title: MongoDB finding nested elements
body: <p>I am using the MongoDB shell and I need to find some nested elements.
  My structure looks like this:</p>
  
  <pre><code> car : { "$ref" : "cars" , "$id" : { "$oid" : "4e8478ace4b0dea06288ad63"}}
  </code></pre>
  
  <p>I need to get to the <code>oid = 4e8478ace4b0dea06288ad63</code></p>
  
  <p>thanks in advance </p>
  
  <p>Here is the structure :</p>
  
  <pre><code>{ "_id" : { "$oid" : "4e7c6b68e4b0dea06288ad22"} , 
    "driver" : "Test Driver" , 
    "category" : "BUSINESS" , 
    "distanceM" : 216.857 , 
    "mileageKmStart" : 121813.943 , 
    "mileageKmEnd" : 122030.8 , 
    "timestampStart" : { "$date" : "2012-01-12T11:20:08Z"} , 
    "timestampEnd" : { "$date" : "2012-01-12T11:21:11Z"} , 
    "car" : { 
        "$ref" : "cars" , 
        "$id" : { "$oid" : "4e8478ace4b0dea06288ad63"}
     }
  }
  </code></pre>