f.collection_select explained

f.collection_select

f.collection_select :x, query, :y, :z

:x = the value of the select id and name
query = the query sent to the database to return values
:y = the values in the options
:z = what you want displayed in the drop down menu


So if you have a Model that has an alias and an ID you would render it like this


:x = alias
query = Model.group(:itemtogroupby)
:y = id
:z = displayed_attribute

f.collection_select :alias, Location.group(:itemtogroupby), :value_id, :displayed_attribute

And it will render out a list that is grouped by your itemtogroupby like this

<select id="model_alias" name="model[alias]">
  <option value="value_id">diplayed_attribute</option>
</select>

The value_id and displayed_attribute will be evaluated for the value of that attribute of your query.