This tutorial continues where we left off in the Getting Started tutorial. Now that we have a basic Spree store up and running, let’s spend some time customizing it. The easiest way to do this is by using Spree extensions.

What is a Spree Extension?

Extensions are the primary mechanism for customizing a Spree site. They provide a convenient mechanism for Spree developers to share reusable code with one another. Even if you do not plan on sharing your extensions with the community, they can still be a useful way to reuse code within your organization. Extensions are also a convenient mechanism for organizing and isolating discrete chunks of functionality.

Installing an Extension

We are going to be adding the spree_i18n extension to our store. SpreeI18n is a extension containing community contributed translations of Spree & ability to supply different attribute values per language such as product names and descriptions. Extensions can also add models, controllers, and views to create new functionality.

There are three steps we need to take to install spree_i18n.

First, we need to add the gem to the bottom of our Gemfile:

gem 'spree_i18n', github: 'spree-contrib/spree_i18n', branch: 'master'

If you are using a 3.0.x or 2.x version of Spree, you’ll need to change the branch to X-X-stable to match the version of Spree you’re using. For example, use 3-0-stable if you’re using Spree 3.0.x.

Now, let’s install the gem via Bundler with the following command:

$ bundle install

Finally, let’s copy over the required migrations and assets from the extension with the following command:

$ bundle exec rails g spree_i18n:install

Answer yes when prompted to run migrations.

Creating an Extension

Getting Started

Let’s build a simple extension. Suppose we want the ability to mark certain products as being on sale. We’d like to be able to set a sale price on a product and show products that are on sale on a separate products page. This is a great example of how an extension can be used to build on the solid Spree foundation.

So let’s start by generating the extension. Run the following command from a directory of your choice outside of our Spree application:

$ spree extension simple_sales

This creates a spree_simple_sales directory with several additional files and directories. After generating the extension make sure you change to its directory:

$ cd spree_simple_sales

Adding a Sale Price to Variants

The first thing we need to do is create a migration that adds a sale_price column to variants.

We can do this with the following command:

bundle exec rails g migration add_sale_price_to_spree_variants sale_price:decimal

Because we are dealing with prices, we need to now edit the generated migration to ensure the correct precision and scale. Edit the file db/migrate/XXXXXXXXXXX_add_sale_price_to_spree_variants.rb so that it contains the following:

class AddSalePriceToSpreeVariants < SpreeExtension::Migration[4.2]
  def change
    add_column :spree_variants, :sale_price, :decimal, precision: 8, scale: 2

We’re not inheriting directly from ActiveRecord::Migration, instead we’re using SpreeExtension::Migration to support multiple Rails versions.

Adding Our Extension to the Spree Application

Before we continue development of our extension, let’s add it to the Spree application we created in the last tutorial. This will allow us to see how the extension works with an actual Spree store while we develop it.

Within the mystore application directory, add the following line to the bottom of our Gemfile:

gem 'spree_simple_sales', path: '../spree_simple_sales'

You may have to adjust the path somewhat depending on where you created the extension. You want this to be the path relative to the location of the mystore application.

Once you have added the gem, it’s time to bundle:

$ bundle install

Finally, let’s run the spree_simple_sales install generator to copy over the migration we just created (answer yes if prompted to run migrations):

# context: Your Spree store's app root (i.e. Rails.root); not the extension's root path.
$ rails g spree_simple_sales:install

Adding a Controller Action to HomeController

Now we need to extend Spree::HomeController and add an action that selects “on sale” products.

Note for the sake of this example that Spree::HomeController is only included in spree_frontend so you need to make it a dependency on your extensions *.gemspec file.

Make sure you are in the spree_simple_sales root directory and run the following command to create the directory structure for our controller decorator:

$ mkdir -p app/controllers/spree

Next, create a new file in the directory we just created called home_controller_decorator.rb and add the following content to it:

Spree::HomeController.class_eval do
  def sale
    @products = Spree::Product.joins(:variants_including_master).where('spree_variants.sale_price is not null').distinct

This will select just the products that have a variant with a sale_price set.

We also need to add a route to this action in our config/routes.rb file. Let’s do this now. Update the routes file to contain the following:

Spree::Core::Engine.routes.draw do
  get "/sale" => "home#sale"

Viewing On Sale Products

Setting the Sale Price for a Variant

Now that our variants have the attribute sale_price available to them, let’s update the sample data so we have at least one product that is on sale in our application. We will need to do this in the rails console for the time being, as we have no admin interface to set sale prices for variants. We will be adding this functionality in the next tutorial in this series, Deface overrides.

