title: Find and remove all in mongo/mongoid
body: <p>Is there any way in mongoid to find and 'read' all documents in a collection while also removing them in one, atomic query?</p>
  
  <p>So far I was using:</p>
  
  <pre><code>Model.collection.find().to_json
  Model.delete_all
  </code></pre>
  
  <p>Which can be easily broken by adding more data to collection between those two instructions.</p>