Rails cancan authorizing nested resources

Question

I have Projects resource which is nested in Users resource.

My Cancan Ability class is:

class Ability
  include CanCan::Ability
  def initialize(user)
    #everyone
    can :read, Project

    if user.blank? 
      # guest user
      ...
    else
      #every signed in user

      case user.role
        when User::ROLES[:admin] 
          #only admin role user
          can :manage, :all

        when User::ROLES[:member] 
          #only member role user
          can :update, User, :id => user.id
          can [:create, :update, :destroy], Project, :user_id => user.id
        else

      end
    end
  end
end

And Projects controller:

class ProjectsController < ApplicationController
  load_and_authorize_resource :user
  load_and_authorize_resource :projects, :through => :user, :shallow => true
  ...
end

I have few questions:

Is it possible to deny :read User and allow to :read Project, so that everyone could access /users/10/projects, but not /users/10 or /users?

How can I deny user accessing :new action with other user_id? For example, if I add

#everyone
can :read, User
can :read, Project

this code allows user with id 42 to access /user/41/projects/new.

Answer 1

Solved it by doing:

class Ability
  include CanCan::Ability

  def initialize(user)
    #everyone
    can :read, Project

    can :read, User # required to access nested resources
    cannot :index, User
    cannot :show, User

    if user.blank? 
      # guest user
      ...
    else
      #every signed in user

      case user.role
        when User::ROLES[:admin] 
          #only admin role user
          can :manage, :all

        when User::ROLES[:member] 
          #only member role user
          can :update, User, :id => user.id
          can :manage, Project, :user => { :id => user.id }
        else

      end
    end
  end
end