test.rb

#!/usr/bin/env ruby
require "rom-sql"
require "rom-repository"
require "byebug"

module Persistence
  module Relations
    class Configurations < ROM::Relation[:sql]
      gateway :alternate

      schema(:bns_configurations, infer: true, as: :configurations) do
        associations do
          has_many :parameters
        end
      end
    end

    class Parameters < ROM::Relation[:sql]
      gateway :alternate

      schema(:bns_parameters, infer: true, as: :parameters) do
        associations do
          belongs_to :configuration
        end
      end
    end
  end
end

module Repositories
  class Configurations < ROM::Repository[:configurations]
    commands :create, update: :by_pk
    relations :parameters

    def by_id(id)
      aggregate(:parameters).by_pk(id).one!
    end
  end
end

config = ROM::Configuration.new(default: [:sql, "sqlite::memory"],
                                alternate: [:sql, "postgres://localhost:5432/rom_sql"])

config.gateways[:alternate].tap do |gateway|

  migration1 = gateway.migration do
    change do
      create_table :bns_configurations do
        primary_key :id
        column :description, String, null: false
      end
    end
  end

  migration2 = gateway.migration do
    change do
      create_table :bns_parameters do
        primary_key :id
        column :configuration_id, Integer, null: false
        column :description, String, null: false
        column :value, Integer, null: false
        index :configuration_id
      end
    end
  end

  migration1.apply gateway.connection, :up
  migration2.apply gateway.connection, :up
end

config.register_relation Persistence::Relations::Configurations
config.register_relation Persistence::Relations::Parameters

container = ROM.container(config)

puts container.relations[:configurations].class.dataset # => bns_configurations
puts container.relations[:parameters].class.dataset # => bns_parameters

repo = Repositories::Configurations.new(container)
repo.create(description: 'test')
data = repo.by_id(1)