title: Query key with value anywhere in object hierarchy in Mongo
body: <p>In Mongo how can I find all documents that have a given key and value, regardless of where that key appears in the document's key/value hierarchy?</p>
  
  <p>For example the input key <code>roID</code> and value <code>5</code> would match both:</p>
  
  <pre><code>{
    roID: '5'
  }
  </code></pre>
  
  <p>and</p>
  
  <pre><code>{
    other: {
      roID: '5'
    }
  }
  </code></pre>