Question

I have a Rails app that pulls in music from Soundcloud. This data contains a title, which I save as mix.sc_title but it’s not always properly formatted. I have added an additional attribute on my Mix model which I call mix.override_title

For display on my site, I want to use the override title if available, and the sc_title in all other cases.

I have a Mix model method to do this for me

def display_title
    override_title.blank? sc_title : override_title
end

Mixes#index grabs @mixes = Mix.where(:active => true) and mixes/index.html.erb looks like this:

<ul>
<% @mixes.each do |mix| %>
    <li><%= link_to mix.display_title, mix %></li>
<% end %>
</ul>

As you can see, I’m not directly using any mix attributes, and so I take a huge hit when I go to the DB, and I don’t actually benefit from it.

Is there a leaner way to get just the information I need? (mix.display_title)

I have tried Mix.select("display_title").where(:active => true) but it fails because display_title is not a real DB column

Answer 1

You can do Mix.select("sc_title, override_title").where(:active => true) and it will work, since those are the actual fields that the method uses. I don’t really think getting the additional attributes gives you that much of a DB hit but sometimes selecting only what you need can be beneficial.

As you start chaining on more Arel commands, consider putting the select into a model method:

def select_active_titles
  select("sc_title, override_title").where(:active => true)
end

Edit: Your link_to helper also secretly calls mix.id to link to the right mix, so make sure it’s working and if not add id to the list of selected attributes.