title: Magento Upgrade 1.7 > 1.9 DB Issue
body: <p>I upgraded Magento 1.7 to 1.9 and after upgrade the add-to-cart doesn't work anymore. It is not connected to the form_key! Why i think it is a database issue:</p>
  
  <p>I used clean magento 1.9 with clean database and created one product, add-to-cart works fine. I connected this magento with the database i upgraded and add-to-cart didn't work.</p>
  
  <p>So clean Magento with "old" database doesn't work on add-to-cart.
  Has anyone an idea how to solve this? I don't really want to use a clean database and move data to this, because it is ~500k products and a lot of customers and orders.</p>
  
  <p><strong>Update:</strong></p>
  
  <p>I hooked into controller_action_postdispatch where the full action name is checkout_cart_add and checked what is in quote. There is one item in quote. I also hooked into controller_action_predispatch_checkout_cart_index and checked the quote, and the quote is empty. So somewhere inbetween the issue occures. The events inbetween are only model_saves or some resource_ events.</p>
  
  <p><strong>Update 1:</strong></p>
  
  <p>I logged all the executed SQL queries on this add-to-cart and checked if the quote is actually saved in database. The entry is correct in the sales_flat_quote. So my next idea is that somehow the connection of session and quote is missing, because i figured out that on cart_index the quote object is not set. I still think it is connected to DB because if i switch to some "originally installed" 1.9 db it works fine.</p>