gistfile1.rb

require 'rubygems'
require 'bundler/setup'
require 'rom'
require 'rom-sql'

ROM.setup(:sql, 'postgres://localhost/datsu_development')

class Players < ROM::Relation[:sql]
  register_as :players
  dataset :players

  def with_throws
    inner_join(:throws, player_id: :id)
  end
end

class Matches < ROM::Relation[:sql]
  register_as :matches
  dataset :matches
end

class Throws < ROM::Relation[:sql]
  register_as :throws
  dataset :throws

  def for_users(users)
    where(player_id: users.map { |user| user[:id] })
  end
end

ROM.finalize

rom = ROM.env

puts rom.relation(:players).to_a
puts '---'

puts rom.relation(:players).combine(rom.relation(:throws).for_users).to_a
puts '---'

puts rom.relation(:players).with_throws.to_a
puts '---'