Collection select is kind of a badass. Imagine you have a collection of items. You want to choose one of these items from a form and send it back to the controller. The docs aren’t super helpful, so here ya go:
<% form_for @something do |f| %>
<%= f.label 'Some attribute to associate with Something'%>
<%= f.collection_select(
:attribute_id,
Attribute.all,
:id,
:name,
{include_blank: true},
{class: "form-control"}
) %>
<% end %>
Wow, that’s a lot of arguments! Collection Select takes four to six arguments. The last two are optional, but if you want to add the last, you need to add the second-to-last. Let’s figure out what these things are!
The first argument will be the key in the param headed back to the controller. In the case above, the param will be param[:something][:attribute_id].
The second argument is the collection of objects the user can select from in the drop-down. This can be passed in from the controller as an instance variable, or an ActiveRecord query.
The third argument is the value in the param that will be send back to the controller, and the fourth is the value that the user will see in the drop-down. Both the third and fourth arguments must be methods that you can call on the objects in the collection.
The fifth and sixth arguments are options, the fifth being options for the items in the drop-down, like whether there should be a blank spot or if an empty selection should say something like “Please select one of the following attributes”. The sixth option are the html options… this is where you can put classes on the select-box.
For some collection-selection madness, check out my super-alpha Herbal Notebook project!
Go forth and select from some collections!