RSpec and CanCan Authorization for Intentional Economics

gistfile1.rb

    can :create, Exchange do |exchange|
      unless exchange.group
        # the presence of group is validated when creating an exchange
        # group will be nil for the new method, so allow it
        true
      else
        membership = Membership.mem(person,exchange.group)
        unless membership
          false
        else
          account = person.account(exchange.group)
          account && (account.authorized? exchange.amount)
        end
      end
    end