title: Mongoose: deep population (populate a populated field)
body: <p>I have <code>Category</code> model:</p>
  
  <pre><code>Category:
      ...
      articles: [{type:ObjectId, ref:'Article'}]
  </code></pre>
  
  <p>Article model contains ref to <code>Account model</code>. </p>
  
  <pre><code>Article:
      ...
      account: {type:ObjectId, ref:'Account'}
  </code></pre>
  
  <p>So, with populated <code>articles</code> Category model will be:</p>
  
  <pre><code>{ //category
      articles: //this field is populated
       [ { account: 52386c14fbb3e9ef28000001, // I want this field to be populated
           date: Fri Sep 20 2013 00:00:00 GMT+0400 (MSK),
           title: 'Article 1' } ],
      title: 'Category 1' }
  </code></pre>
  
  <p>The questions is: how to populate subfield (account) of a populated field ([articles])? Here is how I do it now:</p>
  
  <pre><code>globals.models.Category
      .find
          issue : req.params.id
          null
          sort:
              order: 1
      .populate("articles") # this populates only article field, article.account is not populated
      .exec (err, categories) -&gt;
          console.log categories
  </code></pre>
  
  <p>I know it was discussed here: <a href="https://stackoverflow.com/questions/8543940/mongoose-populate-a-populated-field">Mongoose: Populate a populated field</a> but no real solution was found</p>