:manage Cancan

Ability.rb

permissions = Permission.find_all_by_group_id(<id_do_grupo_do_usuario>)

cannot :manage, :all

actions = ""
models = ""

# dps vai verificando as permissoes do usuario, e permitindo. tipo:
permissions.each do |permission|
  actions = permission.action
  models  = permission.model.singularize.constantize
  can actions, models
end