many-to-many with rom repo

output.txt

I, [2015-11-11T18:21:57.978652 #52590]  INFO -- : (0.000162s) CREATE TABLE `users` (`id` integer NOT NULL PRIMARY KEY AUTOINCREMENT, `name` varchar(255))
I, [2015-11-11T18:21:57.978842 #52590]  INFO -- : (0.000069s) CREATE TABLE `groups` (`id` integer NOT NULL PRIMARY KEY AUTOINCREMENT, `name` varchar(255))
I, [2015-11-11T18:21:57.979020 #52590]  INFO -- : (0.000062s) CREATE TABLE `users_groups` (`user_id` integer REFERENCES `users`, `group_id` integer REFERENCES `groups`)
I, [2015-11-11T18:21:57.979194 #52590]  INFO -- : (0.000039s) INSERT INTO `users` (`id`, `name`) VALUES (1, 'Jane')
I, [2015-11-11T18:21:57.979321 #52590]  INFO -- : (0.000027s) INSERT INTO `groups` (`id`, `name`) VALUES (1, 'Admins')
I, [2015-11-11T18:21:57.979398 #52590]  INFO -- : (0.000025s) INSERT INTO `groups` (`id`, `name`) VALUES (2, 'Editors')
I, [2015-11-11T18:21:57.979486 #52590]  INFO -- : (0.000025s) INSERT INTO `users_groups` (`user_id`, `group_id`) VALUES (1, 1)
I, [2015-11-11T18:21:57.979558 #52590]  INFO -- : (0.000026s) INSERT INTO `users_groups` (`user_id`, `group_id`) VALUES (1, 2)
I, [2015-11-11T18:21:57.983559 #52590]  INFO -- : (0.000073s) SELECT NULL AS 'nil' FROM `users` LIMIT 1
I, [2015-11-11T18:21:57.983850 #52590]  INFO -- : (0.000118s) PRAGMA table_info('users')
I, [2015-11-11T18:21:57.984432 #52590]  INFO -- : (0.000043s) SELECT NULL AS 'nil' FROM `groups` LIMIT 1
I, [2015-11-11T18:21:57.984604 #52590]  INFO -- : (0.000057s) PRAGMA table_info('groups')
I, [2015-11-11T18:21:57.987130 #52590]  INFO -- : (0.000072s) SELECT * FROM `users`
I, [2015-11-11T18:21:57.987572 #52590]  INFO -- : (0.000081s) SELECT `groups`.`id`, `groups`.`name`, `users_groups`.`user_id` FROM `groups` INNER JOIN `users_groups` ON (`users_groups`.`group_id` = `groups`.`id`) WHERE (`user_id` IN (1))
[#<ROM::Struct[User] id=1 name="Jane" groups=[#<ROM::Struct[Group] id=1 user_id=1 name="Admins">, #<ROM::Struct[Group] id=2 user_id=1 name="Editors">]>]

rom_repo_many_to_many.rb

require 'rom'
require 'rom-sql'
require 'rom-repository'
require 'logger'

ROM.use(:auto_registration)
ROM.setup(:sql, 'sqlite::memory')

conn = ROM::SQL.gateway.connection
conn.loggers << Logger.new($stdout)

conn.create_table(:users) do
  primary_key(:id)
  String(:name)
end

conn.create_table(:groups) do
  primary_key(:id)
  String(:name)
end

conn.create_table(:users_groups) do
  foreign_key(:user_id, :users)
  foreign_key(:group_id, :groups)
end

conn[:users].insert(id: 1, name: 'Jane')
conn[:groups].insert(id: 1, name: 'Admins')
conn[:groups].insert(id: 2, name: 'Editors')
conn[:users_groups].insert(user_id: 1, group_id: 1)
conn[:users_groups].insert(user_id: 1, group_id: 2)

class Users < ROM::Relation[:sql]
end

class Groups < ROM::Relation[:sql]
  view(:for_users, [:id, :user_id, :name]) do |users|
    select(
      :groups__id, :groups__name, :users_groups__user_id
    ).inner_join(
      :users_groups, group_id: :groups__id
    ).where(
      user_id: users.map { |u| u[:id] }
    )
  end
end

class Repo < ROM::Repository::Base
  relations :users, :groups

  def users_with_groups
    users.combine_children(many: groups.for_users).to_a
  end
end

repo = Repo.new(ROM.finalize.env)

puts repo.users_with_groups.inspect

I've not been able to use the view method as you show it here, i.e., it's reported as undefined. I used latest the gemfiles from Rubygems. I also tried switching to github/master, but at the time there seemed to be an unresolvable dependency issue between the many gems coming from /master. I was also unable to get repositories to load as even my simplest attempt reports an error about base names. Thanks for the help and this example, probably will work fine for others.