title: Is it possible to ask for only certain columns from an ActiveRecord association?
body: <p>consider</p>
  
  <pre><code>def Foo
    has_one :user
  end
  </code></pre>
  
  <p>let's say i only want a <code>Foo</code>'s <code>User</code>'s name, and not any of the other columns. so i want</p>
  
  <pre><code>SELECT name FROM "users" WHERE "prices"."id" = 123
  </code></pre>
  
  <p>but doing <code>foo.user.name</code> will give me</p>
  
  <pre><code>SELECT * FROM "users" WHERE "prices"."id" = 123
  </code></pre>
  
  <p>is there any slick way to use the association to get only one column? if not, then i have to do:</p>
  
  <pre><code>User.where(id: foo.user_id).pluck(:name).first
  </code></pre>