Spree and Software Development: Git and Ruby techniques
March 31, 2010
Having tackled a few interesting Spree projects lately, I thought I’d share some software evelopment tips I’ve picked up along the way.
Gem or Source?
The first decision you may need to make is whether to run Spree from a gem or source. Directions for both are included at the Spree Quickstart Guide, but the guide doesn’t touch on motivation from running from a gem versus source. The Spree documentation does address the question, but I wanted to comment based on recent experience. I’ve preferred to build an application running from the gem for most client projects. The only times I’ve decided to work against Spree source code was when the Spree edge code had a major change that wasn’t available in a released gem, or if I wanted to troubleshoot the internals of Spree, such as the extension loader or localization functionality.
If you follow good code organization practices and develop modular and abstracted functionality, it should be quite easy to switch back and forth between gem and source. However, switching back and forth between Spree gem and source may not be cleanly managed from a version control perspective.
Git rebase is lovely. Ethan describes some examples of using git rebase here. When working with several other developers and even when I’m the sole developer, I’ve included rebasing in my pull and push workflow.
Git submodules are lovely, also. An overview on git submodules with contributions from Brian Miller and David Christensen can be read here. Below is an example of a .gitmodules from a recent project that includes several extensions written by folks in the Spree community:
[submodule "vendor/extensions/faq"] path = vendor/extensions/faq url = git://github.com/joshnuss/spree-faq.git [submodule "vendor/extensions/multi_domain"] path = vendor/extensions/multi_domain url = git://github.com/railsdog/spree-multi-domain.git [submodule "vendor/extensions/paypal_express"] path = vendor/extensions/paypal_express url = git://github.com/railsdog/spree-paypal-express.git
Overriding modules, controllers, and views
Now, the good stuff! So, let’s assume the Spree core is missing functionality that you need. Options for expanding from the Spree core include overriding or extending existing models, controllers, or views, or writing and including new models, controllers, or views. Spree’s Extension Tutorial covers adding new controllers, models, and views, so I’ll discuss extending and overriding existing models, views and controllers below.
Extend an Existing Controller
To extend an existing controller, I’ve typically included a module with the extended behavior in the *_extension.rb file. For all examples, let’s assume that my extension is named "Site", another standard in Spree. The code below shows the module include in site_extension.rb:
... def activate ProductsController.send(:include, Spree::Site::ProductsController) end ...
My ProductsController module, inside the Spree::Site namespace, includes the following to define a before filter in the Spree core products controller:
module Spree::Site::ProductsController def self.included(controller) controller.class_eval do controller.append_before_filter :do_stuff end end def do_stuff #doing stuff end end
Override an Existing Controller Method
Next, to override a method in an existing controller, I’ve started the same way as before, by including a module in site_extension.rb:
... def activate CheckoutsController.send(:include, Spree::Site::CheckoutsController) end ...
The Spree::Site::CheckoutsController module will contain:
module Spree::Site::CheckoutsController def self.included(target) target.class_eval do alias :spree_rate_hash :rate_hash def rate_hash; site_rate_hash; end end end def site_rate_hash # compute new rate_hash end end
In this example, the core rate_hash method is aliased for later use. And the rate_hash method is redefined inside the class_eval block. This example demonstrates how to override the core shipping rate computation during checkout.
Extend an Existing Model
Next, I’ll provide an example of extending an existing Spree model. site_extension.rb will include the following:
... def activate Product.send(:include, Spree::Site::Product) end ...
And Spree::Site::Product module contains:
module Spree::Site::Product def new_product_method # new product instance method end end
In the situation where you may want to create a class object method rather than an instance object method, you may include the following in Spree::Site::Product:
module Spree::Site::Product def self.included(target) def target.do_something_special 'Something Special!' end end end
The above example adds a method to the Product class object to be called from a view, for example <%= Product.do_something_special %> will return ‘Something Special!’.
Override an Existing Model Method
To override a method from an existing model, I start with a module include in site_extension.rb:
... def activate Product.send(:include, Spree::Site::Product) end ...
And Spree::Site::Product contains the following:
module Spree::Site::Product def self.included(model) model.class_eval do alias :spree_master_price :master_price def master_price; site_master_price; end end end def site_master_price '1 billion dollars' end end
And from the view, the two methods can be called within the following block:
<% @products.each do |product| -%> <%= product.master_price %> vs <%= product.spree_master_price.to_s %> <% end -%>
Extend an Existing View
I previously discussed the introduction of hooks in depth here and here. To extend an existing view that has a hook wrapped around the content you intend to modify, you may add something similar to the following to *_hooks.rb, where * is the extension name:
insert_after :homepage_products, 'shared/promo'
The above code inserts the ‘shared/promo’ view to be rendered above the homepage_products hook in the Spree gem or Spree source ~/app/views/products.index.html.erb view. Other hook actions include insert_before, replace, or remove.
Override an Existing View
Before the introduction of hooks, the standard method of overriding or extending core views was to copy the core view into your extension view directory, and apply changes. In some cases, hooks are not always in the desired location. To override the footer view since there is no footer hook, I copy the Spree gem footer view to the extension view directory. The diff below compares the Spree gem view and my extension footer view:
- <div id="footer"> - <div class="left"> - <p> - <%= t("powered_by") %> <a href="http://spreecommerce.com/">Spree</a> - </p> - </div> - <div class="right"> - <%= render 'shared/language_bar' if Spree::Config[:allow_locale_switching] %> - </div> - </div> <%= render 'shared/google_analytics' %> + <p><a href="http://www.endpoint.com/">End Point</a></p>
A final tip that I’ve found helpful when developing with Spree is to create sample data files in the extension db directory to maintain data consistency between developers. In a recent project, I’ve created the following stores.yml data to initiate several stores for the multi domain extension:
store_1: name: Store1 code: store1 domains: store1.mysite.com default: false store_2: name: Store2 code: store2 domains: store2.mysite.com default: true store_3: name: Store3 code: store3 domains: store3.mysite.com default: false
Many of these tips apply to general to software development. The tips specific to development in Spree (and possibly other Rails platforms) include the sample data syntax and the described Ruby techniques to extend and override class and model functionality.