title: Querying key-value map in mongo
body: <p>I have documents stored in mongo database following this schema:</p>
  
  <pre><code>{
     map:{
           key1:value,
           banana:value2 
           ....
          }
  
  }
  </code></pre>
  
  <p>How can I query objects based on keys in this map ?</p>
  
  <p>e.g I want to get all the documents which map contains key that equals <code>banana</code>.</p>