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copied!<p>You want:</p> <pre><code>-(NSManagedObject *)existingObjectWithID:(NSManagedObjectID *)objectID error:(NSError **)error </code></pre> <p>Fetches the object from the store that has that ID, or nil if it doesn't exist.</p> <p>(Be aware: there are two methods on NSManagedObjectContext with similar-seeming names that tripped me up. To help keep them straight, here's what the other two do:</p> <pre><code>-(NSManagedObject *)objectWithID:(NSManagedObjectID *)objectID </code></pre> <p>...will create a fault object with the provided objectID, <strong>whether or not</strong> such an object actually exists in the store. If it doesn't exist, anything that fires the fault will fail unless you insert the object first with NSManagedObjectContext's <code>insertObject:</code>. The only use I've found for this is copying objects from store to store while preserving ObjectIDs.</p> <pre><code>-(NSManagedObject *)objectRegisteredForID:(NSManagedObjectID *)objectID </code></pre> <p>...will return the object that has that ID, <strong>if</strong> it has been fetched from the store by this managedObjectContext. If anyone knows what this method is useful for, please comment.)</p> <p>[eta.: Another important difference between the first method and the other two is that <code>existingObjectWithID:error:</code> never returns a fault; it always fetches the whole object for you. If you're trying to avoid that (e.g. working with an expensive-to-fetch object with a big blob property), you have to be clever with <code>objectWithID:</code> or <code>objectRegisteredForID:</code>, which don't fire faults; or use a properly configured fetch request.]</p>

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