I have extended the user model to allow me to do .can? checks on the user.

class User < ApplicationRecord
  def ability
    @ability = Ability.new self
  end
  delegate :can?, :cannot?, :to => :ability
end

This allows me to do things like @some_user.can? :edit, Book and get a result. (The cancan view helper, but in the model.). This works great.

I'd like to be able to do a reverse of that though and get all users that can do an action.

Example: Give me all users that can :edit, Books. User.can? :edit, Book which returns an active record collection.

To get this to work I did this;

class User < ApplicationRecord
  def self.can? sym, obj, *args
    uids = []
    User.all.each do |user|
      uids << user.id if user.can? sym, obj, args
    end
    User.where id: uids
  end
end

While this works, it feels really icky as it's iterating through each user and I'm concerned about scale.. is there a faster way to do this??