ScopeDelegation

Every application needs to be able to scope data, and every developer hates writing boilerplate code.

With ScopeDelegation, you can easily define scopes in one model that rely on scopes that are defined on an associated model.

Usage

Let's look at an example.

class Whole < ActiveRecord::Base
  extend ScopeDelegation

  has_many :parts

  delegate_scope :named, to: :parts, prefix: :part
end

class Part < ActiveRecord::Base
  belongs_to :whole

  def self.named(name)
    where(name: name)
  end
end

This now enables you to call Whole.part_named("some name") to easily scope your Wholes.

The prefix option is optional, and you can also specify the scope on the associated model if it does not match the first parameter.

Explanation

In a previous life, you might have been tempted to do something like:

# whole.rb
def self.part_named(name)
  joins(:parts).where(name: name)
end

This is unfortunate because now Whole knows about a column name for Part, which is none of its business. Isolating knowledge about the persistence for a given model to that model itself makes changing things easier.

We can get around this with merge, like so:

# whole.rb
def self.part_named(name)
  joins(:parts).merge(Part.named(name))
end

This is what ScopeDelegation does, but with a friendly DSL that allows you to avoid writing boilerplate while discouraging knowing things about your neighbor that you shouldn't.

Installation

Add this line to your application's Gemfile:

gem 'scope_delegation'

And then execute:

$ bundle

Or install it yourself as:

$ gem install scope_delegation

Development

After checking out the repo, run bin/setup to install dependencies. Then, 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 to create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

1. Fork it ( https://github.com/[my-github-username]/scope_delegation/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

About Foraker Labs

Foraker Labs builds exciting web and mobile apps in Boulder, CO. Our work powers a wide variety of businesses with many different needs. We love open source software, and we're proud to contribute where we can. Interested to learn more? Contact us today.

This project is maintained by Foraker Labs. The names and logos of Foraker Labs are fully owned and copyright Foraker Design, LLC.