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copied!<p>It seems to me that your first instincts are right: you should use fetchrequests to update your existing store. The approach I used for an importer was the following: get a list of all the files that are eligible for importing and store it somewhere. I'm assuming here that getting that list is fast and lightweight (just a name and an url or unique id), but that really importing something will take a bit more time and effort and the user may quit the program or want to do something else before all the importing is done.</p> <p>Then, on a separate background thread (this is not as hard as it sounds thanks to NSRunLoop and NSTimer, google on "Core Data: Efficiently Importing Data"), get the first item of that list, get the object from Flickr or wherever and search for it in the Core Data database (carefully read Apple's Predicate Programming Guide on setting up efficient, cached NSFetchRequests). If the remote object already lives in Core Data, update the information as necessary, if not insert. When that is done, remove the item from the to-be-imported list and move on to the next one.</p> <p>As for the problem of objects that have been deleted in the remote store, there are two solutions: periodic syncing or lazy, on-demand syncing. Does importing a photo from Flickr mean importing the original thing and all its metadata (I don't know what the policy is regarding ownership etc) or do you just want to import a thumbnail and some info? If you store everything locally, you could just run a check every few days or weeks to see if everything in your local store is present remotely as well: if not, the user may decide to keep the photo anyway or delete it. If you only store thumbnails or previews, then you will need to connect to Flickr each time the user wants to see the full picture. If it has been deleted, you can then inform the user and delete it locally as well, or mark it as not being accessible any more. </p>

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