rails_console_sandbox

me = User.create(*all the info*)
ruby = Language.create(name: 'ruby')
python = Language.create(name: 'python')

UsersLanguage.add_language(python, me)
=> true 

UsersLanguage.add_language(ruby, me)
=> true 

me.languages.include?(python)
=> true

me.languages.include?(ruby)
=> false

terminal_output

me
=> #<User id: 3, name: "pam", email: "[email protected]", encrypted_password: "$2a$10$Yoow.zTaPTde1zphr88I5OG5YTdUvokXxCEr5UOC0M5...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 0, current_sign_in_at: nil, last_sign_in_at: nil, current_sign_in_ip: nil, last_sign_in_ip: nil, created_at: "2014-09-07 23:32:55", updated_at: "2014-09-07 23:32:55", location: "paris", admin: false>

ruby = Language.create(name: 'ruby')
   (0.2ms)  SAVEPOINT active_record_1
  Language Exists (0.6ms)  SELECT  1 AS one FROM "languages"  WHERE "languages"."name" = 'ruby' LIMIT 1
  SQL (0.4ms)  INSERT INTO "languages" ("created_at", "name", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["created_at", "2014-09-07 23:33:13.571860"], ["name", "ruby"], ["updated_at", "2014-09-07 23:33:13.571860"]]
   (0.2ms)  RELEASE SAVEPOINT active_record_1
=> #<Language id: 5, name: "ruby", created_at: "2014-09-07 23:33:13", updated_at: "2014-09-07 23:33:13">

UsersLanguage.create(user_id: me.id, language_id: ruby.id)
   (0.2ms)  SAVEPOINT active_record_1
  UsersLanguage Exists (0.6ms)  SELECT  1 AS one FROM "users_languages"  WHERE ("users_languages"."language_id" = 5 AND "users_languages"."user_id" = 3) LIMIT 1
  SQL (0.3ms)  INSERT INTO "users_languages" ("created_at", "language_id", "updated_at", "user_id") VALUES ($1, $2, $3, $4) RETURNING "id"  [["created_at", "2014-09-07 23:33:41.210579"], ["language_id", 5], ["updated_at", "2014-09-07 23:33:41.210579"], ["user_id", 3]]
   (0.1ms)  RELEASE SAVEPOINT active_record_1
=> #<UsersLanguage id: 5, user_id: 3, language_id: 5, level: nil, created_at: "2014-09-07 23:33:41", updated_at: "2014-09-07 23:33:41">

me.languages
  Language Load (0.4ms)  SELECT "languages".* FROM "languages" INNER JOIN "users_languages" ON "languages"."id" = "users_languages"."language_id" WHERE "users_languages"."user_id" = $1  [["user_id", 3]]
=> #<ActiveRecord::Associations::CollectionProxy [#<Language id: 5, name: "ruby", created_at: "2014-09-07 23:33:13", updated_at: "2014-09-07 23:33:13">]>


python = Language.create(name: 'python')
   (0.3ms)  SAVEPOINT active_record_1
  Language Exists (0.3ms)  SELECT  1 AS one FROM "languages"  WHERE "languages"."name" = 'python' LIMIT 1
  SQL (0.3ms)  INSERT INTO "languages" ("created_at", "name", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["created_at", "2014-09-07 23:34:12.267952"], ["name", "python"], ["updated_at", "2014-09-07 23:34:12.267952"]]
   (0.2ms)  RELEASE SAVEPOINT active_record_1
=> #<Language id: 6, name: "python", created_at: "2014-09-07 23:34:12", updated_at: "2014-09-07 23:34:12">


UsersLanguage.create(user_id: me.id, language_id: python.id)
   (0.3ms)  SAVEPOINT active_record_1
  UsersLanguage Exists (0.7ms)  SELECT  1 AS one FROM "users_languages"  WHERE ("users_languages"."language_id" = 6 AND "users_languages"."user_id" = 3) LIMIT 1
  SQL (0.5ms)  INSERT INTO "users_languages" ("created_at", "language_id", "updated_at", "user_id") VALUES ($1, $2, $3, $4) RETURNING "id"  [["created_at", "2014-09-07 23:34:19.900723"], ["language_id", 6], ["updated_at", "2014-09-07 23:34:19.900723"], ["user_id", 3]]
   (0.2ms)  RELEASE SAVEPOINT active_record_1
=> #<UsersLanguage id: 6, user_id: 3, language_id: 6, level: nil, created_at: "2014-09-07 23:34:19", updated_at: "2014-09-07 23:34:19">


me.languages
=> #<ActiveRecord::Associations::CollectionProxy [#<Language id: 5, name: "ruby", created_at: "2014-09-07 23:33:13", updated_at: "2014-09-07 23:33:13">]>

users_language.rb

#user.rb

class User < ActiveRecord::Base
  has_many :users_languages
  has_many :languages, through: :users_languages, foreign_key: :user_id
end 

#language.rb

class Language < ActiveRecord::Base
  has_many :users_languages
  has_many :users, through: :users_languages, foreign_key: :language_id
end 

#users_language.rb

class UsersLanguage < ActiveRecord::Base
  belongs_to :user
  belongs_to :language
  
  def self.add_language(language, user) #add the language to the user
  	unless UsersLanguage.exists?(language_id: language.id, user_id: user.id)
  		transaction do 
  			create!(language_id: language.id, user_id: user.id)
  		end
  	else 
  		return 'failed'
  	end
  end
end 

users_language_spec.rb

require 'rails_helper'

describe UsersLanguage do

	let(:user) { FactoryGirl.create(:user) }
	let(:ruby) { FactoryGirl.create(:language) }
	let(:python) { FactoryGirl.create(:language, name: 'Python') }

	describe ".create" do
		context "without a user id" do
			before { UsersLanguage.create }

			it { should_not be_valid }
		end
	end 

	describe ".add_language" do
		before do
		 UsersLanguage.add_language(ruby, user)
		 UsersLanguage.add_language(python, user)
		end 

		it "should add ruby to the user's languages" do
			expect(user.languages).to include(ruby)
		end

		it "should add more than one language to the user's languages" do
			expect(user.languages).to include(python && ruby)
		end
	end
end