Nested associations with rom-rb

problem.rb

# Hi, this is the setup of my problem.

# The thing is that I'm working in a legacy database where primary keys are not autoincrement ids,
# They're strings and are named <<entity>>_id.
# Also some foreign keys are named diferrently like the one for zones in journeys relation, that is named
# start_zone_id
#
# The queries that I pretend to implement are explained in comments in the repository class.

  class Interval < ROM::Relation[sql]
    schema(:interval) do
      attribute :interval_id, Types::String.meta(prmary_key: true)
      attribute :journey_id, Types::ForeignKey(:journeys, Types::String)
      attribute :state, Types::String
      attribute :created_at, Types::DateTime

      associations do
        belongs_to :journey
      end
    end
  end

  class Journey < ROM::Relation[sql]
    schema(:interval) do
      attribute :journey_id, Types::String.meta(prmary_key: true)
      attribute :description, Types::String
      attribute :start_zone_id, Types::ForeignKey(:zones, Types::String)

      associations do
        belongs_to :zone
        has_many :intervals
      end
    end
  end

  class Zone < ROM::Relation[sql]
    schema(:interval) do
      attribute :zone_id, Types::String.meta(prmary_key: true)
      attribute :name, Types::String

      associations do
        has_many :journeys
      end
    end
  end

  class IntervalRepo < ROM::Repository[:intervals]

    def first_query(initial_date, final_date)
      # I pretend to have a query that retrieves all the intervals created between initial and final dates.
      # And retrieve at the same time the journeys and the zones associated, nested in the same resulset.
    end

     def second_query(initial_date, final_date)
      # The same as the first query, with the difference that I would like to retrieve the associated journeys and zones
      # only for intervals in some state.
      # All the intervals, but only with associated data the ones in some stae
    end

  end