ruby on rails乘以设置选择功能

Question

我目前在表单中有以下选择框：

%h1 Create New Movie

= form_tag movies_path do

  = label :movie, :title, 'Title'
  = text_field :movie, 'title'
  = label :movie,:description,'Description'
  = text_field :movie,'description'


  = label :movie, :rating, 'Rating'
  = select :movie, :rating, ['G','PG','PG-13','R','NC-17','SSS'],:multiple => true

  = label :movie, :release_date, 'Released On'
  = date_select :movie, :release_date

  = submit_tag 'Save Changes'

我想为此选择框添加多个选项，然后添加multiply =＆gt;选择功能后为true，但仍然只能选择一个等级。