title: Using primary keys with Ember Data
body: <p>I've been <strong>struggling</strong> for the past few days with <strong>primary keys</strong> and the last version of Ember Data.</p>
  
  <p>I first read how to do it on the <a href="https://github.com/emberjs/data/blob/master/BREAKING_CHANGES.md" rel="noreferrer">Breaking Changes file on GitHub</a>, but it's apparently outdated. I tried <a href="https://gist.github.com/anonymous/e44b07b142ca046e6b0a" rel="noreferrer">several</a> <a href="https://gist.github.com/anonymous/54f9fa49959c593036a8" rel="noreferrer">other</a> <a href="https://gist.github.com/anonymous/f7d31e0819cf1618abda" rel="noreferrer">ways</a> (with the help of Peter Wagenet on IRC), but none of them seem to work.</p>
  
  <p>I would like to make <code>slug</code> my primary key on my model, and also since I'm working with MongoDB, I would like to use <code>_id</code> instead of <code>id</code>.</p>
  
  <p>Has anyone figured out how to do this? My underlying problem is that model records get loaded twice when I do several <code>App.MyModel.find()</code> on the model.</p>