Object State

This gem helps to encapsulate state of objects of (typically) Ruby on Rails applications.

• The state becomes easy to identify in the source code.
• There is a standard method for converting the state to and from query params.
• The state can be expressed in the form of a cache_key.
• It is possible to additionally typecast and/or validate its attributes.

Useful for pagination, filtering etc.

Add this line to your application's Gemfile:

gem 'object_state'

And then execute:

$ bundle

Or install it yourself as:

$ gem install object_state

class MyObj
  include ObjectState::Owner

  object_state do
    attr_accessor :current_date
  end
end

my_obj.to_object_state_hash # => { my_obj => { id: "123", current_date: "2016-08-27" } }

This hash can be easily used as query params, for example:

my_obj_path(my_obj, my_obj.to_object_state_hash)

An attribute can be easily overridden:

my_obj_path(my_obj, my_obj.to_object_state_hash(current_date: Date.tomorow))

my_obj.assign_attributes_from_object_state_hash(…)

The attributes will be assigned only if the id in the state hash matches the id of your object. This is helpful for example when used in controllers.

• PoRo (attr_accessor)
• Mongoid fields
• Virtus attributes

Optionally the state can be processed by a custom class. This is useful when the values need to be typecast, validated, or transformed. The ObjectState::State includes ActiveModel::Model and Virtus so you can use Virtus' attribute definition and ActiveModel validations. For example:

class MyObj::State < ObjectState::State
  attribute :current_date, Date

  validates :current_date, inclusion: { in: Date.today..Date.tomorrow }, presence: true
end

Only valid values will be assigned to your object.

class MyObj
  include ObjectState::Owner

  object_state class_name: 'MyObj::State' do
    attr_accessor :current_date
  end
end

Often values or views associated with the object need to be cached (and the cache expired) depending on its state. The :object_state_cache_key generates a cache key based on the state's values. For example the MyObj from the above example:

my_obj.object_state_cache_key # => '2016-08-27'

In fact the object_state method automatically merges the state object's cache key with the object's cache_key:

my_obj.cache_key # => '<object-cache-key>/2016-08-27'

This can be disabled as follows:

class MyObj
  include ObjectState::Owner

  object_state merge_cache_key: false do
    attr_accessor :current_date
  end
end

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/tomasc/object_state.

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