How to modify valid exchange items in returns

When customers perform a return, they can be presented with options to exchange the corresponding item. We'll see how we can modify which variants are prompted as eligible.

To begin with, you can go through the checkout process in the storefront and create a completed order. As we need to perform a return, we must capture its payments in the system and mark the shipments as delivered. You can do it in the backend or through the console:

order = Spree::Order.find_by_number('R723438584')
order.payments.map(&:capture!)
order.shipments.map(&:ship!)

If you go now to the backend and try to create a new RMA for that order, you'll see that variants for the same product are shown to the user as valid exchanges. That's because, by default, Spree::ReturnItem::ExchangeVariantEligibility::SameProduct is used as the engine.

Let's be more strict and leverage the default engine to restrict exchanges to those variants of the same product that are not heavier than the original. We need to follow the same API used by the built-in engines.

app/services/amazing_store/return_item/exchange_variant_eligibility/same_product_not_heavier.rb

# frozen_string_literal: true

module AmazingStore
  module ReturnItem
    module ExchangeVariantEligibility
      module SameProductNotHeavier
        def self.eligible_variants(variant, stock_locations: nil)
          Spree::ReturnItem::ExchangeVariantEligibility::SameProduct.
            eligible_variants(variant, stock_locations: stock_locations).
            where(weight: ..variant.weight)
        end
      end
    end
  end
end

Lastly, we need to tell Solidus to use our module by default. We can configure it in the Solidus initializer:

config/initializers/spree.rb

# ...
Rails.application.config.to_prepare do
  ::Spree::ReturnItem.exchange_variant_engine = AmazingStore::ReturnItem::ExchangeVariantEligibility::SameProductNotHeavier
end
# ...

Restart the server and check it out! If you go back to the admin panel, you'll see that only lighter variants are now presented to the user.