Transproc Transformer as ROM Mapper

customers_mapper.rb

module RomInterface
  def self.extended(klass)
    klass.extend ROM::ClassMacros
    klass.defines :relation, :register_as
  end

  def base_relation
    relation
  end

  def build
    new
  end
end

class CustomersMapper < Transproc::Transformer
  extend RomInterface

  relation :customers
  register_as :tuple

  map_array do
    symbolize_keys
    rename_keys user_name: :name
    nest :address, %i(city street zipcode)
    map_value :address do
      constructor_inject Address
    end
    constructor_inject User
  end
end