title: How to add key-value pair to object in MongoDB
body: <p>If I have a document with the following basic structure:</p>
  
  <pre><code>{
    ...
    Monday: { a:1, b:2 },
    Tuesday: { c:3, d:4 }
    ...
  }
  </code></pre>
  
  <p>Am I able to 'push' an additional key:value pair to Monday's value? Result would be:</p>
  
  <pre><code>{
    Monday: { a:1, b:2, z:8 },
    Tuesday: { c:3, d:4 }
    ...
  }
  </code></pre>
  
  <p>The <code>$push</code> operator seems to only work for arrays. </p>