Rolify: Can a User assign a specific Resource Role to another User?

Question

I'm trying to determine whether this flow is possible when using Rolify (with Devise and CanCanCan)... And, if so, how it would be implemented:

I have a class, Shop, which belongs to User. I'd like the user who created a respective Shop instance to be able to assign a Rolify role (:manager) to any user (N.B. any user who created an instance should be able to assign the role - not just a user who has the role :admin).

I know this can be achieved via the rails console through the add_role command (using, as an example, a Shop instance with id: 5):

user.add_role :manage, Shop.find(5)

But I'm not clear on whether or not this can be done programmatically by individual users - where a user can assign the role to another user. Specifically, by selecting the user from a searchable dropdown form and assigning the role on submit.

Though I don't yet have any code that's worth showing / helpful to show, I'm hoping to get direction here as to how best to approach this issue (e.g., should the action be defined in shops_controller.rb or in its own controller?). Also, would it be better to scrap using Rolify for this altogether and create a join table for shops_managers?

If it helps, here's the Ability.rb class:

    class Ability
      include CanCan::Ability

      def initialize(user)
        if user
          if user.has_role? :admin
            can :manage, :all
          else
            can [:edit, :update], Shop.with_role(:manager, user)
            can :manage, Shop, :user_id => user.id
            can :manage, User, id: user.id
            can :read, :all
          end
        end
      end

Thanks much!

Answer 1

You don't need join table to store shops_managers. You have a role model:
Role(id: integer, name: string, resource_id: integer, resource_type: string, created_at: datetime, updated_at: datetime)
It is perfectly fine to add the role in shops#create doing something like:

if @shop.save
  #some code
  @current_user.add_role :manager, @shop  
  #some more code
end

If you want to manage the roles it should be done in some other controller.. probably in admins namespace.