module Spree
  class StoreCreditType < ActiveRecord::Base
    DEFAULT_TYPE_NAME = 'Promotional'
    has_one :store_credit, class_name: 'Spree::StoreCredit'
  end
end

module Spree
  class StoreCreditType < ActiveRecord::Base
    DEFAULT_TYPE_NAME = 'Promotional'
    has_many :store_credits, class_name: 'Spree::StoreCredit', foreign_key: 'type_id'
  end
end

Make store credits a has many association on types
Make store credits a has many association on types
