选择带有多个预选值的标签-在数据库中手动插入值

我需要在select_tag中预先选择多个值。但是我在表空缺中“手动”添加了空缺，如下所示：

我的控制器：

def create
  @hr_curriculum_generic = HrCurriculumGeneric.new(params[:hr_curriculum_generic])

  if params[:vacancy_ids].present?
    @vacancies_ids = params[:vacancy_ids]

-我的表格：

  @vacancies_ids.each do |vacancy_id|
    # Armazena os id do curriculum, vaga e do cargo na tabela CandidatosxVagas
    @candidates_vacancies = CandidatesVacancy.new 
    <% @vacancies = Vacancy.all %>
    <%= select_tag "vacancy_ids[]", options_from_collection_for_select(Vacancy.all, "id", "title"), :multiple => true, :id => "vacancy_ids", :class => "form-control" %>

.....

它有效，但是当我单击编辑btn时，未预先选择字段。