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Is it possible to define a CanCanCan ability by reference to another ability?

For example, I have models called Project and Project Question.

I want to allow a class of users to read projects and then if they can read the projects then they can create project questions.

I have defined the abilities for users to read Projects as:

can :read, Project, 
      {:active => true, 
       :closed => false,
       :sweep => { :disclosure => { :allusers => true }}
      }

Now I'd like to define an ability to create a project question. I'm wondering whether you can say something along the lines of:

if can :read, Project, can :create, ProjectQuestion

I have also tried:

can [:create, :read], ProjectQuestion do |pq3|
        if can :read Project 
        end

Is it possible to define one ability by reference to another one?

PS: this is not a duplicate of my other question about cancancan which is asking for help with syntax in expressing ability by reference to attributes in the db.

Mel
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  • possible duplicate of [Rails 4 - CanCanCan - syntax](http://stackoverflow.com/questions/32431123/rails-4-cancancan-syntax) – Roman Kiselenko Sep 07 '15 at 04:54
  • Hi - no not a duplicate of my other question. I have several questions about cancancan. the question you suggested is a duplicate is one i asked and is a different question – Mel Sep 07 '15 at 05:42

1 Answers1

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Assuming there's has_many/belongs_to type of assciation you can easily do it this way:

can [:create, :read], ProjectQuestion do |project_question|
  can? :read, project_question.project
end

Mind that you'll have to assign a project_id to the new project_question before checking the ability.

So in your controller/views you cannot do

can? :create, ProjectQuestion.new

as it will always return false. You will have to do:

can? :create, some_project.project_questions.new
ddgd
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