ActiveRecord .sorted_where scope

sorted_where.rb

ActiveRecord::Base.class_eval do

  def self.sorted_where(**options)
    # Sort records by the first field given
    sort_field, ordered_values = options.first[0], options.first[1]

    values_and_positions = ordered_values.map.with_index { |id, index| [id, index] }
    positions_by_value = Hash[*values_and_positions.flatten]

    where(**options).to_a.sort_by do |record|
      positions_by_value[record.public_send(sort_field)]
    end
  end

end

sorted_where_spec.rb

require 'spec_helper'

describe ActiveRecord::Base do
  describe '.sorted_where' do
    ALPHABET = ('a'..'z').to_a

    ALPHABET.each do |char|
      let!(char.to_sym) do
        # Works on all ActiveRecord models, Facebook profiles are just an easy example here
        create(:facebook_profile, handle: char)
      end
    end

    it 'returns the records sorted by the first item of the given conditions' do
      sorted_handles = %w[a z y b d f r t s c]
      records = FacebookProfile.sorted_where(handle: sorted_handles)
      records.map(&:handle).should == sorted_handles
    end

    it 'handles records that cannot be found' do
      sorted_handles = %w[a z b MISSING HANDLES c t s]
      expected_handles = %w[a z b c t s]
      records = FacebookProfile.sorted_where(handle: sorted_handles)
      records.map(&:handle).should == expected_handles
    end
  end
end