hack around adding invalid objects to a has_many association

flow.rb

u = User.new
u.valid? == false
u.save(validate: false)

params = { dont_validate_user_ids: true, user_ids: [1] }
UserGroup.create(params)

User.first
=> #<User id: 1, name: nil, user_group_id: 1, created_at: "2015-04-15 12:37:58", updated_at: "2015-04-15 12:37:58">

user.rb

class UserGroup < AR::Base
  attr_accessor :dont_validate_user_ids
  
  has_many :users
  
  def user_ids=(user_ids)
    if dont_validate_user_ids
      User.where(id: user_ids).update_all(user_group_id: id)
    else
      super
    end
  end
end