title: Sequelize one to one relation
body: <p>I have two models, Video and Frame.</p>
  
  <pre><code>Frame.belongsTo(models.Video);
  Video.hasMany(models.Frame, { as: "Frames" });
  </code></pre>
  
  <p>I now need a way to specify first and last frame for a video, but can't get it to work.</p>
  
  <p>I tried this:</p>
  
  <pre><code>Video.hasOne(Frame, { as: "FirstFrame" });
  Video.hasOne(Frame, { as: "LastFrame" });
  </code></pre>
  
  <p>but that creates FirstFrameId and LastFrameId in the Frames table instead of the Videos table. I need to have video.get/setFirstFrame() and video.get/setLastFrame() functions available. How can I do this?</p>