How to add Spree to an existing Ruby on Rails application with devise authentication

gistfile1.txt

gem 'spree', github: 'spree/spree', :branch => '2-3-stable'
gem 'spree_auth_devise', github: 'spree/spree_auth_devise', branch: '2-3-stable'

$ bundle install

$ rails g spree:install --migrate=false --sample=false --seed=false

config/initializers/spree.rb by changing this line: Spree.user_class = "Spree::User" to this: Spree.user_class = "User"

$ rake spree_auth:install:migrations

$ rails g spree:auth:install

$ rails g spree:custom_user User

$ rake db:migrate

Add this code to user.rb (unless it is already there)

  include Spree::UserReporting
  include Spree::UserApiAuthentication
  has_and_belongs_to_many :spree_roles,
                          :join_table => 'spree_roles_users',
                          :foreign_key => "user_id",
                          :class_name => "Spree::Role"

  has_many :spree_orders, :foreign_key => "user_id", :class_name => "Spree::Order"

  belongs_to :ship_address, :class_name => 'Spree::Address'
  belongs_to :bill_address, :class_name => 'Spree::Address'

  # has_spree_role? simply needs to return true or false whether a user has a role or not.
  def has_spree_role?(role_in_question)
    spree_roles.where(:name => role_in_question.to_s).any?
  end

  def last_incomplete_spree_order
    spree_orders.incomplete.where(:created_by_id => self.id).order('created_at DESC').first
  end

user = [find desired user for admin role]
user.spree_roles << Spree::Role.find_or_create_by(name: "admin")

#routes.rb
mount Spree::Core::Engine, :at => '/spree'

#will_paginate.rb (if using will_paginate gem)
if defined?(WillPaginate)
  module WillPaginate
    module ActiveRecord
      module RelationMethods
        def per(value = nil) per_page(value) end
        def total_count() count end
        def first_page?() self == first end
        def last_page?() self == last end
      end
    end
    module CollectionMethods
      alias_method :num_pages, :total_pages
    end
  end
end