NumberedRelationships

This gem implements basic filtering of ActiveRecord models on the class and instance level based on the amount of relationships belonging to the object or its associations.

Benefits/ Raison d'Etre

Defining a scope or model method that implements such basic having/count functionality on an ActiveRecord model is trivial:

class Joker << ActiveRecord::Base
	has_many :jokes

	def self.with_at_least_n_jokes(n)
		self.joins(:jokes).group("jokes.id HAVING count(joker_id) >= n")
	end
end

But what if we want to filter a jester's jokes as well? ActiveSupport defines concerns to make module inclusion really simple:

module Humor
	extend ActiveSupport::Concern
	included do
		has_many :jokes
		def with_at_least_n_jokes(n)
			self.joins(:jokes).group("jokes.id HAVING count(joker_id) >= n")
		end
	end
end

class Joker < ActiveRecord::Base
	include Humor
end

Great! We can find the really humurous

Joker.with_at_least_n_jokes(200)

But the following might break, as the hard-coded foreign key "joker_id" might not exist in the jesters table.

class Jester < ActiveRecord::Base
	include Humor
end

The problem is quite clear: the scopes define queries using specific implementation details, making reuse nearly impossible.

But there's also a larger issue here: jokes are only one possible association. If we want the Jester model to include, say, music_instruments -- and to be able to filter on their amount -- we're back at square one, writing another module for each association.

This gem provides relief. Instead of defining modules with hard-coded method names and queries, it uses ActiveRecord's reflection capabilities to enable amount-based filtering on all models and their associations:

# Class-based filters
Joker.with_at_least(2, :music_instruments)
Joker.with_at_least(200, :jokes)

# Instance-based association filters
@first_joker = Joker.find(1)
@first_joker.jokes.with_at_least(10, :tomatoes)

These also call scoped() on all queries and return an instance of ActiveRecord::Relation, meaning that these methods are chainable:

@first_joker.performances.with_at_least(10, :dramatic_moments).where(:duration > 10)

Installation

Add this line to your application's Gemfile:

gem 'numbered_relationships'

And then execute:

$ bundle

Or install it yourself as:

$ gem install numbered_relationships

Usage

This gem extends ActiveRecord, meaning the installation immediately offers the following methods:

Joker.with_at_least(1, :joke)
Joker.with_at_most(2, :jokes)
Joker.with_exactly(2, :jokes)
Joker.without(2, :jokes)
Joker.with_more_than(2, :jokes)
Joker.with_less_than(2, :jokes)

j = Joker.find(123)
j.jokes.with_at_least(1, :laugh)
j.jokes.with_at_most(2, :laughs)
j.jokes.with_exactly(2, :laughs)
j.jokes.without(11, :laughs)
j.jokes.with_more_than(18, :laughs)
j.jokes.with_less_than(2, :laughs)

It's also possible to use class methods or scopes defined on the association class:

Joker.with_at_least(1, [:dirty], :joke)

As long as the class method or scope :dirty is defined on Joker:

class Joke
  def self.dirty
  	where(funny: true)
  end
end

this code will properly filter the results before attempting to group them. It outputs the following SQL:

SELECT jesters.* FROM jesters 
INNER JOIN jokes ON jokes.jester_id = jesters.id 
WHERE jokes.funny = 't' 
GROUP BY jesters.id 
HAVING count(jokes.id) >= 1

These methods, like all other class methods, are chainable, meaning the following would also work:

Joker.with_at_least(1, [:dirty, :insulting, :crying_on_the_floor], :joke)

A call to a non-existent association will -- at least for the moment -- simply return:

[]

TODO:

1. Improve exception handling.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request