title: MongoDB Update (Insert a List of Item to an Array)
body: <p>I want to add several items to arrays of several rows in Mongo.  How can I do this?</p>
  
  <p>I want to start with this:</p>
  
  <pre><code>{'x': 'h', arr: [1,2,3] }
  {'x': 'h', arr: [1,3] }
  </code></pre>
  
  <p>and add the array [6,8], where the x is equal to 'h':</p>
  
  <pre><code>{'x': 'h', arr: [1,2,3,6,8] }
  {'x': 'h', arr: [1,6,8] }
  </code></pre>