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Creating an extension
This guide requires an update!
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.
Before we start, let's make sure we have Spree CLI installed by running:
gem install spree_cmd
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
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
def change
add_column :spree_variants, :sale_price, :decimal, precision: 8, scale: 2
end
end
We're not inheriting directly from ActiveRecord::Migration, instead we're using [SpreeExtension::Migration](https://github.com/spree-contrib/spree_extension/blob/master/lib/spree_extension/migration.rb) to support multiple Rails versions.
Before we continue development of our extension, let's add it to the Spree application.
Within the
my_store 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
my_store 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.
bundle exec rails g spree_simple_sales:install
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_simple_sales/spree
Next, create a new file in the directory we just created called
home_controller_decorator.rb and add the following content to it:module SpreeSimpleSales
module Spree
module HomeControllerDecorator
def sale
@products = ::Spree::Product.joins(:variants_including_master).where('spree_variants.sale_price is not null').distinct
end
end
end
end
Spree::HomeController.prepend SpreeSimpleSales::Spree::HomeControllerDecorator
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"
end
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. So, in order to do this, first open up the rails console:bundle exec rails c
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
> variant.save
=> true
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_simple_sales/spree
Next, create the file
app/models/spree_simple_sales/spree/variant_decorator.rb and add the following content to it:module SpreeSimpleSales
module Spree
module VariantDecorator
def price_in(currency)
return super unless sale_price.present?
::Spree::Price.new(variant_id: self.id, amount: self.sale_price, currency: currency)
end
end
end
end
Spree::Variant.prepend SpreeSimpleSales::Spree::VariantDecorator
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 (using return super).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.rbAn 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 = Spree::Price.new(variant_id: variant.id, 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)
end
it "returns the normal price if it is not on sale" do
variant = create(:variant, price: 15.00)
expected = Spree::Price.new(variant_id: variant.id, 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)
end
end
end
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.