Helper for Cancancan gem.

Increase accessible_by query performance via ability merging.

If your app have more than one ability declaration for one resource

can :index, User, id: [1, 2, 3]
can :index, User, id: [4, 5, 6]

User.accessible_by(ability, :index) generates sql query like that:

SELECT users.* FROM users WHERE (users.id IN (4, 5, 6)) OR (users.id IN (1, 2, 3))

In case of big data that fact causes significant performance issue.

Cancando helps to avoid that situation by merging conditions:

can :index, User, id: [1, 2, 3, 4, 5, 6]

Add this line to your application's Gemfile:

gem 'cancando'

And then execute:

$ bundle

Or install it yourself as:

$ gem install cancando

Important. You have to install Cancancan gem first.

1. Add include Cancando
2. User can_do and cannot_do instead of can and cannot from cancancan
3. Call apply for merge and save abilities

Simple example:

class Permission
  include Cancando
  
  def grant_permission
    can_do :index, User, company_id: available_company_ids
    can_do :update, Company, id: current_user.company_id
    apply
  end
end

Bug reports and pull requests are welcome on GitHub at https://github.com/viktormarkov/cancando. This project is intended to be a safe, welcoming space for collaboration.

The gem is available as open source under the terms of the MIT License.