So, in order to do this, first open up the rails console:

$ rails console

Now, follow the steps I take in selecting a product and updating its master variant to have a sale price. Note, you may not be editing the exact same product as I am, but this is not important. We just need one “on sale” product to display on the sales page.

> product = Spree::Product.first
=> #<Spree::Product id: 107377505, name: "Spree Bag", description: "Lorem ipsum dolor sit amet, consectetuer adipiscing...", available_on: "2013-02-13 18:30:16", deleted_at: nil, permalink: "spree-bag", meta_description: nil, meta_keywords: nil, tax_category_id: 25484906, shipping_category_id: nil, count_on_hand: 10, created_at: "2013-02-13 18:30:16", updated_at: "2013-02-13 18:30:16", on_demand: false>

> variant = product.master
=> #<Spree::Variant id: 833839126, sku: "SPR-00012", weight: nil, height: nil, width: nil, depth: nil, deleted_at: nil, is_master: true, product_id: 107377505, count_on_hand: 10, cost_price: #<BigDecimal:7f8dda5eebf0,'0.21E2',9(36)>, position: nil, lock_version: 0, on_demand: false, cost_currency: nil, sale_price: nil>

> variant.sale_price = 8.00
=> 8.0

=> true

Creating a View

Now we have at least one product in our database that is on sale. Let’s create a view to display these products.

First, create the required views directory with the following command:

$ mkdir -p app/views/spree/home

Next, create the file app/views/spree/home/sale.html.erb and add the following content to it:

<div data-hook="homepage_products">
  <%= render 'spree/shared/products', products: @products %>

If you navigate to http://localhost:3000/sale you should now see the product(s) listed that we set a sale_price on earlier in the tutorial. However, if you look at the price, you’ll notice that it’s not actually displaying the correct price. This is easy enough to fix and we will cover that in the next section.

Decorating Variants

Let’s fix our extension so that it uses the sale_price when it is present.

First, create the required directory structure for our new decorator:

$ mkdir -p app/models/spree

Next, create the file app/models/spree/variant_decorator.rb and add the following content to it:

Spree::Variant.class_eval do
  alias_method :orig_price_in, :price_in
  def price_in(currency)
    return orig_price_in(currency) unless sale_price.present?, amount: self.sale_price, currency: currency)

Here we alias the original method price_in to orig_price_in and override it. If there is a sale_price present on the product’s master variant, we return that price. Otherwise, we call the original implementation of price_in.

Testing Our Decorator

It’s always a good idea to test your code. We should be extra careful to write tests for our Variant decorator since we are modifying core Spree functionality. Let’s write a couple of simple unit tests for variant_decorator.rb

Generating the Test App

An extension is not a full Rails application, so we need something to test our extension against. By running the Spree test_app rake task, we can generate a barebones Spree application within our spec directory to run our tests against.

We can do this with the following command from the root directory of our extension:

$ bundle exec rake test_app

After this command completes, you should be able to run rspec and see the following output:

No examples found.

Finished in 0.00005 seconds
0 examples, 0 failures

Great! We’re ready to start adding some tests. Let’s replicate the extension’s directory structure in our spec directory by running the following command

$ mkdir -p spec/models/spree

Now, let’s create a new file in this directory called variant_decorator_spec.rb and add the following tests to it:

require 'spec_helper'

describe Spree::Variant do
  describe "#price_in" do
    it "returns the sale price if it is present" do
      variant = create(:variant, sale_price: 8.00)
      expected =, currency: "USD", amount: variant.sale_price)

      result = variant.price_in("USD")

      expect(result.variant_id).to eq(expected.variant_id)
      expect(result.amount.to_f).to eq(expected.amount.to_f)
      expect(result.currency).to eq(expected.currency)

    it "returns the normal price if it is not on sale" do
      variant = create(:variant, price: 15.00)
      expected =, currency: "USD", amount: variant.price)

      result = variant.price_in("USD")

      expect(result.variant_id).to eq(expected.variant_id)
      expect(result.amount.to_f).to eq(expected.amount.to_f)
      expect(result.currency).to eq(expected.currency)

These specs test that the price_in method we overrode in our VariantDecorator returns the correct price both when the sale price is present and when it is not.


In this tutorial you learned how to both install extensions and create your own. A lot of core Spree development concepts were covered and you gained exposure to some of the Spree internals.

In the next part of this tutorial series, we will cover Deface overrides and look at ways to improve our current extension.