# StateOfTheNation [![Build Status](https://travis-ci.org/intercom/state_of_the_nation.svg?branch=master)](https://travis-ci.org/intercom/state_of_the_nation) StateOfTheNation helps model data whose _active_ state changes over time. It provides out-of-the-box query methods to locate the record or records active at any moment. Optionally, it also enforces _uniquely_ active constraints at the application level – ensuring that only one record in a collection is active at once. ## Example Take elected officials in the US Government: multiple Senators are in office (i.e. active) at any point in time, but there's only one President. ```ruby class Country < ActiveRecord::Base include StateOfTheNation has_many :presidents has_many :senators has_active :senators has_uniquely_active :president end class President < ActiveRecord::Base belongs_to :country considered_active.from(:entered_office_at).until(:left_office_at) end class Senator < ActiveRecord::Base belongs_to :country considered_active.from(:entered_office_at).until(:left_office_at) end ``` With this collection of models we can easy record and query the list of elected officials at any point in time, and be confident that any new records that we create don't collide. ```ruby usa = Country.create(name: "United States of America") obama = usa.presidents.create!(name: "Barack Obama", entered_office_at: Date.new(2009, 1, 20)) usa.senators.create!(name: "Ron Wyden", entered_office_at: Date.new(1996, 2, 6)) usa.senators.create!(name: "Barbara Boxer", entered_office_at: Date.new(1993, 1, 3)) usa.senators.create!(name: "Alan Cranston", entered_office_at: Date.new(1969, 1, 3), left_office_at: Date.new(1993, 1, 3)) usa.active_president(Date.new(2015)) # => President(id: 1, name: "Barack Obama", …) obama.active? #=> true usa.active_senators(Date.new(2015)) # => [Senator(id: 1, name: "Ron Wyden", …), Senator(id: 2, name: "Barbara Boxer", …)] usa.presidents.create!(name: "Mitt Romney", entered_office_at: Date.new(2013, 1, 20)) # => StateOfTheNation::ConflictError ``` ## IdentityCache Support StateOfTheNation optionally supports fetching records through [IdentityCache](https://github.com/Shopify/identity_cache) instead of reading directly from the database. For example if the `Country` model uses IdentityCache to cache the `has_many` relationship to `President`, you can instruct StateOfTheNation to fetch from the cache by calling `.with_identity_cache` on your `has_active` or `has_uniquely_active` definitions: ```ruby class Country include IdentityCache include StateOfTheNation has_many(:presidents) cache_has_many(:presidents) has_uniquely_active(:president).with_identity_cache end ``` ## Installation Add this line to your application's Gemfile: ```ruby gem 'state_of_the_nation' ``` And then execute: $ bundle Or install it yourself as: $ gem install state_of_the_nation ## Development After checking out the repo, run `bin/setup` to install dependencies. 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](https://rubygems.org). ## Contributing Bug reports and pull requests are welcome on GitHub at https://github.com/intercom/state_of_the_nation. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org/) code of conduct.