title: How to update DjangoItem in Scrapy
body: <p>I've been working with Scrapy but run into a bit of a problem.</p>
  
  <p><code>DjangoItem</code> has a <code>save</code> method to persist items using the Django ORM. This is great, except that if I run a scraper multiple times, new items will be created in the database even though I may just want to update a previous value.</p>
  
  <p>After looking at the documentation and source code, I don't see any means to update existing items.</p>
  
  <p>I know that I could call out to the ORM to see if an item exists and update it, but it would mean calling out to the database for every single object and then again to save the item.</p>
  
  <p>How can I update items if they already exist?</p>