# Pastebin bG9ABlAS
    class AssociationOperation
      attr_reader :model_mapper, :mapper_registry, :model, :attributes,
                  :options
      def initialize(
          model_mapper,
          mapper_registry,
          model,
          attributes,
          **options)
        @model_mapper    = model_mapper
        @mapper_registry = mapper_registry
        @model           = model
        @attributes      = attributes
        @options         = options
      end

      def finish
        # NOOP
      end

      def mapper_for_class(klass)
        mapper_registry.fetch(klass)
      end
    end

    class AssociationStoreOperation < AssociationOperation
      def belongs_to(association_class, field, column, inverse_of: nil)
        mapper = mapper_for_class(association_class)
        object = model.public_send(field)
        if inverse_of
          object.public_send("#{inverse_of}=", model)
        end
        attributes[column] = object.id
        mapper.store(object)
      end

      def has_one(association_class, field, column)
        # NOOP
      end
    end

    class AssociationLoadOperation < AssociationOperation
      def belongs_to(association_class, field, column, inverse_of: nil)
        mapper    = mapper_for_class(association_class)
        object_id = attributes.delete(column)
        object    = mapper.find(object_id)
        model.public_send("#{field}=", object)
      end

      def has_one(association_class, field, column)
        mapper = mapper_for_class(association_class)
        if object = mapper.public_send("find_by_#{column}", column)
          model.public_send("#{field}=", object)
        end
      end
    end