Integrating Paypal Express with Rails 3.1, Part 1

Ever wanted to add this button to your site?

I spent a few weeks figuring out how to make the Paypal checkout button work properly on my site. There were a lot of resources on the web, but none of them were complete. After a lot of trial and error, here is the step-by-step guide that should provide everything you need.

Adding the Paypal Button to Your Site

The first step is the simplest one: add the button to your site!

Find the page on your site where you want to add the button, and paste the following code to add a clickable Paypal checkout button. Please note that I use Haml for my project.

= link_to image_tag("https://www.paypal.com/en_US/i/btn/btn_xpressCheckout.gif"), :controller => 'paypal_express', :action => 'checkout'

You will notice that I have a controller called ‘PaypalExpress’ with a custom action called ‘checkout’. We don’t have such controller yet, but at least you have a button on your site now.

Modifying Rails routes.rb

Try using Firebug to inspect the Paypal checkout button. You will notice that the href is ‘paypal_express/checkout’. So, to make the link work properly when we click on it, we need to add the following line to routes.rb:

  get "paypal_express/checkout"

Of course, clicking on it will make Rails complain that such controller doesn’t exist. So now it’s time to create the controller.

Creating PaypalExpressController

Here’s what my PaypalExpressController looks like:

class PaypalExpressController < ApplicationController
  before_filter :assigns_gateway

  include ActiveMerchant::Billing
  include PaypalExpressHelper

  def checkout
    total_as_cents, setup_purchase_params = get_setup_purchase_params @cart, request
    setup_response = @gateway.setup_purchase(total_as_cents, setup_purchase_params)
    redirect_to @gateway.redirect_url_for(setup_response.token)
  end

  private
    def assigns_gateway
      @gateway ||= PaypalExpressGateway.new(
        :login => PaypalLogin.login,
        :password => PaypalLogin.password,
        :signature => PaypalLogin.signature,
      )
    end
end

There are quite a few ivars/classes/modules/methods used in the controller, namely:

• ActiveMerchant::Billing and PaypalExpressGateway
• PaypalLogin
• PaypalExpressHelper and get_setup_purchase_params method
• @cart

A lot of code right? No worries. I will go over the details you need to know. Before we dive into the details of what the controller does, let’s take care of all the dependencies I just mentioned.

gem 'activemerchant'

YourApp::Application.configure do

  # Some other stuff in development.rb
  
  # Force ActiveMerchant into test mode
  config.after_initialize do
    ActiveMerchant::Billing::Base.mode = :test
  end
end

{
  :login => "seller_1229899173_biz_api1.railscasts.com",
  :password => "FXWU58S7KXFC6HBE",
  :signature => "AGjv6SW.mTiKxtkm6L9DcSUCUgePAUDQ3L-kTdszkPG8mRfjaRZDYtSu"
}

module PaypalExpressHelper
  def get_setup_purchase_params(cart, request)
    subtotal, shipping, total = get_totals(cart)
    return to_cents(total), {
      :ip => request.remote_ip,
      :return_url => url_for(:action => 'review', :only_path => false),
      :cancel_return_url => home_url,
      :subtotal => to_cents(subtotal),
      :shipping => to_cents(shipping),
      :handling => 0,
      :tax =>      0,
      :allow_note =>  true,
      :items => get_items(cart),
    }
  end

  def get_shipping(cart)
    # define your own shipping rule based on your cart here
    # this method should return an integer
  end

  def get_items(cart)
    cart.line_items.collect do |line_item|
      product = line_item.product

      {
        :name => product.title, 
        :number => product.serial_number, 
        :quantity => line_item.quantity, 
        :amount => to_cents(product.price), 
      }
    end
  end

  def get_totals(cart)
    subtotal = cart.subtotal
    shipping = get_shipping(cart)
    total = subtotal + shipping
    return subtotal, shipping, total
  end

  def to_cents(money)
    (money*100).round
  end
end

:ip => request.remote_ip,
:return_url => url_for(:action => 'review', :only_path => false),
:cancel_return_url => home_url,