decompose_container.rb

require 'rom'
require 'rom-repository'

rom = ROM.container(:sql, 'sqlite::memory') do |c|
  c.default.create_table(:users) do
    primary_key :id
    column :name, String
  end

  c.default.create_table(:tasks) do
    primary_key :id
    foreign_key :user_id, :users
    column :title, String
  end
end

my_relations = ROM::RelationRegistry.new do |r, h|
  h[:tasks] = rom.relations[:tasks]
end

my_container = ROM::Container.new(rom.gateways, my_relations, {}, {})

puts my_container.inspect

class MyRepo < ROM::Repository
  relations :tasks
end

repo = MyRepo.new(my_container)

puts repo.relations.inspect