title: Can't find documents searching by ObjectId using Mongoose
body: <pre><code>  Campaign.find {client_id:req.param('client_id')}, (error, campaigns) -&gt;
      if error
        response =
          error: error.message
      else
        for campaign in campaigns
          query =
            campaign_id: campaign._id
          console.log query
          CampaignResponse.find query, (err, campaignResponsesCount) -&gt;
            console.log campaignResponsesCount
  
        response = campaigns
  
      res.json response
  </code></pre>
  
  <p>For some reason, this returns <strong>no</strong> results. However, there are items in <code>CampaignResponse</code> with that specific <code>campaign._id</code>. I'm pretty sure this is an issue with types and casting, but I can't figure out what to do.</p>
  
  <p>Any help?</p>