ROM Mapper issue

mapper.rb

require 'bundler'
require 'dry-types'
Bundler.require

module Types
  include Dry::Types.module
end

rom = ROM.container(:sql, 'sqlite::memory') do |conf|
  conf.gateways[:default].use_logger(Logger.new($stdout))

  conf.default.create_table(:users) do
    primary_key :id
    column :login, String, null: false
  end

  conf.default.create_table(:employees) do
    primary_key :id
    column :name, String, null: false
  end

  conf.default.create_table(:customers) do
    primary_key :id
    column :address, String, null: false
  end

  conf.default.create_table(:employees_users) do
    foreign_key :verifable_id, :employees
    foreign_key :user_id, :users
  end

  conf.default.create_table(:customers_users) do
    foreign_key :verifable_id, :customers
    foreign_key :user_id, :users
  end

  conf.relation(:users) do
    schema(:users, infer: true) do
      associations do
        has_one :employees_user
        has_one :customers_user
        has_one :employee, through: :employees_users
        has_one :customer, through: :customers_users
      end
    end
  end

  conf.relation(:employees) do
    schema(:employees, infer: true) do
      associations do
        has_one :employees_user

        # belongs_to :c
      end
    end
  end

  conf.relation(:customers) do
    schema(:customers, infer: true) do
      associations do
        has_one :customers_user

        # belongs_to :a
        # belongs_to :b
      end
    end
  end

  conf.relation(:customers_users) do
    schema(:customers_users, infer: true) do
      associations do
        belongs_to :user
        belongs_to :customer
      end
    end
  end

  conf.relation(:employees_users) do
    schema(:employees_users, infer: true) do
      associations do
        belongs_to :user
        belongs_to :employee
      end
    end
  end
end

module E
  class User < ROM::Struct
    attribute :login, Types::String
  end
end

class UserRepo < ROM::Repository[:users]
  struct_namespace E

  def by_id(id)
    users
      .combine(:customer)
      .combine(:employee)
      .by_pk(id)
      .one
  end
end

employee = rom.relations[:employees].changeset(:create, name: 'Jane').commit

user = rom.relations[:users]
  .changeset(:create, login: 'jane@doe.org')
  .commit

rom.relations[:employees_users]
  .changeset(:create, user_id: user[:id], verifable_id: employee[:id]).commit

repo = UserRepo.new(rom)

user = repo.by_id(1)

p user
#<E::User login="jane@doe.org" id=1 login="jane@doe.org" customer=nil employee=#<E::Employee id=1 name="Jane" user_id=1>>