Rolify: Remove all roles for a resource and enforce only one role per resource (singleton pattern)

user.rb

class User < ApplicationRecord
	rolify :strict => true, :before_add => :before_add_role

  #Helper method to remove any existing role this user has for a resource
	def remove_all_roles resource
    # README: This syntax relies on changes on the following PR
    # https://github.com/RolifyCommunity/rolify/pull/427
    # Or include the source of this directly:
    # gem 'rolify', :git => "git://github.com/Genkilabs/rolify.git"
		remove_role nil, resource
	end

protected

	#ensure that we only have a single role per resource
	def before_add_role(role)
		if role.resource
			Rails.logger.debug "User::before_add_role: Adding the role of #{role.name} for #{role.resource_type} #{role.resource_id} to user #{id}"
			#remove any pre-existing role this user has to the resource
			remove_all_roles role.resource
		end
	end
end

This is my solution to the problems of wanting an elegant way to remove any number of unknown roles from a known resource.
You can call it directly with the syntax current_user.remove_role nil, some_resource

It relies on the following change to your ActiveRecord or Mongoid adapter:
Genkilabs/rolify@eb96834