How to use a custom promotion adjuster

In this guide, we'll see how to create a custom promotion adjuster to use our custom logic that handles promotion adjustments every time an order is updated.

Every time an order is updated, its eligible promotions might not be valid anymore; for example, this could happen if a promotion is tight to a specific order total threshold, and this value changes within the update. In the same way, changing the order could make it eligible for new promotions.

In Solidus, this behavior is encapsulated in the Spree::Promotion::OrderAdjustmentsRecalculator, class, which is called every time the order is updated. This class iterates over all existing promotion adjustments and recalculates their amount and eligibility.

caution

Please, keep in mind that promotion adjustments are handled before taxes are calculated, such that taxes always respect promotions.

We'll now see how to use our own class instead of the one provided by Solidus.

First of all, let's declare which promotion adjuster class we want to use, with the corresponding configuration:

config/initializers/spree.rb

Spree.config do |config|
  # ...
  config.promotion_adjuster_class = 'MyStore::PromotionAdjuster'
end

Next, let's create our custom class, which responds to the same interface of the original promotion adjuster class provided by Solidus:

app/models/my_store/promotion_adjuster.rb

module MyStore
  class PromotionAdjuster
    def initialize(order)
      @order = order
    end

    def call
      # Your custom logic here.
    end
  end
end

info

Keep in mind that if you define your class as:

class PromotionAdjuster < ::Spree::Promotion::OrderAdjustmentsRecalculator

you will be able to use super in its methods to execute parts of the original class provided by Solidus.