title: Sequelize's dynamic set/get methods for assoctiations
body: <p>The only reference in Sequelize's documentation that I could find about this  is at <a href="http://docs.sequelizejs.com/en/latest/docs/associations/" rel="nofollow">Relations / Associations</a>.</p>
  
  <p>Apparently, if you have something like:</p>
  
  <pre><code>Person.hasOne(Person, {as: 'Father', foreignKey: 'DadId'})
  </code></pre>
  
  <p>then you can do something like:</p>
  
  <pre><code>Person.setFather();
  Person.getFather();
  </code></pre>
  
  <p>As far as I understand, these set and get methods are created dynamically for associations.</p>
  
  <p>However, I have tried something similar and it does not work:</p>
  
  <pre><code>Person.hasOne(Father, { foreignKey: 'father_id' });
  
  var aPerson = Person.build({
      name: 'Mike'
  });
  
  aPerson.setFather({ id: 1 });
  </code></pre>
  
  <p>I realized that the <code>{ id: 1 }</code> bit may not be correct, but the problem is that I get a message saying that the setFather function is <code>undefined</code>.</p>
  
  <p>Basically, my question is: how can I attach associations to an already-created instance of some model in Sequelize?</p>