Rails 4：actions_as_taggable_on的text_field没有用逗号分隔标签

I am trying to get the text_field in my form partial to comma-separate acts_as_taggable_on tags. Right now, when I reload the page, the commas disappear so if a field has two or more tags, they become one big tag instead. For instance, I get "Tag1 Tag2 Tag3" instead of "Tag1, Tag2, Tag3". I am using acts-as-taggable-on 3.4.2.I am trying to get the text_field in my form pa