Promotions

Overview
Promotions within Spree are used to provide discounts to orders, as well as to add potential additional items at no extra cost. Promotions are one of the most complex areas within Spree, as there are a large number of moving parts to consider. Although this guide will explain Promotions from a developer's perspective, if you are new to this area you can learn a lot from the Admin > Promotions tab where you can set up new Promotions, edit rules & actions, etc.
Promotions can be activated in three different ways:
When a user adds a product to their cart
When a user enters a coupon code during the checkout process
When a user visits a page within the Spree store
Promotions for these individual ways are activated through their corresponding PromotionHandler class, once they've been checked for eligibility.
Promotions relate to two other main components: actions and rules. When a promotion is activated, the actions for the promotion are performed, passing in the payload from the fire_event call that triggered the activator becoming active. Rules are used to determine if a promotion meets certain criteria in order to be applicable.
In some special cases where a promotion has a code or a path configured for it, the promotion will only be activated if the payload's code or path match the promotion's. The code attribute is used for promotion codes, where a user must enter a code to receive the promotion, and the path attribute is used to apply a promotion once a user has visited a specific path.
 Path-based promotions will only work when the `Spree::PromotionHandler::Page` class is used, as in `Spree::ContentController` from `spree_frontend`.
A promotion may also have a usage_limit attribute set, which restricts how many times the promotion can be used.
Actions
There are four actions that come with Spree:
An order-level adjustment
An item-level adjustment
Create line items
Free shipping
Creating an Adjustment
When a CreateAdjustment action is undertaken, an adjustment is automatically applied to the order, unless the promotion has already applied an adjustment to the order.
Once the adjustment has been applied to the order, its eligibility is re-checked every time the order is saved, by way of the Promotion#eligible? method, which uses Promotion#eligible_rules to determine if the promotion is still eligible based on its rules. For how this process works, please see the rules section below.
An adjustment to order from a promotion depends on the calculators. For more information about calculators, please see the Calculators guide.
Creating an item adjustment
When a CreateItemAdjustments action is undertaken, an adjustment is automatically applied to each item within the order unless the action has already been performed on that line item
The eligibility of the item for this promotion is re-checked whenever the item is updated. Its eligibility is based on the rules of the promotion.
An adjustment to order from a promotion depends on the calculators. For more information about calculators, please see the Calculators guide.
Free Shipping
When a FreeShipping action is undertaken, all shipments within the order have their prices negated. Just like with prior actions, the eligibility of this promotion is checked again whenever a shipment changes.
Create Line Items
When a CreateLineItem action is undertaken, a series of line items are automatically added to the order, which may alter the order's price. The promotion with an action to add a line item can also have another action to add an adjustment to the order to nullify the cost of adding the product to the order.
Registering a New Action
You can create a new action for Spree's promotion engine by inheriting from Spree::PromotionAction, like this:
class MyPromotionAction < Spree::PromotionAction
  def perform(options={})
    ...
  end
end
You can access promotion information using the promotion method within any Spree::PromotionAction.
This action must then be registered with Spree, which can be done by adding this code to config/initializers/spree.rb:
Rails.application.config.after_initialize do
  Rails.application.config.spree.promotions.actions << MyPromotionAction
end
Once this has been registered, it will be available within Spree's interface. To provide translations for the interface, you will need to define them within your locale file. For instance, to define English translations for your new promotion action, use this code within config/locales/en.yml:
en:
  spree:
    promotion_action_types:
      my_promotion_action:
        name: My Promotion Action
        description: Performs my promotion action.
Rules
FirstOrder: The user's order is their first.
ItemTotal: The order's total is greater than (or equal to) a given value.
Product: An order contains a specific product.
User The order is by a specific user.
UserLoggedIn: The user is logged in.
One Use Per User: Can be used only once per customer.
Taxon(s): Order includes product(s) with taxons that you associate to this rule.
Country: Ship Address country used for this Order matches the selected Country, eg. US-only Orders
Rules are used by Spree to determine if a promotion is applicable to an order and can be matched in one of two ways: all of the rules must match, or one rule must match. This is determined by the match_policy attribute on the Promotion object. As you will see in the Admin, you can set the match_policy to be "any" or "all" of the rules associated with the Promotion. When set to "any" the Promotion will be considered eligible if any one of the rules applies, when set to "all" it will be eligible only if all the rules apply.
Registering a New Rule
As a developer, you can create and register a new rule for your Spree app with custom business logic specific to your needs. First, define a class that inherits from Spree::PromotionRule, like this:
module Spree
  class Promotion
    module Rules
      class MyPromotionRule < Spree::PromotionRule
        def applicable?(promotable)
          promotable.is_a?(Spree::Order)
        end
​
        def eligible?(order, options = {})
          ...
        end
​
        def actionable?(line_item)
          ...
        end
      end
    end
  end
end
The eligible? method should then return true or false to indicate if the promotion should be eligible for an order. You can retrieve promotion information by calling promotion.
If your promotion supports some giving discounts on some line items, but not others, you should define actionable? to return true if the specified line item meets the criteria for promotion. It should return true or false to indicate if this line item can have a line item adjustment carried out on it.
For example, if you are giving a promotion on specific products only, eligible? should return true if the order contains one of the products eligible for promotion, and actionable? should return true when the line item specified is one of the specific products for this promotion.
You can then register the promotion using this code inside config/initializers/spree.rb:
Rails.application.config.spree.promotions.rules << Spree::Promotion::Rules::MyPromotionRule
 Proper location and file name for the rule in this example would be: app/models/spree/promotion/rules/my_promotion_rule.rb
To get your rule to appear in the admin promotions interface you have a few more changes to make.
Create a partial for your new rule in app/views/spree/admin/promotions/rules/_my_promotion_rule.html.erb.
This file can be as simple as an empty file if your rule requires no parameters, or it may require more complex markup to enable setting values for your new rule. Check out some of the rule partials provided with Spree in the backend sources.
And finally, your new rule must have a name and description defined for the locale you will be using it in. For English, edit config/locales/en.yml and add the following to support our new example rule:
en:
  spree:
    promotion_rule_types:
      my_promotion_rule:
        name: "My Promotion Rule"
        description: "Rule to define my new promotion"
Restart your application. Once this rule has been registered, it will be available within Spree's admin interface.

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Outline

Overview

Actions

Creating an Adjustment

Creating an item adjustment

Free Shipping

Create Line Items

Registering a New Action

Rules

Registering a New Rule