title: MongoDB Query Help - query on values of any key in a sub-object
body: <p>I want to perform a query on this collection to determine which documents have any keys in things that match a certain value.  Is this possible?</p>
  
  <p>I have a collection of documents like:</p>
  
  <pre><code>{
      "things": {
          "thing1": "red",
          "thing2": "blue",
          "thing3": "green"
      }
  }
  </code></pre>
  
  <p>EDIT: for conciseness  </p>