title: Using acts-as-taggable-on in a collection_select form
body: <p>I am having a model Movie that has tags, using the gem acts_as_taggable_on.</p>
  <p>I can do this in the form:
  &lt;%= form.text_input :tag_list %&gt;
  and it works - it shows the tags associated with the movie, and I can add tags, separated by commas, all fine.</p>
  <p>I am now trying to use a collection_select helper, and I had two ideas: using &quot;:tag_ids&quot; as first parameter, which makes DISPLAYING the tags assigned to movies properly (as selected), but not updated, or using &quot;:tag_list&quot; which makes tag updates work but not displaying...</p>
  <pre><code>&lt;%= form.collection_select(:tag_list, @all_tags, :id, :name, { }, { class: 'font-size-m', id: 'tag-select', multiple: true }) %&gt;
  </code></pre>
  <p>(I define @all_tags in the controller as follows):</p>
  <pre><code>@all_tags = ActsAsTaggableOn::Tag.all
  </code></pre>
  <p>Not sure how to use a collection_select with these tags... any help appreciated!</p>