title: Quick way to retrieve doc from other doc's ref in Mongoose (Node.js)
body: <p>I have a model <code>Product</code> with a ref field <code>Grocer</code>. At some point I have the <code>Product</code> doc but with the <code>Grocer</code> field not populated, just the ObjectId. Is there a quick way to populate a doc using mongoose? or I have to extend it somehow?, so from: </p>
  
  <pre><code>// product 'product1'
  {
    _id: 'ksjdflasdf78aslwk3jk8df9',
    name: 'Product 1',
    grocer: 'jasf97342jlihwe79834hkjhdkf'
  }
  </code></pre>
  
  <p>I could do something like:</p>
  
  <pre><code>doc.populate('grocer');
  </code></pre>
  
  <p>Now doc is:</p>
  
  <pre><code>// product 'product1'
  {
    _id: 'ksjdflasdf78aslwk3jk8df9',
    name: 'Product 1',
    grocer: {
      _id: 'jasf97342jlihwe79834hkjhdkf',
      name: 'Johan'
    }
  }
  </code></pre>