title: In which model does this belong?
body: <p>I often get confused as to which model to create functions. Let me try to explain my current situation with a simple made up example:</p>
  
  <p>I have a <code>Log</code> model that contains all activities on our app. I want to get the activity for a specific user. Should I create a <code>getActivity($userId)</code> function in the <code>User</code> model or the <code>Log</code> model?</p>