In-memory Arel

in_memory_arel_spec.rb

# require 'spec_helper'

class InMemoryArel
  attr_accessor :collection

  def initialize(collection)
    self.collection = collection
  end

  def all
    collection
  end

  def where(conditions)
    _where(collection, conditions)
  end

private

  def _where(working_collection, conditions)
    conditions.each do |key, value|
      working_collection = _where_key_matches(working_collection, key, value)
      break if working_collection.empty?
    end
    working_collection
  end

  def _where_key_matches(working_collection, key, value)
    working_collection.select do |e|
      e.public_send(key) == value
    end
  end
end

describe InMemoryArel do
  MySpecialClass = Struct.new(:id, :name, :category, :color)

  let(:collection) do
    [
      {id: 1, name: "Apple", category: "fruit", color: "red"},
      {id: 2, name: "Banana", category: "fruit", color: "yellow"},
      {id: 3, name: "Pear", category: "fruit", color: "green"},
      {id: 4, name: "Grape", category: "fruit", color: "green"},
      {id: 5, name: "Orange", category: "fruit", color: "orange"},
      {id: 6, name: "Pineapple", category: "fruit", color: "yellow"},
      {id: 7, name: "Broccoli", category: "vegetable", color: "green"},
      {id: 8, name: "Carrot", category: "vegetable", color: "orange"},
      {id: 9, name: "Green Beans", category: "vegetable", color: "green"},
      {id: 10, name: "Kale", category: "vegetable", color: "green"},
      {id: 11, name: "Peas", category: "vegetable", color: "green"},
      {id: 12, name: "Mac", category: "computer", color: "silver"},
      {id: 13, name: "PC", category: "computer", color: "beige"},
    ].map do |h|
      MySpecialClass.new(h[:id], h[:name], h[:category], h[:color])
    end
  end
  subject(:arel) { InMemoryArel.new(collection) }

  describe "#all" do
    it "returns the collection" do
      expect(arel.all).to eq collection
    end
  end

  describe "#where" do
    it "returns elements that match the given key" do
      expect(arel.where(category: "computer").map(&:name)).to eq %w(Mac PC)
    end

    it "reduces results based on additional conditions" do
      expect(arel.where(category: "fruit", color: "green").map(&:name)).to eq %w(Pear Grape)
    end
  end
end