title: using a variable in mongodb update
body: <p>Using Meteor, I'm trying to perform an update like the following: </p>
  
  <pre><code>Items.update(Session.get('selectedItem'), {'$set': {'directions.0.name': area.value}})
  </code></pre>
  
  <p>But I'm struggling with how to set the array index of directions dynamically, with something like this:</p>
  
  <pre><code>var index = //a value determined dynamically
  Items.update(Session.get('selectedItem'), {'$set': {'directions[index]name': area.value}})
  </code></pre>
  
  <p>This doesn't work because [index] is wrapped in a string. I also tried to form a custom string, like this: </p>
  
  <pre><code>var string = 'directions.'+itemIndex+'.name'
  Items.update(Session.get('selectedItem'), {'$set': {string: area.value}})
  </code></pre>
  
  <p>But that doesn't work. Any idea on how to do this?</p>