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    <p>Okay, let's look at the symptoms here. You are making changes to objects within a context, but when you restart the app, some but not all of these changes are there.</p> <p>This can only mean that these changes are not being written to the persistent store. Since you are seeing some of the changes, you are calling the <code>save:</code> method, but Core Data is not recognising all the objects as needing to be saved.</p> <p>This leads us to how you are performing the changes to said objects. Are you making the changes in a KVO-compliant manner? Core Data relies on KVO to know what changes have occurred, and therefore what changes need persisting. If you change the objects in a non-KVO fashion, they will appear to be changed when you examine them, but Core Data will not know that these changes exist, and will therefore not know that it must persist them.</p> <p>I would amend your code as follows, providing the <code>Service</code> object has the inverse relationship back to the <code>User</code> (and that relationship is called <code>user</code>, and part of a 1-M):</p> <pre><code>[servicesToAdd setValue:self.user forKey:@"user"]; NSError *error = nil; if (![[service managedObjectContext] save:&amp;error]) { NSLog(@"Saving failed"); NSLog(@"Error: %@", [error localizedDescription]); } </code></pre> <p>This relies on the fact that Core Data will take care of both ends of the relationship for you, where an inverse relationship is set up. Of course, if it's a many-to-many relationship, then the code is slightly different, but we still use the KVO-compliant methods to make the changes.</p> <pre><code>[servicesToAdd setValue:self.user forKey:@"user"]; for (Service *service in servicesToAdd) { [user addServicesObject:service]; } NSError *error = nil; if (![[service managedObjectContext] save:&amp;error]) { NSLog(@"Saving failed"); NSLog(@"Error: %@", [error localizedDescription]); } </code></pre>
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    1. POSome CoreData relationships are lost after closing app
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    1. USpaulbailey
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    1. COIt's a M-M relationship. I recognize now that I can't use the dot accessor directly to add the objects and I was also understanding that CD takes care of the reverse relationships. Also, I've tried to use the `addServicesObject` instead of the dot accessor with similar results.
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    2. COYou seem to be checking whether the object is already in the set before you add it. I think this is probably an unnecessary complexity. Just add the service to the set, and let Cocoa and Core Data determine whether it's a) already there (an `NSMutableSet` doesn't allow the same object to be added twice) and b) whether there's a change that needs saving to the persistent store. Let the frameworks do the work for you where they can.
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    3. COI added that as a separate fix because I was getting duplicates. But that's a different story (I think). I know you can't have the same object but you can have two objects with the same data. And the save action was just an attempt to see if that was the problem. I wasn't saving them before.
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