Historio is the gem for recording attribute change histories by terms.

For example, there is a parking space and you want to manage the histories whether it is empty or not.

You can records histories like below:

• The parking space A was empty from 2018-02-20 12:14:30 to 2018-02-20 18:30:00.
• The parking space A was full from 2018-02-20 18:30:00 to 2018-02-21 18:30:00.

Add this line to your application's Gemfile:

gem 'historio'

And then execute:

$ bundle

Or install it yourself as:

$ gem install historio

class ParkingSpace < ActiveRecord::Base
  include Historio::Historizable

  historize
end

In this case, historize creates ParkingSpaceHistory model automatically for recording histories of ParkingSpace.

ParkingSpaceHistory checks the status column by default. So, it is able to record the histories about status changing.

If you want to add some columns to record its changing, you can describe it like below:

class User < ActiveRecord::Base; end

class ParkingSpace < ActiveRecord::Base
  include Historio::Historizable

  historize history_model: ParkingSpaceHistory
end

class ParkingSpaceHistory < ActiveRecord::Bsae
  include Historio::HistoryModel

  watches :status
  watches :user_id
end

In this case, ParkingSpace uses existed ParkingSpaceHistory.

You need to prepare the table on DB for recording history before use.

For example, you can write a migration file on ParkSpaceHistories like below:

class CreateParkSpeceHistories < ActiveRecord::Migration[5.1]
  def change
    create_table :park_space_histories, id: :bigint, unsigned: true do |t|
      t.datetime :first_watched_at, null: false
      t.datetime :last_watched_at, null: false
      t.datetime :last_touched_at, null: false
      t.boolean :latest, null: true

      t.bigint :park_space_id, null: false, unsigned: true
      t.integer :status, null: false, unsigned: true

      t.timestamps
    end
    add_foreign_key :park_space_histories, :park_spaces
    add_index :park_space_histories,
              %i(park_space_id latest),
              unique: true, name: 'index_on_park_space_id_and_latest'
  end
end

There are 2 important parts.

1. defining these columns:

• first_watched_at
• last_watched_at
• last_touched_at
• latest
• primary key on parent model (In this case, park_space_id)

1. adding index on primary key on parent model and latest.

The gem is available as open source under the terms of the MIT License.