title: How to see if a record with doesn't already exist
body: <p>I have a <code>Friendship</code> model which allows users to become friends with one another. The records for these <code>Frienships</code> has a <code>requesting_user_id</code> and an <code>accepting_user_id</code>. I want to build a method that checks to see that a record with the same accepting_user and requesting_user pair doesn't already exist. In short, that a one user has already befriended another user.</p>
  
  <p>I started this in my <code>User</code> model:</p>
  
  <pre><code>def can_befriend?(accepting_user)
    @accepting_user = Friendship.find_by_accepting_user_id(accepting_user)
    @requesting_user = current_user
  end
  </code></pre>
  
  <p>But I'm not sure how to check that the pair doesn't already exist. Any help?</p>