ROM commands chaining with mapper

gistfile1.rb

require "rom"
ROM.setup :memory

class Users < ROM::Relation[:memory]
  register_as :users
end

class Tasks < ROM::Relation[:memory]
  register_as :tasks
end

class CreateUser < ROM::Commands::Create[:memory]
  relation :users
  register_as :create
  result :one

  def execute(user)
    super user
  end
end

class CreateTask < ROM::Commands::Create[:memory]
  relation :tasks
  register_as :create
  result :one

  def execute(task, user)
    super task.merge(user)
  end
end

class UserToTask < ROM::Mapper
  relation :users
  register_as :task
  reject_keys true
  attribute :user_id, from: :id
end

rom = ROM.finalize.env

command =   rom.command(:users).as(:task).create.with(id: 1, name: "Jane")
command >>= rom.command(:tasks).create.with(title: "Sleep well")
command.call
# => { user_id: 1, title: "Sleep well" }