核心数据问题——检查项目是否存在

I am working on a code example from NSScreenCast that deals with importing to a Core Data application. (https://github.com/subdigital/nsscreencast/tree/master/012-core-data-importing-data/BeerBrowser). I have the example working for the most part. I am able to push the refresh button, it parses the json and imports it in to the database. However, every time I press the refresh button it re-adds the same data. I have traced it down to the following code.I am working on a code example from NSScreenCas