Preferences

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We do not advise to use Preferences, we're working on replacing preferences with a more modern solution - https://github.com/spree/spree/issues/11451​
Overview
Spree Preferences support general application configuration and preferences per model instance. Spree comes with preferences for your application like track_inventory_levels. Additional preferences can be added by your application or included extensions.
To implement preferences for a model, simply add a new column called preferences. This is an example migration for the spree_products table:
class AddPreferencesColumnToSpreeProducts < ActiveRecord::Migration[4.2]
  def change
    add_column :spree_products, :preferences, :text
  end
end
This will work because Spree::Product is a subclass of Spree::Base. If found, the preferences attribute gets serialized into a Hash and merged with the default values.
As another example, you might want to add preferences for users to manage their notification settings. Just make sure your User model inherits from Spree::Base then add the preferences column. You'll then be able to define preferences for Users without adding extra columns to the database table.
If you're using spree_auth_devise, note that the provided Spree::User doesn't inherit from Spree::Base.
Extensions may add to the Spree General Settings or create their own namespaced preferences.
The first several sections of this guide describe preferences in a very general way. If you're just interested in making modifications to the existing preferences, you can skip ahead to the Configuring Spree Preferences section. If you would like a more in-depth understanding of the underlying concepts used by the preference system, please read on.
Motivation
Preferences for models within an application are very common. Although the rule of thumb is to keep the number of preferences available to a minimum, sometimes it's necessary if you want users to have optional preferences like disabling e-mail notifications.
Both use cases are handled by Spree Preferences. They are easy to define, provide quick cached reads, persist across restarts and do not require additional columns to be added to your models' tables.
General Settings
Spree comes with many application-wide preferences. They are defined in core/app/models/spree/app_configuration.rb and made available to your code through Spree::Config, e.g., Spree::Config.track_inventory_levels.
A limited set of the general settings are available in the admin interface of your store (/admin/general_settings).
You can add additional preferences under the spree/app_configuration namespace or create your own subclass of Preferences::Configuration.
# These will be saved with key: spree/app_configuration/hot_salsa
Spree::AppConfiguration.class_eval do
  preference :hot_salsa, :boolean
  preference :dark_chocolate, :boolean, default: true
  preference :color, :string
  preference :favorite_number
  preference :language, :string, default: 'English'
end
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# Spree::Config is an instance of Spree::AppConfiguration
Spree::Config.hot_salsa = false
​
# Create your own class
# These will be saved with key: kona/store_configuration/hot_coffee
Kona::StoreConfiguration < Preferences::Configuration
  preference :hot_coffee, :boolean
  preference :color, :string, default: 'black'
end
​
KONA::STORE_CONFIG = Kona::StoreConfiguration.new
puts KONA::STORE_CONFIG.hot_coffee
Defining Preferences
You can define preferences for a model within the model itself:
class User < ActiveRecord::Base
  preference :hot_salsa, :boolean
  preference :dark_chocolate, :boolean, default: true
  preference :color, :string
  preference :favorite_number, :integer
  preference :language, :string, default: "English"
end
In the above model, five preferences have been defined:
hot_salsa
dark_chocolate
color
favorite_number
language
For each preference, a data type is provided. The types available are:
boolean
string
password
integer
text
array
hash
An optional default value may be defined which will be used unless a value has been set for that specific instance.
Accessing Preferences
Once preferences have been defined for a model, they can be accessed either using the shortcut methods that are generated for each preference or the generic methods that are not specific to a particular preference.
Shortcut Methods
There are several shortcut methods that are generated. They are shown below.
Query methods:
user.prefers_hot_salsa? # => false
user.prefers_dark_chocolate? # => false
Reader methods:
user.preferred_color      # => nil
user.preferred_language   # => "English"
Writer methods:
user.prefers_hot_salsa = false         # => false
user.preferred_language = "English"    # => "English"
Check if a preference is available:
user.has_preference? :hot_salsa
Generic Methods
Each shortcut method is essentially a wrapper for the various generic methods shown below:
Query method:
user.prefers?(:hot_salsa)       # => false
user.prefers?(:dark_chocolate)  # => false
Reader methods:
user.preferred(:color)      # => nil
user.preferred(:language)   # => "English"
user.get_preference :color
user.get_preference :language
Writer method:
user.set_preference(:hot_salsa, false)     # => false
user.set_preference(:language, "English")  # => "English"
Accessing All Preferences
You can get a hash of all stored preferences by accessing the preferences helper:
user.preferences # => {"language"=>"English", "color"=>nil}
This hash will contain the value for every preference that has been defined for the model instance, whether the value is the default or one that has been previously stored.
Default and Type
You can access the default value for a preference:
user.preferred_color_default # => 'blue'
Types are used to generate forms or display the preference. You can also get the type defined for a preference:
user.preferred_color_type # => :string
Configuring Spree Preferences
Up until now we've been discussing the general preference system that was adapted to Spree. This has given you a general idea of what types of preference features are theoretically supported. Now, let's start to look specifically at how Spree is using these preferences for configuration.
Reading the Current Preferences
At the heart of Spree preferences lies the Spree::Config constant. This object provides general access to the configuration settings anywhere in the application.
These settings can be accessed from initializers, models, controllers, views, etc.
The Spree::Config constant returns an instance of Spree::AppConfiguration which is where the default values for all of the general Spree preferences are defined.
