https://github.com/intercom/state_of_the_nation
An easy way to model state changing over time with ActiveRecord.
https://github.com/intercom/state_of_the_nation
Last synced: 10 months ago
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An easy way to model state changing over time with ActiveRecord.
- Host: GitHub
- URL: https://github.com/intercom/state_of_the_nation
- Owner: intercom
- License: apache-2.0
- Created: 2016-01-05T13:53:53.000Z (about 10 years ago)
- Default Branch: master
- Last Pushed: 2023-08-01T02:23:00.000Z (over 2 years ago)
- Last Synced: 2025-04-12T06:43:21.798Z (10 months ago)
- Language: Ruby
- Homepage:
- Size: 60.5 KB
- Stars: 25
- Watchers: 145
- Forks: 6
- Open Issues: 7
-
Metadata Files:
- Readme: README.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
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README
# StateOfTheNation
[](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.