ROM self-referential associations with views

gistfile1.txt

# frozen_string_literal: true

require 'types'

module Persistence
  module Relations
    # Relation for the +regions+ table.
    class Regions < ROM::Relation[:sql]
      schema(:regions) do
        attribute :id, Types::Int
        attribute :country_id, Types::ForeignKey(:countries)
        attribute :region_id, Types::ForeignKey(:regions)

        primary_key :id

        associations do
          belongs_to :country
          belongs_to :region, foreign_key: :region_id

          has_many :regions, view: :children
        end
      end

      # Find a specific region.
      #
      # @param id [Integer]
      # @return [Country]
      def find(id)
        by_pk(id).one!
      end

      # Helps to build the aggregate/combine functions from +Graham::Repositories::CountriesRepository+.
      #
      # @example
      #   countries_repository.aggregate(:regions).one # => Graham::Entities::Country
      #
      # @param assoc [ROM::SQL::Associations::OneToMany] The association. We use this to build the query.
      # @param countries [Persistence::Relations::Countries] The countries we're querying for.
      # @return [Persistence::Relations::Regions] A relation with the correct query.
      def children(assoc, countries)
        assoc.target.where(region_id: nil, country_id: countries.pluck(:id))
      end

      struct_namespace ::Graham::Entities
      auto_struct true
    end
  end
end