custom validation markup in Rails(3)

I'm trying to accomplish the following mark-up开发者_开发技巧 for all my form elements

<div class="input-container">
  <label>Topic Title</label>
  <div class="input-holder">
    <input type="text" />
  </div>
</div>

<div class="textarea-container">
  <label>Post</label>
  <div class="textarea-holder">
    <textarea></textarea>
  </div>
</div>

invalid fields mark-up:

<div class="input-container alert">
  <label>Topic Title</label>
  <div class="input-holder">
    <input type="text" />
  </div>
</div>
<div class="textarea-container alert">
  <label>Post</label>
  <div class="textarea-holder">
    <textarea></textarea>
  </div>
</div>

here's my current haml markup:

.input-container
  = f.label :title, 'Topic Title'
  .input-holder
    = f.text_field :title
.textarea-container
  = f.label :body, 'Post'
  .textarea-holder
    = f.text_area(:body, :size => "60x10")

Now what would I need to do if I want the container divs to have the alert class when a field in my form is invalid?

I want to do the same thing but unfortunately haven't figured out a clean way to handle it.

You can override ActionView::Base.field_error_proc, but that doesn't help with the enclosing elements.

It can be done manually by checking errors on each field ('post.errors['body'].nil?') and outputting your alert class conditionally.

The next step could be extracting the logic into a view helper, and perhaps some further abstraction after that.

But it would still be nice to do this in a more automated, Rails-y fashion.

It might be best to use either the formtastic or simple_form gems which out of the box support highlighting an individual invalid field.

I'm almost certain they do this by changing the CSS class on the field or its container, which you could also hook into in your stylesheets.