title: ActiveRecord: size vs count
body: <p>In Rails, you can find the number of records using both <code>Model.size</code> and <code>Model.count</code>. If you're dealing with more complex queries is there any advantage to using one method over the other? How are they different?</p>
  
  <p>For instance, I have users with photos. If I want to show a table of users and how many photos they have, will running many instances of <code>user.photos.size</code> be faster or slower than <code>user.photos.count</code>?</p>
  
  <p>Thanks!</p>