You can access these preferences directly in code. To see this in action, just fire up rails console and try the following:
>> Spree::Config.admin_products_per_page
=> 10
The above examples show the default configuration values for these preferences. The defaults themselves are coded within the Spree::AppConfiguration class.
class Spree::AppConfiguration < Configuration
  #... snip ...
  preference :allow_guest_checkout, :boolean, default: true
  #... snip ...
end
If you are using the default preferences without any modifications, then nothing will be stored in the database. If you set a value for the preference it will save it to spree_preferences or in our preferences column. It will use a memory cached version to maintain performance.
Overriding the Default Preferences
The default Spree preferences in Spree::AppConfiguration can be changed using the set method of the Spree::Config module. For example to set the number of products shown on the products listing in the admin interface we could do the following:
>> Spree::Config.admin_products_per_page = 20
=> 20
>> Spree::Config.admin_products_per_page
=> 20
Here we are changing a preference to something other than the default as specified in Spree::AppConfiguration. In this case the preference system will persist the new value in the spree_preferences table.
Configuration Through the Spree Initializer
During the Spree installation process, an initializer file is created within your application's source code. The initializer is found under config/initializers/spree.rb:
Spree.config do |config|
  # Example:
  # Uncomment to stop tracking inventory levels in the application
  # config.track_inventory_levels = false
end
The Spree.config block acts as a shortcut to setting Spree::Config multiple times. If you have multiple default preferences you would like to override within your code you may override them here. Using the initializer for setting the defaults is a nice shortcut, and helps keep your preferences organized in a standard location.
For example, if you would like to tax using the shipping address you can accomplish this by doing the following:
Spree.config do |config|
  config.tax_using_ship_address = true
end
Initializing preferences in config/initializers/spree.rb will overwrite any changes that were made through the admin user interface when you restart.
Configuration Through the Admin Interface
The Spree admin interface has several different screens where various settings can be configured. For instance, the admin/general_settings URL in your Spree application can be used to configure the values for the site name and the site URL. This is basically equivalent to calling Spree::Config.set(currency: "CDN", currency_thousands_separator: " ") directly in your Ruby code.
Site-Wide Preferences
You can define preferences that are site-wide and don't apply to a specific instance of a model by creating a configuration file that inherits from Spree::Preferences::Configuration.
class Spree::MyApplicationConfiguration < Spree::Preferences::Configuration
  preference :theme, :string, default: "Default"
  preference :show_splash_page, :boolean
  preference :number_of_articles, :integer
end
In the above configuration file, three preferences have been defined:
theme
show_splash_page
number_of_articles
It is recommended to create the configuration file in the lib/ directory.
Extensions can also define site-wide preferences. For more information on using preferences like this with extensions, check out the Extensions Tutorial.
Configuring Site-Wide Preferences
The recommended way to configure site-wide preferences is through an initializer. Let's take a look at configuring the preferences defined in the previous configuration example.
module Spree
  MyApp::Config = Spree::MyApplicationConfiguration.new
end
​
MyApp::Config[:theme] = "blue_theme"
MyApp::Config[:show_spash_page] = true
MyApp::Config[:number_of_articles] = 5
The MyApp name used here is an example and should be replaced with your actual application's name, found in config/application.rb.
The above example will configure the preferences we defined earlier. Take note of the second line. In order to set and get preferences using MyApp::Config, we must first instantiate the configuration object.
Spree Configuration Options
This section lists all of the configuration options for the current version of Spree.
address_requires_state
Will determine if the state field should appear on the checkout page. Defaults to true.
admin_products_per_page
How many products to display on the products listing in the admin interface. Defaults to 30.
allow_checkout_on_gateway_error
Continues the checkout process even if the payment gateway error failed. Defaults to false.
alternative_shipping_phone
Determines if an alternative phone number should be present for the shipping address on the checkout page. Defaults to false.
A JSON hash of different styles that are supported by attachments. Defaults to:
auto_capture
Depending on whether or not Spree is configured to "auto capture" the credit card, either a purchase or an authorize operation will be performed on the card (via the current credit card gateway). Defaults to false.
company
Determines whether or not a field for "Company" displays on the checkout pages for shipping and billing addresses. Defaults to false.
currency
The three-letter currency code for the currency that prices will be displayed in. Defaults to "USD".
default_country_id
The default country's id. Defaults to 214, as this is the id for the United States within the seed data.
layout
The path to the layout of your application, relative to the app/views directory. Defaults to spree/layouts/spree_application. To make Spree use your application's layout rather than Spree's default, use this:
Spree.config do |config|
  config.layout = "application"
end
max_level_in_taxons_menu
The number of levels to descend when viewing a taxon menu. Defaults to 1.
admin_orders_per_page
The number of orders to display on the orders listing in the admin backend. Defaults to 30.
prices_inc_tax
Determines if prices are labelled as including tax or not. Defaults to false.
shipment_inc_vat
Determines if shipments should include VAT calculations. Defaults to false.
shipping_instructions
Determines if shipping instructions are requested or not when checking out. Defaults to false.
show_descendents
Determines if taxon descendants are shown when showing taxons. Defaults to true.
show_only_complete_orders_by_default
Determines if, on the admin listing screen, only completed orders should be shown. Defaults to true.
show_variant_full_price
Determines if the variant's full price or price difference from a product should be displayed on the product's show page. Defaults to false.
show_store_selector
Display the Store selector in the main nav bar of Storefront and allow users to change Store and Currency. Defaults to false.
tax_using_ship_address
Determines if tax information should be based on shipping address, rather than the billing address. Defaults to true.
track_inventory_levels
Determines if inventory levels should be tracked when products are purchased at checkout. This option causes new InventoryUnit objects to be created when a product is bought. Defaults to true.