title: Extjs 5 hasMany vs field.reference
body: <p>I'm struggling to understand the different types of data bindings in ExtJS and I couldn't figure this out:</p>
  
  <p>What is the difference between "hasMany" and "field.reference" when defining associations on two models?</p>
  
  <p>When should I use "hasMany" and when is "reference" better?</p>
  
  <p>For example, if I want to define multiple email addresses to one user, what is the best practice so I can use the email model elsewhere too?</p>
  
  <p>I'm aware that I have 3 questions, but these seem to belong together.</p>
  
  <p>Thanks!</p>