Having a unique selector for an element is useful to later select it from JavaScript or to update a fragment with an Unpoly Show archive.org snapshot .
Haml lets you use square brackets ([]) to generate a unique class name and ID from a given Ruby object. Haml will infer a class attribute from the given object's Ruby class. It will also infer an id attribute from the given object's Ruby class and #id method.
This is especially useful with ActiveRecord instances, which have a persisted #id and will hence generate the same selector over multiple renderings of the same view.
Example
- @users.each do |user|
.row[user]
= user.name
This compiles to:
<div class='user row' id='user_37'>Alice</div>
<div class='user row' id='user_38'>Bob</div>
Since the record's #id is part of the generated selector, it will be the same over multiple renderings of the same view.
Controlling the generated string
By default Haml will downcase and underscore the class name. So ForumPost will become forum_post.
You can control the generated string by overriding the #haml_object_ref method in the referenced object:
class ForumPost < ActiveRecord::Base
def haml_object_ref
'forum-comment'
end
end
