscoped.where(id: b.map(&:id)).update_all(is_admin: nil)
    end
  end

  def batch_size
    1000
  end
end

class AddTemporaryIndexUsersIsAdmin < ActiveRecord::Migration
  phase :post_restart
  disable_ddl_transaction!

  def change
    add_index :users, :is_admin, where: 'is_admin IS NULL', algorithm: :concurrently,
      name: 'temp_partial_index_on_users_is_admin'
  end
end

class BackfillUsersIsAdminWithLock < ActiveRecord::Migration
  phase :post_restart

  def up
    execute 'LOCK TABLE users IN ACCESS EXCLUSIVE MODE;'

    User.unscoped.where(is_admin: nil).update_all(is_admin: false)

    change_column_default :users, :is_admin, false
    change_column_null    :users, :is_admin, false
  end

  def down
    change_column_null    :users, :is_admin, true
    change_column_default :users, :is_admin, nil
  end

end

class RemoveTemporaryIndexUsersIsAdmin < ActiveRecord::Migration
  phase :post_restart
  disable_ddl_transaction!

  def up
    remove_index :users, algorithm: :concurrently,
      name: 'temp_partial_index_on_users_is_admin'
  end

  def down
    add_index :users, :is_admin, where: 'is_admin IS NULL', algorithm: :concurrently,
      name: 'temp_partial_index_on_users_is_admin'
  end
end