title: Turn off whole document update in meteor
body: <p>I frequently write a meteor.update function like this:</p>
  
  <pre><code>Books.update(bookId, {"author": "George"});
  </code></pre>
  
  <p>Notice the mistake in my code: no <code>$set</code> operator - meteor will interpret the object argument as a whole document update, and replaces the entire book record with what I intended to be a modifier.</p>
  
  <p><strong>Is there a way to turn off whole document updates in the server side?</strong></p>
  
  <p>Note: one reason I have to write this modifier on the server side is that I can't write child array modifiers on the client side:</p>
  
  <pre><code>Books.udpate({
    _id: bookId,
    "readers._id": "123"
  }, {
    $set: {
      "readers.$.name": "Ralph Reader"
    }
  })
  </code></pre>